Group 25 - Pressure Washer

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Contents

Introduction

This page documents the reverse engineering of a pressure washer water pump. This project was completed as an assignment by students in group 25 of the MAE 277 class at the University at Buffalo.

Members:
Alex Borsuk
Joe Keating
Scott Literman
Rich Seider
Kevin Walczyk

Contact: Kevin Walczyk

Executive Summary

This page documents each step of the reverse engineering of a pressure washer water pump. Our report describes in detail the processes of disassembly and reassembly of our product as well as the careful analysis of each component. This project was completed in a series of 5 gates, a system that is commonly used in industry today. Each gate required specific entry and exit criteria and had certain deliverables that needed to be provided to the instructors. The purpose of this project was to introduce mechanical and aerospace engineering students to real engineering problems and provide a means of applying what is learned in other engineering courses. In the fist gate, the request for proposal, our group outlined how we would approach the project. This included a project schedule, distribution of tasks, and an initial look at the product. Gate 2, the preliminary design review, required our group to develop a detailed plan to disassemble our product and then carefully document the actual disassembly process. In gate 3, the coordination review, our group was able to fully understand the internal workings of our product. In this gate we analyzed each internal component in great detail and then used solid modeling software to create renderings of these components. We determined how each component was manufactured, what purpose it served, and why it was engineered the way it was. In gate 4, the critical design review, our group reassembled our product and reflected back upon the project. We were able to develop several design revisions that we feel would have improved the product. In our 5th and final gate, the product delivery, our group finalized our report orally presented our results.

Gate 1: Request For Proposal

Information on the work proposal, management proposal, and schedule for this project will be available here[1]

Initial Product Assessment

Pw.jpg

The product being evaluated is a pressure washer. The pressure washer uses a high velocity stream of water to blast unwanted dirt, grime and other substances from almost any surface. It is designed to make washing exterior walls, walkways, driveways and other surface faster and easier than conventional cleaning methods.

  • This specific pressure washer is intended mainly for home use because of its smaller size. Larger pressure washers with bigger engines, stronger pumps, and the ability to heat water are used by professionals.

  • This product's general purpose is cleaning. This model features different shaped nozzle heads which can easily be switched, giving the optimal spray pattern for almost any cleaning job.

Our group will focus on the water pump component of the pressure washer. This device increases the pressure of the supply water before it reaches the nozzle. The pump for this model pressure washer is a reciprocating piston design, using either static or dynamic seals. The pistons reciprocate rapidly, drawing water in to the cylinder and expelling it higher pressure. The water then travels through the hose and out of the hand-held trigger nozzle. The small diameter of the nozzle creates a high-velocity, low-volume stream of water.

Considered as a system, the pressure washer relies on several energy conversions:

  • The mechanical shaft energy is transferred from the engine to the compressor’s pistons. These pistons then use their kinetic energy to pressurize the water forcing it out of the nozzle at a high velocity.

Our product is fully functional and is able to start and run.

  • The pressure washer runs very smoothly. It starts easily with a single "pull" and does not stall or hesitate while in use.

  • We are not experiencing any difficulties with the product this time. The product works as specified.

The water pump component is not a very complex machine. On a scale from one to ten, one being a person holding their finger over the end of a hose and a ten being a full sized fire engine, our compressor would be about a four.

Not including the fasteners which there are about twenty five of, the pump has about twenty parts. The main components of the pump include the manifold, pressure release, pressure valve, two bearings, an outer shell made of four sections, three inner pistons, a crankshaft, a water filter, and approximately seven or eight parts on the inside which are not visible before dissection.

  • Exterior components like the outer shell, water filter and fasteners must withstand corrosion, vibration, and abuse and are therefore simple and robust. Internal components include many moving parts needed to pressurize the water and are generally more complicated. There is an assembly on the inside of the shell which is similar to that of a valve train on an internal combustion engine, which is slightly more complex.

Our compressor is made of four main materials. They are brass, aluminum, steel and plastic.

  • The manifold is made brass. We know this because it has a distinct yellowish color and is non-magnetic. The outer shell of the compressor is made of aluminum. This is obvious because of its lighter weight, non-magnetism, and distinct white oxide layer. There are also plastic components present on the assembly, such as the pressure valve and oil plug.

  • We can assume that some of the inner parts of this compressor are made of steel. One of these parts is the compressor's crank shaft.

If we owned this product, we would be satisfied customers. The pressure washer is easy to move into position, has a high psi output, and functions as intended.

  • The pressure washer is very comfortable to use. It has wheels on the bottom making movement very easy to otherwise hard to get to locations. It also has a very long spray hose making it easier to reach difficult places. The handle to the sprayer itself has a hand grip making long jobs more comfortable.

  • Our product is very easy to use. It has a very reliable pull start motor that starts easily and runs well. Using the pressure washer once it is started is very simple. All you have to do is point the nozzle at your target area, pull the trigger and wait for the powerful blast of water.

The pressure washer requires very little maintenance. Engine and pump oil must be changed regularly and the air cleaner and water screen must be kept clean and free of debris.

Some alternatives to this model pressure washer include different size pressure washers and pressure washers that run on electricity instead of gasoline/diesel.

  • The main advantage of having an electric pressure washer is its lower retail price and ability to use indoors. The electric powered pressure washers are cheaper than their gasoline counterparts. However, larger, more powerful electric units may cost as much as their gasoline counterparts. Operating a gasoline/diesel pressure washer in a confined area is dangerous because of carbon monoxide poisoning from the exhaust. Electric pressure washers have no emissions, and thus, are safe to operate anywhere.

  • The main disadvantage of having an electric pressure washer is a less powerful water stream and limited range. The power cord limits the range of the washer whereas the gasoline models can go anywhere.

Gate 2: Preliminary Design Review

Causes for Corrective Action

Assessment of Group Progress

·         Our group is satisfied with the progress we have been making on our project. All deadlines have been met and we have achieved A grades on all assignments.

·         Work has been distributed evenly and fairly amongst the members. All group members have demonstrated responsibility as well as skill. Everyone in the group is contributing equally. Nobody feels left out and no one is overburdened with work.

·         Our work and management proposals and Gantt chart have proved to be essential in keeping our team on task. We are taking our deadlines seriously and have distributed work based on the strengths and weaknesses of our group members.

·         Group communication is excellent and meetings are being held regularly. Group meetings have been very productive and have had all group members in attendance.

·         Recent meetings have completed the following objectives:

  • Dissection of the product, distribution of work (10/21)

  • Collaborate on writing “Causes for Corrective Action” (10/24)

  • Collaborate on writing the step by step dissection analysis (10/26)

Unresolved challenges

As 10/27, the only unresolved challenge is obtaining CAD software. Our group has determined that we can complete the solid modeling component of the project more efficiently using software on our own machines.

Possible Solutions

·         Kevin will be contacting a high school professor to try to obtain a copy of Autodesk

·         Kevin will be writing to the company that produces Autodesk and Solid Works

·         Alex has antiquated solid modeling software installed on his computer

·         We will use the software in the campus computer labs if above solutions fail

Past Challenges and Solutions

Challenge:

A connecting rod in the pump sustained damage during re-assembly

Solution:

·         The instructor was notified of the damage to the product.

·         Our group reevaluated our procedure for doing hands-on work with the product. The group as a whole should have inspected the part more carefully and developed a more detailed plan for its installation. We could have prevented the damage to the connecting rod with a better assembly technique.

·         To resolve future problems of a similar nature, the team as whole will analyze the task at hand and nothing will be done until the entire team agrees to a specific plan of action.

Challenge:

There was a discrepancy among group members on how the pressure washer pump functioned

Solution:

·         Each group member shared his interpretation of the function of the component.

·         The group researched the component and gathered a wealth of information on the different types of water pumps used in pressure washers and how they functioned.

·         Each group member learned something new.

Challenge:

The presentation of the wiki page was not up to the group standards

Solution:

·         Alex, the wiki administrator, used internet resources to learn new techniques for creating better wiki pages

·         The group will produce more images and video to include in the wiki page

Product Dissection Plan

Our scale ranges from one to five. On our scale, a one is something that anyone can do with simple tools such as wrenches, and a five is something that takes multiple attempts and special tools and knowledge.

Step Number

Process

Tool

Level of Difficulty

1

Remove the top plate of the aluminum housing covering bearing by unscrewing 4x (½”) Allen head bolts.

Allen Wrench (3/16”)

1

2

Remove brass manifold from aluminum casing by unscrewing 8x (½”) Allen head bolts. A flat-head screwdriver can be used to help pry the brass manifold from the aluminum casing.

