From DDL Wiki
The keg tap shown above was analyzed in order to determine its functionality, ease of assembly, and design weaknesses. The first step in this process was product dissection. This step enabled us to determine the functionality and create a detailed bill of materials. We were able to break the tap down into 22 parts and 3 sub-assemblies.
The next step in the analysis was user testing. By going through the entire process of purchasing a keg, placing it in an ice-filled container, and tapping it, we were able to determine several areas of design weakness that we would not have been able to foresee simply by looking at the tap. While the leading complaint was foamy beer, other issues included ergonomics, dealing with bulky ice bags, and only having one outlet to dispense drinks.
After the user study, we ran three different analyses: Design for Manufacture and Assembly (DFMA), Failure Modes and Effects Analysis (FMEA), and Design for Environment (DFE). The purpose of the DFMA was to assess how well each part is manufactured and assembled. We found that while the keg tap is generally well designed, possible improvements include standardizing part size and materials and decreasing the amount of machining needed for metal components by considering alternative processes such as metal injection molding or casting. A bonus to this particular design is that most parts are attached with threaded connections, making disassembly for cleaning and repair possible.
The FMEA was run to in order to assess the likelihood of each individual part failing. A detailed chart was made describing the possible failure modes for each part. It was ultimately found that some of the geometries used in the parts making up the tap increase the amount of turbulence, leading to more foam. A possible redesign of the tap would allow for some more laminar friendly geometries.
The purpose of the DFE analysis was to see how each part of the manufacturing process contributes to greenhouse gas emissions. From this, it was found that the largest component of greenhouse gas emissions associated with our product is beer manufacturing. A large amount of foam is produced in the transport and distribution of the keg and is discarded by the user. Therefore, if we reduced the foam created and in turn beer wasted, the environmental impact associated with the beer manufacturing sector would also be reduced.
Finally, we did a mechanical analysis in order to determine if the flow of beer is laminar or turbulent, with the general idea that laminar flow will mean less foam. It should be noted that while the objective is to obtain a laminar flow, we realistically will only be able to get close. Thus, the chances of totally eliminating the necessary foam is not very likely. So, after doing some fluid mechanics calculations, we found the Reynolds number of the tube to be 6430, showing turbulent flow. This flow can be achieved by either having a wider tube/nozzle or reducing the speed at which the beer flows.
By taking into account all of these analyses along with the needs of the various stakeholders, we have found that there is plenty of room for improvement in the design of the keg tap. Reducing cost, waste, and environmental impact along with making it more of a multi-functional, ergonomic product are all goals for the redesign phase.
Major Stakeholders and Product Needs
For this product there are two types of consumers: the people that will buy and own their own tap, and those that will rent their tap from the beer distributor. Since renting and owning your own tap create slightly different concerns from the consumer, we have assumed that everything the renters want are encompassed in a larger list from what the owners will want. Therefore the following list will describe what is important to the owners of taps.
- Limit foam
- Small and lightweight for storage
- Ease of storage
- Replacement parts
- Cold beer
- Fast service
Retailers and beer distributors are both looking for the similar things from their taps. The following list encompasses what they are both looking for in a tap.
- Cheap materials
- Durable materials
- Returns a profit
- Ease of storage
- Ease of cleaning
- Replacement parts
Manufacturers basically want to be able to create your parts needed as quickly and cheaply as possible. That in mind these are some things manufacturers want in the tap design.
- Limit parts
- Limit different materials
- Limit materials
- Limit manufacturing processes
- Cheap manufacturing processes
- Ease of assembly
Lastly the companies that transport our product from place to place will want certain things from the product as well.
- Sturdy, not easily broken
- Small packages
- Many shipments
How it's used
Tapping a keg requires 2 things: a keg tap and a keg of any size. The purpose of the keg is to store the beer, and the purpose of the tap is to release the beer from the highly pressurized keg (Figure 1). There are basically 6 steps.
- Place the keg in a container full of ice. Since transporting the keg often creates a lot of foam, it is a good idea to let the keg stand for a while so that some of the foam can settle.
- Remove the cap from the circular opening on top of the keg.