Allen Wrench (3/16”)

Flat-head screwdriver

2

3

Remove aluminum side cover from aluminum housing by unscrewing 6x ( ½”) Allen head bolts

Allen Wrench (3/16”)

1

4

Remove section that connects the engine to the compressor by removing 4x (½”) Allen head bolts. Do to the space constraints, an additional lever arm on the wrench is recommended.

Allen Wrench (3/16”)

Lever Arm (pipe or tube)

3

5

Remove aluminum snap ring from bearing revealed in step 1. Use two flat-head screwdrivers to push the snap ring ends in opposite directions. This will cause it to slide off. The use of snap wring pliers over screwdrivers is not required but is highly recommended.

Snap wring pliers

(or)

2x Flat-head screwdriver

2 w/ pliers

4 without

6

Remove red oil filler plug from side the side of the aluminum casing.

By hand

1

7

Using a bearing/hydraulic press, press out the central steel shaft very carefully. The side revealed in step (1) should be facing up and pressed on to push it into the aluminum housing.  As you press the shaft out, use a flat-head screwdriver to move the three aluminum rings off the cams. While doing so slowly work the shaft out the other end. This part is very crucial or you will break the rings.  Once the shaft is to a level which the press cannot directly push on, it is necessary to place small spacers on the shaft that are smaller than the bearing hole. As you press on the spacers, you press only on the shaft and not the bearing.

Hydraulic/bearing press

Flat-head screwdriver

Small spacers

5

8

Remove the nuts from the three pistons using a ½” wrench. Remove the 2 copper washers and ceramic spacer from each piston.

Open-end wrench (1/2”)

1

9

Push the three pistons into the aluminum housing and then remove.

By hand

1

10

Remove the other remaining bearing by using the hydraulic/bearing press to press it out.

Hydraulic/bearing press

1

 

 

Product Dissection Images

G2-1.jpg
G2-2.jpg
G2-3.jpg
G2-4.jpg

Gate 3: Coordination Review

At this stage of our project, our group has finished analyzing the product and its assorted components. We have not encountered any problems since our last cause for corrective action was submitted.

Component Summary
The pump assembly of the pressure washer consists of several components and sub-assemblies:

The manifold assembly:

  • Brass manifold

Manifold1.jpg

  • Manifold screws

Manscrews.jpg

  • Water screen

Piston assembly

  • Ceramic piston

Ceramic.JPG

  • Connecting rod

Connecting.JPG

  • Piston hardware

Hardware.JPG

Shaft assembly

  • Central shaft

Shaft1.jpg

  • Roller bearing
  • Sealed ball bearing
  • Snap ring

Bearings.jpg

Housing assembly

  • Housing

Housing1.jpg
Housing2.jpg

  • Housing cover

Coverplate.jpg

  • Plastic plug

Plug.jpg

  • Housing spacer/shaft concealer

Spacer1.jpg

  • Housing cap

Cap1.jpg

  • Spacer Screws

Capscrews.jpg


Detailed Component Summary:

Brass Manifold
Why were different materials selected for different components?

  • Brass was used for the manifold for multiple reasons. First, brass has a high fluidity when molten so it is easy to cast. This makes getting a high level of detail easier. Second, brass does not corrode easily. This increases the life expectancy of the pressure washer. There are also ceramic plates in the slots where the pistons go in and out of. These plates are ceramic because ceramic rubbing on ceramic does not create as much friction and heat has a metal rubbing on a metal.

What forces are applied to the components?

  • There are forces applied on the manifold from both the piston moving in and out as well as the water passing through it at a high velocity
  • A reasonable estimate for the force exerted on the manifold by the pistons is 20 pounds. The water enters the manifold at about 60 psi and leaves at over 2000 psi. This pressure is constantly being forced on the inside of the manifold. The manifold must be able to withstand these high pressures.

Does the material choice affect the manufacturing process?

  • Yes. Designers could use the die casting method because brass flows easily as a liquid into many tight spaces. They were able to get a fine surface finish as well as a good detail. If a different metal was chosen with a lower fluidity, other methods such as investment casting would have been needed.

Does the shape affect the manufacturing process?

  • Yes. Because this manifold has many complex cavities or compartments, die casting is a good choice. Also, the sides of the pump needed to be thick to withstand the high forces applied during use. If the walls were thinner, a different casting process could have been used.

Why was each manufacturing process chosen for that component?

  • Designers used die casting for multiple reasons. First, Brass has a high fluidity so it would flow easily into the little crevices of the mold. Second, the manifold is a medium sized part (less than 24’’) so it is not too big to die cast. Third, many of these parts can be made cheaply because die casting is very economical for large runs. Also, each manifold made is dimensionally consistent with the one made before it as well as the one made after. This is a production part. Since a large number of theses identical manifolds must be manufactured, die casting is more economical and faster than machining.

Do any components have a particular shape? Why?

  • Yes. The inside of the manifold is full of ducts, all having rounded corners and edges. This is because water is flowing through the pipes at a high rate of speed. The rounded corners inside the manifold makes the water flow through it was less drag, increasing its output psi.

Is the component functional, cosmetic, or a combination of the two?

  • The manifold is a combination of both functional and cosmetic. It has a fine surface finish due to the die casting method. Also the brass color has a good appeal with this surface finish. The brass finish shows that the manufacturer did not use an inferior material. This part is also necessary for the function of the pump. It takes water in at about 60 psi and within a fraction of a second, expels the same water at over 2000 psi. It does this constantly at a very high rate of speed. It is more important that the component is functional, but there is always a want for some sort of aesthetic appeal.

How complex is the component?

  • The component is very complex. Compared to the entire assembly this component would be somewhere around an 8, the screw being a one, the housing being about a five and the cam shaft and bearings being an eight or nine on this scale. It has a system of pipes which transfer water from the inlet to the outlet with many stages in between. The first stop is passing the water through the filter. It then spills the water into three small compartment s which are almost immediately pressurized by the pistons moving in and out of them. The now highly pressurized water is expelled through the outlet and can be used to clean many surfaces. These multiple steps occur in a fraction of a second. It has a very complex design.

Mesh Water Filter

The function of this component is to filter the water coming into the pump. This makes sure that no sticks, leaves, or other solids that may be present in a garden hose do not clog up the pump, causing a system failure. The edge of the filter is made from a stiff rubber probably made using injection molding. There is evidence of mold lines as well as risers. The filter itself is made from an aluminum mesh. It is made by weaving an aluminum wire in a plain weave pattern.

Why were different materials selected for different components?

  • For the mesh water filter there were two materials used, rubber and aluminum. The rubber edging was used because it is very flexible and has a high shape memory. It creates a great seal between the hose attachment and the manifold. The aluminum was used to make the mesh because aluminum does not corrode very easily.

What forces are applied to the components?

  • When the pressure washer is in use, there is a constant force from the hose water pressing through the mesh. The mesh needs to be strong enough not to tear under this pressure. The Rubber edging must be resilient enough not to lose its seal when this water pressure is applied.
  • The average home’s water pressure is about 60 psi. All of this pressure is being applied to the filter because all water that goes into the pump must go through this filter.

Does the material choice affect the manufacturing process?

  • Yes. Because the edging is rubber, machining would be impractical. Most plastic and rubber components are made using the injection molding process because they have a very low per part cost.

Does the shape affect the manufacturing process?

  • Yes. If you are making a simple object such as the circular edging around the mesh, it is very cost effective to use the injection molding. It more economical to make each individual part and make each part exactly the same shape. If it was a more complex component, a different process would need to be used.

Why was each manufacturing process chosen for that component?

  • The rubber edging was made by injection molding because it is the only economical way to produce it. Had it been machined, there would be a very high amount of waste. Either form of casting would be very expensive and wouldn’t work very well. Weaving was used on the aluminum mesh because it is the quickest and most cost effective method. There is very little waste material from weaving and large areas of mesh can be made relatively quickly.

Do any components have a particular shape? Why?

  • The rubber O-ring edging is circular because it needs to make a waterproof seal with the edge of the manifold input valve. The aluminum mesh has a plain weaving pattern because it is the simplest weaving pattern allowing for water to pass through quickly yet still allowing for the filtering process to occur.

Is the component functional, cosmetic, or a combination of the two?

  • This component is strictly functional. When in use, the filter cannot be seen because it is completely covered by the hose and manifold. Its job is to filter the water coming into the pump and that is all it does.

How complex is the component?

  • The component is relatively simple. The filter is simply a coarse metal screen with no moving parts. The edging is a circular piece of rubber that creates seal between the mesh and the manifold. Compared to the entire assembly this component would be somewhere around a 3, the screw being a one, the housing being about a five and the cam shaft and bearings being an eight or nine on this scale. It is a very important component in the pump, but it is still relatively simple.

8 (½”) Allen Screws

The function of the Allen screw in this part of the pump is to hold the brass manifold flush with the outer casing without moving. The screws are made of a brass compound. They are manufactured with a combination of cold rolling, forging and machining. We know this because the head of the screw is forged to give its required tool shape. It is cold rolled to give the screws their threaded shafts. It is machined in the beginning when the blank screws are sliced from the giant metal coil of wire.

Why were different materials selected for different components?

  • For these screws the designers used a brass compound. They did this because brass does not rust easily. Materials which build rust would not practical on an object which on always getting wet. Corrosion makes removal of the screws difficult and could lead to failure.

What forces are applied to the components?

  • There are forces applied to the screws from the constant movement of the pistons. They must hold the brass manifold flush with the outer casing without slipping creating a tight seal. They must also allow the pistons to move.
  • The motor provides upwards of ten horsepower to the cam shaft. Almost all of this power is transferred to the pistons which apply this force on the brass manifold. The combination of 8 screws must support this forced which is constantly being applied to the brass manifold.

Does the material choice affect the manufacturing process?

  • Brass is a softer metal allowing designers to use a thread rolling method to make the screws. Beginning as a long coiled wire, the wire is cut the desired length of the screw. Next, one end of each blank is pressed and compressed to form its head. Then the shape of the tool (allen in this case) is forged into the head. Finally, the blank is cold-rolled along a harder metal form with a threaded shape giving each screw a threaded shaft. This cold rolling gives the object a high amount of strength but it sacrifices ductility.

Does the shape affect the manufacturing process?

  • Because these screws are for the most part cylindrical, they can begin as a long coiled wire and be literally sliced into their desired lengths. Had they been another shape, a different manufacturing method would be needed.

Why was each manufacturing process chosen for that component?

  • This manufacturing process was chosen because it is the most cost effective method. It has a very low cost per screw.

Do any components have a particular shape? Why?

  • These screws have a straight cylindrical shape because that is the best shape for a screw. The threads on the end of the screw allow it to grip to its desired surface without slipping. The head is wider than the shaft of the screw because it must be able to stop the screw from spinning once it is at its desired depth into the hole.

Is the component functional, cosmetic, or a combination of the two?

  • The screw would definitely be considered more or a functional object than a cosmetic one. Its shaft is hidden and only the head is visible. The most important factor in making this screw is making it strong and corrosion resistant. Corrosion resistance also has affects aesthetics, as rust is unsightly.

How complex is the component?

  • The object is itself extremely simple. It has no moving parts. In fact, it is made so that it does not move. Once it is installed, only routine tightening is needed to keep these screws performing as needed. This component forms that base of our scale, as it is the simplest part of the pump assembly. The screws have a complexity of 1 on a scale where the housing is about a five and the cam shaft and bearings are about an eight or nine.

The piston

The function of this component is to pressurize and expel water on the pump’s compression stroke and draw water into the cylinder on the intake stroke. The piston is made from a ceramic material.

Why were different materials chosen for different parts?

  • Ceramic was chosen as the material for the piston because ceramic has low frictional properties compared to most metals and is able to withstand high temperatures.

What forces are applied to the components?

  • With each rotation of the shaft, the piston is pushed upwards by the force of the connecting rod attached to the crankshaft. The piston must push against the water in the cylinder, which has a resistance to flow. I estimate this force as 20 pounds for each piston.
  • The piston is subject to frictional forces against the ceramic lining of the cylinder wall. It is difficult to estimate what this force will be, because the piston is lubricated by the water in the pump. During disassembly, we noticed very little static friction.

Does the material choice affect the manufacturing process?

  • It is difficult to manufacture ceramics due to the nature of the material. Although ceramics can be machined, their hardness usually prohibits this. This component was most likely formed in a mold at high temperature.

Does the shape affect the manufacturing process?

  • The outside diameter of this piece demands very high precision. Although a lathe would be an ideal machine for this, the hardness of ceramic prevented its use. The piston has a hole along its axis that makes the component a tube. This would normally be drilled. However, since ceramic is difficult to machine, this was most likely incorporated into the mold.

Why was each manufacturing process chosen for that component?

  • I believe that the mold that this component was fired in was similar to those used in investment casting. There was no seam present and the surface finish was impeccable. If a 2-piece mold was used there would be a seam present. This would be very difficult to machine off to achieve the desired surface finish.

Do any components have a particular shape? Why?

  • The piston is shaped to slide into the cylinder with a very tight tolerance. The piston has a hole along its central axis that allows it to be attached to the connecting rod.

Is the component functional, cosmetic or a combination of the two?

  • The component is completely functional. It has been made to serve its purpose, not to be aesthetically pleasing. The component is internal and is not visible to the user. This component is key to the function of the pressure washer.

Why do you think the manufacturing process was chosen for a given component?

  • The manufacturer of the piston had very few choices of processes used to make the ceramic component. The manufacturer chose the most economical method of creating the component. The piston was most likely produced by a company that specializes in ceramics and was not made in-house.

How complex is the component?

  • The ceramic piston would rate at about a 2 on the complexity scale with a screw or snap ring being a one and the cam shaft and bearings being an eight or nine. Although it is a very simple part, the material is somewhat exotic and it required a unique manufacturing process.

The Connecting Rod

The connecting rod is a small, inseparable assembly that transfers the rotational motion of the crankshaft into linear motion of the pistons. The connecting rod consists of a steel rod that is threaded on one end to accept a piston and an aluminum hoop that rides on the crankshaft. These two pieces are connected with a pin that was pressed in with a very large press and cannot be removed.

Why were different materials chosen for different parts?

  • The upper rod was made from steel because it is subject to high loads and has threads at the top. The lower hoop is made from aluminum because when well lubricated, steel and aluminum have lower friction than steel on steel.

What forces are applied to the components, what are their magnitude?

  • The upper rod is subject to the same axial force as the piston, which we estimated at 20 pounds. The rotation of the lower hoop creates additional forces and moments, which vary throughout the cycle of the pump. The hoop experiences a frictional force when rotating on the shaft. When lubricated, this is very low, perhaps about 1 pound.

Does the material choice affect the manufacturing process?

  • The steel rod is machined and the aluminum hoop is cast. The material choice does not affect the choice of manufacturing process as much as shape does in this instance.

Does the shape affect the manufacturing process?

  • Shape is the biggest factor in manufacturing process for this component. The upper rod and lower hoop have distinct shapes that call for different manufacturing processes. The rod is mostly symmetrical, but has a flat section where it connects to the aluminum hoop. The aluminum hoop has a unique shape and a precise inside diameter, as well as a hole. This cannot be achieved effectively using a single manufacturing process.

Why was each manufacturing process chosen for that component?

  • The steel rod was first turned on a lathe to achieve the symmetrical features and threads. Then the flat section where it meets the lower piece was cut on a milling machine and the hole was drilled. The aluminum piece was die cast and the inner diameter was machined. The inner diameter requires a very high precision surface to maintain a thin film of oil between it and the crankshaft.

Do any components have a particular shape? Why?

  • The lower aluminum hoop is shaped to match the surface of the crankshaft with very tight tolerance. The rod is designed to not be obtrusive and not make contact with other components throughout the pump stroke. All parts are symmetrical to ensure the pump is balanced.

Is the component functional, cosmetic or a combination of the two?

  • The component is completely functional. It has been made to serve its purpose, not to be aesthetically pleasing. The component is internal and is not visible to the user. This component is key to the function of the pressure washer.

Why do you think the manufacturing process was chosen for a given component.

  • Turning was used to make the initial shape of the rod because it is the most efficient method of produce a symmetrical piece. The two holes that are present in this component were most likely drilled because the rod was produced from a billet and the aluminum piece was cast. Although holes can be cast, in this case, an extremely tight tolerance is needed for the press fit pin. Thus, the hole was drilled.

How complex is the component.

  • The connecting rod would rate about a 6 on the complexity scale with a screw or snap ring being a one and the cam shaft and bearings being an eight or nine. Although this is a moving part, it is very simple. There is only one point of motion, which occurs in one plane. The steel rod and aluminum hoop have some features that would require several machining processes.