- Place the tap above the keg opening with the lever in the upward position, as shown in Figure 2.
- While pushing down, twist the base clockwise into the grooves of the keg opening (Figure 3).
- Once it is twisted as far as it can go, push the lever down. This locks the tap into place and creates a space for airflow into the keg (Figure 4).
- Push pump up and down 3-4 times while simultaneously releasing beer into a cup (Figure 5). The beer is released by holding down the small handle on the end of the hose.
Although tapping a keg is a relatively simple process, there are many ways in which it can be misused. One common mistake is forcing the tap into the opening with the lever already down, which causes beer to spray up. In the above steps the twisting of the tap into the keg creates an air tight seal. The further step of pushing the lever down then opens the keg up allowing beer to flow from the keg into the tap, through an air tight seal, and to the user's cup. If the lever is down while you are twisting the tap into the keg, you are opening the keg without an airtight seal, allowing beer to escape around the edges of the tap base. Another common mistake is pumping too frequently, which causes the beer to become really foamy (See Figure 5). The fact that it is not entirely obvious how it should be used is in itself a potential design flaw. Having never tapped a keg before, it took us quite a while to figure it out, and even when we had gotten it attached properly, we still managed to over-pump the tap, causing the beer to be foamy for the entire night.
Even with a properly tapped keg, there were still many responses from users, indicating a lot of room for improvement. General feedback is as follows:
- Beer is still foamy.
- For girls especially, it was difficult to lock the tap into place due to the amount of force it requires.
- The bulky ice bag is heavy and creates a mess, and often it's hard to find a suitable container to hold the keg with the ice.
- It is difficult to keep the keg cold for a long period of time.
- While a full keg contains approximately 165 beers, there is still only one outlet, which means there is often a long wait to fill up a cup.
- The ball on the end of the plunger could be more ergonomic. After several pumps it caused hand pain.
From these comments, it is clear that the biggest issue is foam. If the pressure could somehow be regulated so that it prevented people from over-pumping the tap, this would be ideal. Taking it a step further, if the initial foam caused by shaking the keg during transportation could be somehow reduced using some extra function of the tap, this would be even better. Other, less-burdensome ways to keep the keg cold, better ergonomics, and a multiple hose tap are all possibilities that should be researched for the redesign.
Bill of Materials
As shown in the table below, the keg tap analyzed in our study has 27 unique parts, with 3 sub-assemblies. The plunger, hose, and the nozzle all have multiple parts, all of which are clearly visible. The parts range from 0.05 to 7.2 oz and are made of either steel, brass, rubber, or plastic.
The o-rings, nut, washer, and lever pin are all standard purchase parts.
Keg Tap Components
Due to the fact that the center cylindrical pieces all having threading, the parts can easily be disassembled and put back together. The assembly procedure is as follows:
- Slide all 4 O-Rings (Part Numbers 3, 5, 9, and 19) onto the Parts 2, 4, 8, and 18, respectively.
- Slide the spring (7) and the cylindrical top (6) onto the plunger (2) in the order shown.
- Screw the Black Ball handle (1) onto the plunger assembly just described.
- Put the plunger (2) into the cylindrical plunger casing (4), and screw the top on tightly.
- Push the base (18) onto the center cylinder (8) and then screw the center cylinder onto the plunger assembly.
- Push the white cap (12) into the end of the lever casing (11).
- Line the lever assembly (10) up with the hole on the base (18) and slide the lever pin (17) through the hole and screw it into place.
- Push the nozzle seal (22) onto the nozzle assembly (21) and then screw the nozzle onto the end of the hose (21).
- Screw the threaded end of the hose (21) into the hole on the side of the center cylinder (8).
The tap is attached to the keg by twisting the base (18) onto the top of the keg; once the base is screwed on, the lever (10) is pulled out so its center rod (14) slides out of the groove in the base. The arms of the lever sit in two cuts in the center cylinder. Lifting the lever causes the lever arms to slide in the cuts, forcing the cylinder down and engaging it with the keg.
The keg itself is constructed with a tube that runs down the center to draw the beer up. Its top has an embedded valve into which you press the base of the keg tap. The valve allows air to enter the keg when the tap is pumped. The air that is pumped in increases the pressure in the keg and forces the beer up the center tube.