Piston Hardware

The piston hardware consists of a retaining nut, a small brass washer, and a large brass washer. The purpose of the retaining nut and small washers is to keep the ceramic piston attached to the connecting rod. The washers prevent the ceramic piston from binding when tightened.

Why were different materials chosen for different parts?

  • The nut is made out of stainless steel for strength and corrosion resistance. Although brass and aluminum also resist corrosion, stainless steel is far stronger. The washers are made from brass because they

What forces are applied to the components, what are their magnitudes?

  • When the nut is tightened, the brass washers and the nut itself experience static friction and normal forces. The normal forces vary with the stroke of the pump but a reasonable estimate of the maximum force would be 20 pounds. The only force that works to loosen the nut is vibration.

Does the material choice affect the manufacturing process?

  • Material composition impacts the manufacturing process. Complexity aside, it is more difficult to manufacture the stainless nut than the brass washers because stainless steel is much harder than brass.

Does the shape affect the manufacturing process?

  • The shape definitely affects the manufacturing process. The brass washers have a very simple shape that can be easily punched out of sheet metal. The shape of the nut requires several machining processes be combined in its manufacture.

Why was each manufacturing process chosen for that component?

  • The brass washers are most likely punched out of sheet metal. Although this creates significant waste, the process is so simple and economical that it is negated. The nut requires high strength and must be made very quickly, and in large quantities. Thus, a combination of forging and tapping is used to make the nut.

Do any components have a particular shape? Why?

  • The piston must stay in place during use while being subject to shock vibration. The most effective means of keeping it secured having it screw into place. The threads on the nut accomplish this. The nut has a hex shape that allows it to be tightened easily. The washers are flat so that they do not bind against the ceramic piston.

Is the component functional, cosmetic or a combination of the two?

  • The component only serves a functional purpose. The component is hidden from the user at all times.

Why do you think the manufacturing process was chosen for a given component.

  • These components were most likely not made in house. The nuts and washer were made in very large production runs with low profit margins. Forging and tapping the nuts with automated machinery much faster and more economical than combining milling and turning for example. The washers could be machined or cast, but a single die can punch out hundreds of washers in a matter of seconds.

How complex is the component.

  • Compared to the entire assembly, the piston hardware would rate as a 1, among the most simple parts. A screw or snap ring would also be a one, the housing would be about a five and the cam shaft and bearings would be about an eight or nine on this scale. It is very important that this hardware does not become loose. However, threadlocking compound can make this easier to accomplish.

The Central Shaft

This component is the central shaft of the pump. It is used in our product once. It converts the input torque from the motor into linear motion of the pistons to pressurize the water. It accomplishes this task by having 3 cylindrical sections offset from the center of the shaft. These eccentric sections travel in orbits around the rotational axis of the shaft and move the connecting rods up and down. The side that connects to the engine has a keyway, which is used to connect the 2 shafts. It also has a cylindrical section cut to fit in a roller bearing. On the end opposite the engine, there is a smaller cylindrical section that is made to press fit into a bearing and a groove cut to fit a snap ring.

Why were different materials chosen for different parts?

  • This piece is made of steel because it is required to have high strength. The surface finish must be flawless where it interfaces with the connecting rods and bearings.

What forces are applied to the components?

  • The piece takes an input torque estimated at around 10 ft*lb as well the reaction force imparted by each piston stroke. I estimate this at approximately 20 pounds. A slight kinetic frictional force is developed at the bearings and connecting rods. This is most likely only a few pounds. Most friction is caused by the pistons.

Does the material choice affect the manufacturing process?

  • The choice of using steel for the part affects the manufacturing process. Steel takes longer to machine than softer metals, such as aluminum. Also steel can be ground, whereas aluminum is not well suited for that process.

Does the shape affect the manufacturing process?

  • The shape has a large effect on the manufacturing process. Features that are symmetrical about the axis of rotation can be created on a conventional lathe. However the 5 eccentric sections cannot be. A special machine called a crankshaft lathe exists that can cut these sections. The part cannot be made on a milling machine because of the high tolerance circular sections. Casting would not provide a surface finish that is precise enough for the bearings and connecting rods. Casting is most likely used to create the rough shape of the shaft. The keyway that allows the shaft to connect to the engine could be cut on a mill.

Is the component functional, cosmetic, or a combination of the two?

  • Although it may look cool, aesthetics was not a design consideration, as this is an internal part. This part is key to the function of the pressure washer. There are obvious mold lines between the machined sections on the shaft. These sections could have been machined or polished for aesthetical purposes, but were not.

How complex is the component?

  • This component has a medium amount of complexity, around a 5 on a scale of 1 to 10. It has less complexity then a crankshaft in a car engine but more then a part completely symmetrical about the central axis. It would take multiple machining processes because of the 5 center sections and the keyway which is why it has a medium amount of complexity.

The bearing on the left is a roller bearing used to hold the shaft with minimal friction where it meets the engine. This bearing is lubricated with the oil in the housing. The bearing on the right is a sealed ball bearing that holds the opposite end of the shaft with minimal friction. This bearing is packed with grease. The snap ring fits on the end of the shaft and holds it in place.

Roller Bearing

Why were different materials chosen for different parts?

  • The bearings and races are made from a high grade of hardened steel. The hardened steel has low friction properties, is very durable, and is able to withstand high loads and temperatures.

What forces are applied to the components?

  • The bearings receive no axial load but must support a radial load equal to the loads on the shaft. The loads on the bearings fluctuate with the cycles of the pump. A good estimate of the maximum load on each bearing would be 10 pounds.

Does the material choice affect the manufacturing process?

  • The hard steel used in the rollers and races makes machining difficult. Casting does not produce hard steel. The races are most likely made on a lathe out of a hard grade of steel and polished. The rollers are forged, the flashing is ground off, and they are then polished.

Does the shape affect the manufacturing process?

  • The shape and required tolerances of the balls and rollers make milling and turning impossible. The races must are also round and must be precise, so milling is not practical.

Is the component functional, cosmetic, or a combination of the two? The component is for functional purposes and its shapes are very important. These are internal components that are critical to the function of the pump. The surfaces are polished for tight tolerance and low friction, not aesthetics.

How complex is the component?

  • This component is moderately complex and emphasis is placed on tight tolerances. On a scale of 1 to 10 I would rate it a 5, a 1 being a simple shaft and a 10 being an automobile engine. While the snap ring is simple, the bearings are quite intricate. The roller bearing consists of many parts, including the outer race, the retainer, and the individual rollers.

Sealed Bearing

Why were different materials chosen for different parts?

  • This piece is made of steel as well as a plastic cover because aluminum is too soft. Aluminum would also wear too quickly causing increased friction and requiring the component to be replaced.
  • The seal on the sealed bearing is made from plastic. Plastic is flexible and can form a lip seal around the inner race.

What forces are applied to the components?

  • This piece receives little axial loads but must support the same radial loads as the roller bearing on the other side of the shaft, estimated at a couple hundred psi. The force is high because the component is a press fit in the housing.

Does the material choice affect the manufacturing process?

  • The hard steel used in the rollers and races makes machining difficult. Casting does not produce hard steel. The races are most likely made on a lathe out of a hard grade of steel and polished. The balls are forged, the flashing is ground off, and they are then polished.

The seals are made from very soft plastic and must be injection molded.

Does the shape affect the manufacturing process?

  • The shape and required tolerances of the balls and rollers make milling and turning impossible. The races must are also round and must be precise, so milling is not practical. The seal is made from a soft plastic, so the possibility of almost all types of machining is eliminated.

Is the component functional, cosmetic, or a combination of the two?

  • The component is for functional purposes and its shapes are very important. This is an internal component that is critical to the function of the pump. The surfaces are polished for tight tolerance and low friction, not aesthetics.

How complex is the component?

  • This component is moderately complex and emphasis is placed on tight tolerances. On a scale of 1 to 10 I would rate it a 5, a 1 being a simple shaft and a 10 being an automobile engine. While the snap ring is simple, the bearings are quite intricate. Under the seal there are many parts, including the outer race, inner race, the retainer cage, and the individual balls.

Snap Ring
The snap ring is used to make sure that the shaft cannot come free of the assembly.

Why were different materials chosen for different parts?

  • The snap ring is made from mild steel to give it spring properties.

What forces are applied to the components?

  • This piece only supports loads if the shaft manages to slip in the bearing which is unlikely because it is a press fit. However if it did slip it would only take the horizontal forces on the shaft which should be virtually 0. Under normal conditions, the load on this part can be considered negligible.

Does the material choice affect the manufacturing process?

  • The component’s shape and thickness are a bigger factor than material for this component.

Does the shape affect the manufacturing process?

  • Since the component is very thin and only has features in a flat plane, it can easily be punched out of sheet metal. This process is both fast and economical, although some waste is expected.

Is the component functional, cosmetic, or a combination of the two?

  • The component is for functional purposes and its shape is important. It needs to be thin enough to fit in the groove and the two holes in it allow it to be removed with the proper tool. The spring properties it possesses depend on where the metal is distributed on the part.

How complex is the component?

  • This component is not very complex although some emphasis must be placed on tight tolerances. On a scale of 1 to 10 I would rate it a 2, a 1 being a simple shaft and a 10 being an automobile engine. Although by design, it is very simple, if the tolerances are off, it will not function properly.

The Housing

The function of this component is to house or contain the vital internal components while keeping them well lubricated in a reservoir of oil and distributing the heat caused by friction into the surrounding environment. The housing is made from cast aluminum. A die casting process was used to manufacture the housing. There is evidence of residual risers, there aren’t any sharp corners and the external cooling fins have a tapered shape, all of which indicate die casting was used. After the initial casting there was limited machining involved in creating this part. All the surfaces that contacted other metal were finished to allow a good seal between surfaces and avoid oil leakage. Also there are threads that have been tapped into the part, these need to be precise and smooth, they cannot be formed during the cast. No model or serial numbers were present.

Why were different materials chosen for different parts?

  • Different materials are chosen obviously because different materials are suited to perform different tasks. Some materials are better suited and have more of an advantage for certain jobs.

What forces are applied to the components?

  • The housing is subjected to static forces that are in equilibrium. At each point of contact between the housing and its two covers there are multiple screws that apply distributed loads on each surface. I estimate the pressure exerted on the plates by the screws is less than one hundred pounds. Also there are two bearings that are pressed into the housing, so around each bearing there are stresses and forces exerted on the housing from the compression of the bearing case. Tension is exerted by the stress of the housing trying to squeeze the bearing from the outer circular surface. I estimate these forces to be well upwards of one hundred pounds because it took two large men with the aid of a manual bearing press and along lever to effectively move the bearings out of the system.
  • The assembly experiences thermal effects created by friction. The housing is designed to conduct heat and dissipate it through the cooling fins. Aluminum has high thermal conductivity so it can dump this heat into the surrounding environment. I estimate this temperature doesn’t normally exceed 100 degrees Celsius.

Does the material choice affect the manufacturing process?

  • Material composition most certainly impacts the manufacturing process. In this case the aluminum is a common casted material. It can be melted and forced into a mold. The aluminum has a relatively low melting temperature compared to other metals. When liquefied, it flows fairly easily into the spaces and cavities of the mold, which is ideal for this application.

Does the shape affect the manufacturing process?

  • The shape definitely affects the manufacturing process. Some shapes are impossible to mold if they are too complex with multiple cavities and compartments within the part. Also, it wouldn’t make sense to mold something simple like a rod or a component that must bear extreme forces. In fact, cast objects can be very brittle. If the casting has certain spots that are shaped thin and must endure large forces, an alternative method would be more appealing. An example would be a socket for a wrench. The shape allows it to be cold forged from a single plug of metal. Cold forging is when a room temperature piece of stock is pressed under immense pressure to the desired shape. The result is a very strong, durable piece of metal which would be desirable in a socket that must withstand large forces to tighten and loosen nuts and bolts.


Why was each manufacturing process chosen for that component?

  • The housing was die cast because it was determined to be the most effective, efficient and economical way to produce the part. With number of cooling fins, orifices and main cavity it would take a serious amount of time to machine, and there would be significant waste. The part’s shape is too complex to be forged or stamped. This is a full production model, many duplicates of this part must be made. Once a mold is created it can be reused, reducing production cost. Aluminum flows easily as a liquid at a relatively low temperature and can be forced into a mold easily.

Do any components have a particular shape? Why?

  • Yes, components often are shaped to fit the desired need and purpose. Often the required performance of the part dictates the shape. For example the housing has many ridges or fins which may appear to look odd. In reality this wasn’t done to get an interesting aesthetic appeal this was done to increase the surface area for heat transfer. The fins can dissipate more heat to the ambient air than a smooth surface would. The housing is a hollow block because it must contain components and a lubricant inside. In addition, components may have to fit within a specified area greatly constraining the size and shape of the part.

Is the component functional, cosmetic or a combination of the two?

  • The component is predominantly functional. It has been made to serve its purpose not to be aesthetically pleasing. It houses the components and efficiently transfers heat from friction and combustion to the external thermal sink. However, there is always a little cosmetic influence to a designing a part. The part looks clean and well crafted, not something that was just slapped together with a complete disregard to the appearance.

Why do you think the manufacturing process was chosen for a given component.

  • The housing was die cast because it is the most effective efficient and economical way to produce the part. Once the mold was created it can be reused. Aluminum flows easily as a liquid so it can be forced into a mold easily. With number of cooling fins, orifices, and main cavity it would take a serious amount of time to machine not to mention the amount of waste material. The part’s shape is too complex to be forged or stamped. This is a full production model so there are a lot of duplicates. The more the mold is used the initial overhead expenditures become more and more worthwhile.

How complex is the component.

  • Compared to the entire assembly, the housing would be somewhere in the middle on the scale (about a four or five), with a screw or snap ring being a one and the cam shaft and bearings being an eight or nine. It has specific needs that need to be met. The dimensions and placement of the orifices are critical. The holes must align so it connects to the engine output while the mounting holes simultaneously align allowing it to be fastened to the engine. The addition of the cooling fins increase it’s rank of the scale of complexity slightly compared to a simple block. The most important aspect of this part is that it must properly fit together with the rest of the components of the assembly.

The Shaft and bearing cover plate

The bearing cover plate attaches to the housing to seal and protect the bearing and the rotating end of the shaft. There are four short hex-head screws which apply force at each of the corners of the cover and thread into the housing. The plate has a small thin rubber gasket, which provides a seal between the two machined metal surfaces protecting the bearing and rotating shaft from damage and foreign material. The cover is necessary because the product cannot be made without a hole on the side of the housing to put the shaft through. After it is fully assembled the exposed parts need protection so this cover is placed over the opening providing a tightly sealed compartment. This is made of the same material as the housing, which is cast aluminum. The manufacturing process is die casting along with machining of the contact surfaces. There is only one of these and there is not an available part number.

Why were different materials chosen for different parts?

  • Different materials are chosen obviously because different materials are suited to perform different tasks. Some materials are better suited and have more of an advantage for certain jobs. This component was made of the same material as the housing because of aluminum’s thermal properties and ease of manufacturing.

What forces are applied to the components, what are their magnitude?

  • The cover is subjected to static forces that are in equilibrium. At the point of contact between the housing four screws apply point loads on the contact surface. I estimate the pressure exerted on the plate by the screws is less than one hundred pounds. This part along with the rest of the assembly experience thermal forces as well. The heat is conducted into the plate and cooling fins. Aluminum has high thermal conductivity so it can dump this heat into the surrounding environment which is a cold sink. I estimate this temperature doesn’t normally exceed 100 degrees Celsius or so it does not damage the rubber o-ring.

Does the material choice affect the manufacturing process?

  • Material composition impacts the manufacturing process. Aluminum is a commonly cast material. It can be melted and forced into a mold. The aluminum has a relatively low melting temperature compared to other metals. When liquefied it flows fairly easily into the spaces and cavities of the mold.

Does the shape affect the manufacturing process?

  • The shape most certainly affects the manufacturing process. Some shapes are impossible to mold if they are too complex with multiple cavities and compartments within the part. Also it wouldn’t make sense to mold something simple like a rod or a component that must bear extreme forces. In fact casted objects tend to be very brittle. If the shape has certain spots that are shaped thin and must endure tremendous forces an alternative method would be more appealing. For example a craftsmen socket. The shape allows it to be cold forged from a single plug of metal. Cold forging is when a room temperature piece of stock is pressed under immense pressure to the desired shape. The result is a very strong durable piece of metal which would be desirable in a socket which must withstand large forces to tighten and loosen nuts and bolts.

Why was each manufacturing process chosen for that component?

  • The cover was die casted because it is the most effective efficient and economical way to produce the part. Once the mold was created it can be reused. Aluminum flows easily as a liquid so it can be forced into a mold easily. With cooling fins, it would take time to machine not to mention the amount of waste material. The part’s shape is too complex to be forged or stamped. This is a full production model so there are a lot of duplicates. The more the mold is used the initial overhead expenditures become more and more worthwhile.

Do any components have a particular shape? Why?

  • Yes, components often are shaped to fit the desired need and purpose. Often the required performance of the part dictates the shape. For example the cover has many ridges or fins which may appear to look odd. In reality this wasn’t done to get an interesting aesthetic appeal to match the housing this was done to increase the surface area for heat exchange. The fins more efficiently conduct head to the ambient environment than a smooth blocked surface. The plate fits tightly onto the housing protecting the bearing and end of the shaft. In addition components may have to fit within a specified area greatly constraining the size and shape of the part.

Is the component functional, cosmetic or a combination of the two?

  • The component is predominantly functional. It has been made to serve its purpose not to be aesthetically pleasing. It fits tightly to the housing and protects the ball bearing and end of the shaft and efficiently exchanges the internal heating from friction to the external thermal sink. There is always a little cosmetic influence to a designing a part though, the part should appeal clean and well crafted not something that was just slapped together with a complete disregard to the appearance.

Why do you think the manufacturing process was chosen for a given component.

  • The cover was die casted because it is the most effective, efficient, and economical way to produce the part. Once the mold was created it can be reused. Aluminum flows easily as a liquid so it can be forced into a mold easily. The cooling fins would take a great amount of time to fully machine, not to mention the amount of waste material that would be produced. The part’s shape is too complex to be forged or stamped. Many duplicates of this part must be made. The more the mold is used the initial overhead expenditures decrease.

How complex is the component?

  • Compared to the entire assembly the cover would be somewhere towards the bottom of the scale (about a two), the screw being a one, the housing being about a five and the cam shaft and bearings being an eight or nine on this scale. It has specific needs that need to be met. The dimensions and placement of the holes are critical to match the placement of those on the housing as well as fitting tightly into the specified location. The addition of the cooling fins only slightly increases its rank of the scale of complexity


Plastic threaded oil plug


This component is designed to allow the oil containing housing to be filled or drained. The plug which only appears once must match the threads on the housing and seal tightly; not allowing oil to leak from its location. The hard plastic plug was injected molded because you can easily see the mold lines and residual risers. The threads were created with a die which cuts the threads into the material. The plastic plug was designed so that it can easily be placed or removed by hand or with an open-end wrench. A part number is not present.

Why were different materials chosen for different parts?

  • Different materials are chosen obviously because different materials are suited to perform different tasks. The difficulty and cost of manufacturing often depends on the choice of materials.

What forces are applied to the components, what are their magnitudes?

  • Torque must be applied to loosen and tighten the plug once it is sealed. These forces are relatively small, and can be achieved by the human hand. I estimate them to be less than 10 ft lb.

Does the material choice affect the manufacturing process?

  • Material composition impacts the manufacturing process. Injection molded plastic is used for this part. The plastic is melted and forced into a mold. The plastic has a relatively low melting temperature compared to other materials. When liquefied it flows fairly easily into the spaces and cavities of the mold, which is ideal.

Does the shape affect the manufacturing process?

  • The shape definitely affects the manufacturing process. Some shapes are impossible to mold if they are too complex with multiple cavities and compartments within the part. In the case of the plastic oil plug, injection molding was the best manufacturing process. Injection molding can produce a wide variety of shapes and is relatively inexpensive.

Why was each manufacturing process chosen for that component?

  • The plastic oil plug was injection molded because it is the most effective efficient and economical way to produce the part. Once the mold was created it can be reused. Plastic flows easily as a liquid so it can be forced into a mold easily. This is a full production model so there are a lot of duplicates. Injection molding can produce a wide array of shapes.

Do any components have a particular shape? Why?

  • Yes, components often are shaped to fit the desired need and purpose. Often the required performance of the part dictates the shape. This part must stay in place during use while being subject to shock vibration. The most effective means of keeping it secured having it screw into place. Thus, the component has threads.

Is the component functional, cosmetic or a combination of the two?

  • The component is predominantly functional. It has been made to serve its purpose not to be aesthetically pleasing. It fits tightly to the housing and prevents oil leakage at this location. The top of the plug is red, which was not necessary, but makes it easier to see against the black casting.

Why do you think the manufacturing process was chosen for a given component.

  • The plug was injection molded because it is the most effective efficient and economical way to produce the part. Once the mold was created it can be reused. Plastic flows easily as a liquid so it can be forced into a mold easily. This is a full production model so there are a lot of duplicates. After the part is removed from the mold the threads are cut using a die because accurate threads are hard to mold, since injecting plastic completely into the little spaces of the threads is very difficult. More precise threads can be produced by cutting with a die. Also, threads can make it difficult to remove the part from the mold.

How complex is the component?

  • Compared to the entire assembly, the plug would be somewhere towards the bottom of the scale (about a one or two), the screw or snap ring being a one, the housing being about a five and the cam shaft and bearings being an eight or nine on this scale. It has specific needs that need to be met. The tolerance of the threads is critical because they must match the placement of those on the housing. This part must prevent oil leakage while having the ability to be removed easily.

Housing Cap

This component is used only once in the pressure washer. It is made from cast aluminum; this is evident with the residual risers left on the inside of the component. It appears if the cast was made by permanent mold casting. It was then machined and six holes were drilled on the edge for the six screws that fasten the cap to the full housing. There were also two different diameter holes drilled and tapped; one for the oil drain plug and the other for a clear oil level view plug. The housing cap has cooling fins on the outside to distribute the heat built up from the pump running. There are no visible model numbers on the part.

Why were different materials chosen for different parts?

  • Different materials were selected for different components based on their responsibilities in the whole machine. Where a lot of pressure is applied a stronger metal was used to take care of these forces and not fail.

What forces are applied to the components?

  • There are multiple forces applied to the housing cap while the pump is in use. One force is the pressure on the cap from the oil pressure when the oil heats up. This force is very small and ranges with temperature but still present, probably less than a couple pounds. There are static forces on the surface where the cap meets the housing due to the tension in the six screws. This force is probably less than 100 pounds. The housing cap also experiences thermodynamic forces from heat created from friction and residual heat from the engine. Cast aluminum has high thermo conductivity so it doesn’t hold in the heat so along with the aid of the cooling fins the housing cap distributes heat to the environment quickly. The temperature probably doesn’t exceed 100 degrees Celsius.

Does the material choice affect the manufacturing process?

  • Material choice definitely affects the manufacturing process. During permanent mold casting the aluminum is melted and either poured using gravity or forced into the mold with the aid of a vacuum. After the metal is cooled the risers are cut down and the component is then machined. Aluminum has a relatively lower melting temperature making it easier and faster to cast.

Does the shape affect the manufacturing process?

  • Yes, the shape affects the manufacturing process. The cooling fins and corners of the component are round making it possible to be casted and less timely machining done. Casting is quicker for making a lot of duplicate parts which I imagine was done for this part.

Why was each manufacturing process chosen for that component?

  • The manufacturing process was chosen for this part to decrease the amount of economical cost of producing this part repeatedly. It is more sensible in many ways to cast this part and then some extra simple machining was done to make the component precise. Not as much material would be wasted compared to if the whole part was machined due to the number of cooling fins and the “odd” shape.

Do any components have a particular shape? Why?

  • The housing cap definitely has a particular shape to complete a certain task in the whole of the pump. Where the cap meets the housing there is a lip and a rubber “o-ring” of sorts to keep the flowing oil inside and not allow leaks. The drain plug was conscientiously placed at the bottom to allow easier and quicker flow when draining the oil. Also the clear oil level plug was placed in the center of the cap because that is where the level of oil should be at.

Is the component functional, cosmetic or a combination of the two?

  • The component is not only functional but is also aesthetic in some ways too. The cooling fins add a creative look to the cap and also serve the purpose of dispersing heat to the surroundings. The clear drain plug is also aesthetically pleasing but serves a major purpose in the use of the pump. If there is an insufficient amount of oil in the pump friction could increase causing an internal failure.

Why do you think the manufacturing process was chosen for a given component?

  • The manufacturing process was chosen for this part to decrease the amount of economical cost of producing this part repeatedly. It is more sensible in many ways to cast this part and then some extra simple machining was done to make the component precise. Not as much material would be wasted compared to if the whole part was machined due to the number of cooling fins and the “odd” shape.

How complex is the component.

  • This component although not very complex serves a major purpose in the pump. On a scale of 1 to 10, one being a simple screw and ten being the camshaft, the housing cap would rank about a 3 or a 4.



Connecting Spacer/ Shaft Concealer


This component is used only once in the pressure washer and connects the pump apparatus to the engine block. The spacer is made from caste aluminum. It has been manufactured by permanent mold casting. There is evidence of residual risers, there aren’t any sharp corners and all of the external cooling fins have a tapered shape. After the casting there was semi-intensive machining involved in creating this part. Both of the surfaces that contacted the engine and pump were machined to insure a perfect fit. There was machining involved to insert a plastic ring to reduce friction from the connecting shaft. Four holes were machined for connection between the spacer and pump. The main central hole was machined a lot more precise and intricate.

Why were different materials chosen for different parts?

  • Different materials are chosen because special materials are suited to perform diverse tasks. Materials were selected for different components based on their responsibilities in the whole machine. Where a lot of pressure is applied a stronger metal was used to take care of these forces and not fail.

What forces are applied to the components?

  • The forces applied to the spacer component are simple static forces. The force between the 4 screws that connect it to the engine and the 4 that connect it to the pump each would be expected to be less than 100 pounds. There is also frictional force from the shaft on the plastic ring but it is almost negligible because the plastic was added to reduce friction and not let it spin on another metal surface. This force is probably less than 1 pound. The housing cap also experiences thermodynamic forces from heat created from friction and residual heat from the engine. Cast aluminum has high thermo conductivity so it doesn’t hold in the heat so along with the aid of the cooling fins the housing cap distributes heat to the environment quickly. The temperature probably doesn’t exceed 100 degrees Celsius.

Does the material choice affect the manufacturing process?

  • Material choice definitely affects the manufacturing process. During permanent mold casting the aluminum is melted and either poured using gravity or forced into the mold with the aid of a vacuum. After the metal is cooled the risers are cut down and the component is then machined. Aluminum has a relatively lower melting temperature making it easier and faster to cast.

Does the shape affect the manufacturing process?

  • Yes, the shape affects the manufacturing process. The cooling fins and corners of the component are round making it possible to be casted and less timely machining done. Casting is quicker for making a lot of duplicate parts which I imagine was done for this part.

Why was each manufacturing process chosen for that component?

  • The manufacturing process was chosen for this part to decrease the amount of economical cost of producing this part repeatedly. It is more sensible in many ways to cast this part and then some extra machining was done to make the component precise. Not as much material would be wasted compared to if the whole part was machined due to the cooling fins and the “odd” shape.

Do any components have a particular shape? Why?

  • The spacer definitely has a very specific shape to complete its own task in the realm of the pressure washer. It is precisely 1- ¾’ to space the pump away from the engine and big enough to exactly fit the shaft in the center. The spacer has a square shaped exterior to allow for a more complete and tight connections. There are also cooling fins on the exterior to disperse the heat internally created.

Is the component functional, cosmetic or a combination of the two?

  • This component is more for functional purposes than it is for cosmetic. It functions as a barrier between the user, outside elements, and the spinning shaft. It is also some-what for cosmetic purposes because many consumers in this day and age get nervous when there is fast moving parts on machinery. This hides the shaft completely from the view of the user.

Why do you think the manufacturing process was chosen for a given component?

  • The manufacturing process was chosen for this part to decrease the amount of economical cost of producing this part repeatedly. It is more sensible in many ways to cast this part and then some extra simple machining was done to make the component precise. Not as much material would be wasted compared to if the whole part was machined due to the number of cooling fins and the “odd” shape.

How complex is the component.

  • This component, although not very complex, serves a major purpose in the pressure washer. On a scale of 1 to 10, one being a simple screw and ten being the camshaft, the housing cap would rank about a 2.


4-7mm x 24mm steel alloy allen head bolts

The function of the Allen head bolts is to fasten the spacer to the pump housing . The screws are made of steel. They are manufactured with a combination of cold rolling, forging and machining. We know this because the head of the screw is forged to give its required tool shape. It is cold rolled to give the screws their threaded shafts. It is machined in the beginning when the blank screws are sliced from the giant coil of wire.

Why were different materials selected for different components?

  • These bolts are steel alloy compared to brass because they are not in constant contact with water. It is unnecessary to use the more expensive brass screws, because the corrosion resistance is not needed.

What forces are applied to the components?

  • There are forces applied are normal and static frictional forces created when the screws are tightened.. They must hold the spacer flush with the housing without slipping, creating a tight seal. The only other forces present on these screws are vibrational forces caused by normal operation.

Does the material choice affect the manufacturing process?

  • Regardless of material, bolts are made with a combination of manufacturing processes. Beginning as a long coiled wire, the wire is cut the desired length of the screw. Next, one end of each blank is pressed and compressed to form its head. Then the shape of the tool (allen in this case) is forged into the head. Finally, the blank is cold-rolled along a harder metal form with a threaded shape giving each screw a threaded shaft. This cold rolling gives the object a high amount of strength but it sacrifices ductility.

Does the shape affect the manufacturing process?

  • Because these bolts are for the most part cylindrical, they can begin as a long coiled wire and be literally sliced into their desired lengths. Had they been another shape, a different manufacturing method would be needed.

Why was each manufacturing process chosen for that component?

  • This manufacturing process was chosen because it is the most cost effective method. It has a very low cost per screw.

Do any components have a particular shape? Why?

  • These screws have a straight cylindrical shape because that is the best shape for a screw. The threads on the end of the screw allow it to grip to its desired surface without slipping. The head is wider than the shaft of the screw because it must be able to stop the screw from spinning once it is at its desired depth into the hole.

Is the component functional, cosmetic, or a combination of the two?

  • The screw would definitely be considered more or a functional object than a cosmetic one. Its shaft is hidden and only the head is visible. The most important factor in making this screw is making it strong. Corrosion is unsightly, but was not given consideration in this part.

How complex is the component?

  • The object is itself extremely simple. It has no moving parts. In fact, it is made so that it does not move. Once it is installed, only routine tightening is needed to keep these screws performing as needed. This component forms that base of our scale, as it is the simplest part of the pump assembly. The screws have a complexity of 1 on a scale where the housing is about a five and the cam shaft and bearings are about an eight or nine.



Design Revisions:

  • It was very difficult to remove the connecting rods from the crankshaft of the pump. The connecting rod journals were press-fit onto the crankshaft In most applications, connecting rod journals have a split clamp type design that allow easy removal with two allen bolts. If our pressure washer used such a design, we would not have damaged it during the product dissection stage.
  • This pressure washer uses a reciprocating, three-piston pump. This requires many moving parts, including a crankshaft and connecting rods. In addition, all of these parts require lubrication with an oil bath. All of these factors combined to create a relatively high maintenance machine with many potential sources of friction. A possible alternative would be to use an impeller type pump. All of the moving parts inside of the pump could be replaced with a single impeller. This style of pump would not need oil lubrication and maintenance would be far simpler. If the pistons on the pressure washer wore out, it would be a difficult and time consuming job to replace them, not to mention any wear that the cylinder walls may have incurred. Changing the impeller would be a simple matter of unbolting a plate, lifting it out and placing a new one in.
  • The shaft of the water pump and the shaft of the gasoline engine are connected directly. This yields a 1:1 drive ratio. If a gear reduction was used, larger pistons could be operated at a lower speed. If the ratio of engine shaft speed to pump shaft speed was 2:1, the pistons could last twice as long. In addition, the pump would run quieter and cooler. A negative aspect of this would be the addition of more moving parts, meaning more friction and maintenance. However, the decrease in friction from the pistons would probably be significantly greater than any losses created by the gears. For proper lubrication of the gears, a separate housing would have to be created for the gears that contains oil that is heavier than what is used in the pump.

Solid Modeling:

We have chosen to model three major components of the pump assembly:

Housing:

Casing1.JPG
Casing2.JPG
Casing3.JPG

Crankshaft:

Crankshaftcad.jpg

Piston Assembly:

Materials.png
AI.JPG

Detailed video animations of the modeled components will be available here due to limitations of the wiki software: [2]

Choice of Software:

  • Our group chose Autodesk Inventor for the solid modeling portion of this project. This is a program that we as a group were most familiar with. Most of our members had used it throughout high school. In addition, Autodesk inventor is an extremely powerful package that can produce extremely precise and professional renderings. Our group was satisfied with our results.

Choice of Components to model:

  • We modeled about half a dozen very small components for the piston assembly (washer, bolt, spacer, nut, shaft, etc.). We decided to do this because these individual components were not a very big part of the pump. I made these multiple components into one assembly of the completed piston. Also, I composed an animation of the piston being put together and showing its range of motion.
  • We also modeled the crankshaft of the pump. This is one of the most important parts of the pump because this is what transfers energy from the motor to the pistons. By spinning the shaft, the pistons move up and down at a high rate of speed pressurizing the water in the manifold. We created an animation of this shaft spinning so that you can see how it rotates the pistons.
  • The final component we modeled was the outer casing portion of the pump. We made this component because it houses some of the vital parts of the pump and is that last of the major components. We went into great detail on this casing, including all of its fins, depressions and bumps.


Analysis Problem:

Problem: If the pressure washer was not winterized properly and subject to cold temperatures, could trapped water freeze and crack the wand? At what temperature could this occur?

Diagram

Fig1.JPG

Assumptions:

  • Wand is stored with upwards orientation
  • Wand is a tube with an O.D. of .500” and an I.D. of .430”
  • Wand tube is made of 304 stainless steel
  • Internal valve in handle is closed and will not fail
  • Water freezes near nozzle first and forms an immovable “plug”
  • Water is pure H?O (contains no impurities)
  • Water in the tube is at same temperature as ambient air
  • Tube will permanently deform at yield strength and burst at ultimate strength
  • Cooling process occurs slowly
  • Atmospheric pressure is constant, 1atm
  • Strength of material is constant, does not depend on temperature
  • Yield strength of 304 stainless steel is 31,200 psi, ultimate strength is 73,200 psi [1]



Governing Equations:

Strength of Pipe:

P=2S(O.D.-I.D.)/((O.D.-2T)*S.F.)

S is strength, S.F. is safety factor

Pressure and temperature of ice For 1 < P < ~2000atm, P and T are linearly related by .55?C/80atm

Calculations:

Calculations.jpg Table.jpg

The pipe will begin to deform at -6 degrees Celsius (21 degrees Fahrenheit) and burst at -14 degrees Celsius (7 degrees Fahrenheit)

Solution Check:

According to a University of Illinois study, water pipes are at risk of freezing and bursting at temperatures below 20 degrees Fahrenheit. [2] This is consistent with the results that I obtained in my analysis.

Discussion:

The temperatures at which the failures will occur seem reasonable. From personal experience with boats and RV’s, I know that pipes tend to freeze and crack at these temperatures. Ice is unique in that it is one of very few substances that expand when they change phase from liquid to solid. When ice is subject to pressure, the melting point decreases. The pressure exerted on the inside of the pipe is actually liquid water trying to solidify. The relationship between pressure and temperature of ice is linear only for a certain range close to zero degrees Celsius. This form of ice is known as “ice-I”. Ice has 13 additional forms at higher pressures and lower temperatures that vary in crystal structure [3]. I am not sure if it was necessary to assume that the ice closed off the open end of the tube by freezing there first. I included this because I thought that the expanding water would need a normal force acting on it in every direction to maintain pressure. Water used in a pressure washer would most likely be municipal or well water. Water from both of these sources contains dissolved substances and has a different melting point than pure water. When materials fail, heat is often generated (mechanical energy is converted into thermal energy). If the cooling process occurs slowly, this heat would be dissipated to the surroundings and not affect the results. Strength of materials can depend on temperature. Many materials become brittle at low temperatures. However, I could not find suitable equations to apply this.

Gate 4: Critical Design Review

Product Reassembly

  • Step 1- Piston insertion

a) Insert each of the three steel connecting rods into the three holes in the housing from the interior side of the holes located on the side wall.
b) Place large copper washers on each of the three steel studs protruding from the outside of the housing. Following this on each stud by the ceramic spacers, then small copper washer and lastly tighten the ½ in nuts on each of the piston assemblies.
4-1.jpg

  • Step 2- Pressing in the ball bearing

a) Looking at the housing from the largest open end there is a hole on one of the sides for the plastic oil plug. Orienting this hole to the top surface of the housing examine the closest orifice to the right of this hole. This will be the orifice that ball bearing resides in.
b) Using a manual/hydraulic bearing press, place the ball bearing on the top lip of the orifice. Using the press, force bearing to bottom of the cavity.
4-8.jpg

  • Step 3- Pressing in the shaft followed by roller bearing

a) From the opposite of the ball bearing, insert the small diameter end of the shaft.
b) Carefully finagle the shaft through the three circular rings (rod caps) connected to the piston assembly.
c) Once the shaft is on the verge of insertion relative to the ball bearing, press the narrow end of the shaft into the bearing using manual/ hydraulic press.
d) Using snap ring pliers attach snap ring to the small groove in the narrow end of the shaft protruding out of the center of the ball bearing.
e) Now place the roller bearing in the small gap between wide end of shaft and housing. Using a pipe of the same diameter of the bearing press the pipe forcing the bearing into the space until it is flush with the widest surface of the shaft.
4-2.jpg 4-3.jpg

  • Step 4- Fastening the ball bearing cover

a) The small square cap is the ball bearing cover.
b) Add about 1 oz of 5w-30 oil over ball bearing.
c) Place bearing cover over orifice containing the ball bearing.
d) Align the four holes with the threaded holes in the housing and use four of the twenty-two 3/16 in Allen head screws. And fasten until a half turn past snug.
4-4.jpg

  • Step 5- Fastening the shaft mounting cover

a) The shaft mounting cover is the hollow mounting shaft with two machined ends.
b) Place the shaft mounting cover over orifice containing the roller bearing.
c) Orient the side with the slotted holes away from the housing.
d) Align the four holes with the threaded holes in the housing and use four of the twenty-two 3/16 in Allen head screws. And fasten until a half turn past snug.
4-5.jpg

  • Step 6- Fastening the housing cover

a) The cover with the metal drain plug and clear oil plug is the housing cover.
b) Place the housing cover over the final opening to which you can see the shaft through.
c) Orient the housing cover so that the six holes align with the six threaded holes in the housing and use six of the twenty-two 3/16 in Allen head screws. And fasten until a half turn past snug.
4-6.jpg

  • Step 7- Fastening the brass manifold

a) Align the three holes in the bottom of the brass manifold with the three pistons projecting from the housing.
b) Slowly slide the manifold onto the pistons until it is fully contacting the housings.
c) Using the remaining eight 3/16 in screws, fasten the brass manifold to the housing. Fasten the screws until a half turn past snug.
4-7.jpg

Does your product run the same as it did before you disassembled it?

We were unable to determine if our product ran or not because our product, a pressure washer, was shared between multiple groups. Our group concentrated on the water pump and did not have access to the entire machine. During the disassembly process, we observed that all of the internal components were in good condition. Therefore, we assume that the pressure washer was in good working order. Unfortunately our group made a mistake that caused damage to some of the internal components. We managed to break all three of the connecting rod journals when we tried to remove them from the crankshaft of the pump. The pressure washer is no longer operational. To restore the pressure washer to a working state, the broken parts would have to be replaced. Repairing these parts would be nearly impossible due to the tight tolerance required on their inside diameter.

What were the differences between the disassembly/reassembly processes?

Our group encountered many problems during the disassembly process of the pressure washer pump. However, no problems were encountered during the reassembly process. We completed reassembly in a fraction of the time it took for disassembly. When we disassembled our compressor we were not entirely sure how it came apart. Each component presented a new challenge to our group. We were unsure of what certain components did and what tools were required to remove them. We encountered several press-fit parts that required us to use tools that we were unfamiliar with. Removing each component required the group to make several decisions which took a considerable amount of time. At one point our group was faced with the decision of how to remove the connecting rods from the crankshaft of the pump. Each group member gave his input from past experience and we even consulted outside help. After some debate, our group reached a consensus, which turned out to be incorrect. During the reassembly process, our group was able to review the notes we had taken during disassembly, which greatly reduced the difficulty and time required. We were not required to make the decisions that made the disassembly process so challenging. All the same tools were used to reassemble the product as were used to disassemble it, namely, a set of Allen wrenches, a bearing press and a pair of snap ring pliers. Due to the fact that we broke three components during disassembly, we were not able to reassemble our entire product. Had we not broken these components, including them in the reassembly would not have significantly increased difficulty or time required.

Are there any additional comments your group would make at the product level?

We would like to suggest that the connecting rod journals in the water pump be of a split-clamp design as opposed to the solid hoop design that used by the manufacturer. This modification would make the disassembly of the product much easier in the case that the pump became clogged with debris or internal components needed replacement. Instead of having to use a bearing puller, the journals could instead be removed with two allen bolts.

References