When the user pulls the tap handle (1) up, air is drawn into the cylindrical plunger casing (4) through two small holes in the plunger disc (2.1) below the o-ring (3). The handle is then pushed down, expanding the o-ring and sealing the holes in the disk. The air in the plunger casing is forced through the center cylinder (8) and into the keg, pushing beer up the tube into a separate section of the center cylinder. From the center cylinder, the beer flows through the hose (20) up to the nozzle. When the nozzle handle (21.1) is pressed down, the plastic center (21.2) pulls up on the nozzle seal (22), releasing beer from the hose. A diagram of the air and beer flow between the tap and the keg is shown below.
Design for Manufacturing and Assembly (DFMA)
The purpose of Design for Manufacturing and Assembly (DFMA) is to highlight opportunities for improvement through changes to the manufacturing process and assembly of the product. Some important points to consider are material choice, cost, production volume, part count, and tolerances.
This particular keg tap consists of 29 distinct parts. The non-metal components are made from plastic and rubber, and for the most part are manufactured via injection molding. One potential improvement for the manufacturing of the non-metal components is the o-rings. There are four o-rings in the keg tap, all of which are different sizes. This is a potential problem for consumers. The tap is manufactured so the user can take it apart, and it would not work correctly if the o-rings were mixed up and placed in the wrong locations when reassembled. Also, o-ring fatigue is one of the most likely causes of failure; if users are replacing o-rings somewhat regularly, it would be convenient to only order one standard size.
The majority of the metal pieces are made from stainless steel, with the exception of three interior components that are made from brass. The reasons for making a few pieces brass are unclear, though it may be because of the material's antimicrobial properties <ref>http://www.copper.org/antimicrobial/homepage.html</ref>. Again, one could improve the manufacturing of this product through standardization, this time of materials. Stainless steel could be used to make all the metal components.
All of the metal components are shaped using a deformation process except for the base and lever, which are cast. Casting is a logical manufacturing choice for the base because of its relatively complex shape. The other main metal parts are extruded, then machined. Machining includes removing material with a lathe or milling machine, drilling holes, cutting threads, and grinding down sharp edges. The amount of machining involved in the manufacturing process is acceptable for this product because it is intended for medium volume production. If the target market increased in size or changed demographics, the current manufacturing processes would have to be reevaluated. An increase in market size would make machining individual parts infeasible. This problem could be solved by either redesigning the tap to have less components, or switching to a process more suitable to high volume production, such as metal injection molding. A change in market demographics, such as a shift in sales from middle-aged beer connoisseurs to college students, would call for a change in the price of the keg tap. This could be achieved by switching to a casting process for more parts; the overall aesthetics might not be as pleasing, but machining costs would go down.
Another way to decrease manufacturing costs is to make more components out of plastic. Plastic injection molding is cheap and fast, at least for high volume production, and produces components lighter than the current metal parts. Injection molding also allows for more freedom in the structure of the tap, since parts are shaped in the mold and not machined. Downsides to increasing the number of plastic components include durability issues and the potential for plastic flavor leeching into the beer.
The keg tap is relatively easy to assemble. All parts are joined by threads or snapped on (o-rings); if given a reference, the average person would be able to put the parts together. This saves machine cost in manufacturing, but increases labor cost. The current joining methods are convenient for the consumer because the tap can be disassembled for cleaning and repair; if an o-ring broke, you could replace it instead of buying a whole new tap.
Overall, the producers of this keg tap have designed carefully for both manufacturing and assembly. The few improvements that can be made involve part standardization and possibly a change in the manufacturing of metal components. The change in manufacturing would only be sensible if the target market increased in size.
Failure Modes and Effects Analysis (FMEA)
Failures modes and effects analysis is a tool that we have used in order to spot weaknesses in our competitors design, as well as the strengths of their design. After an in depth look at every part in the keg tap we have come to multiple conclusions. First of which being that the design of the tap in many ways was made to withstand much larger forces and pressures than it should ever see during normal and in most cases abnormal use. Secondly, our competitors design showed a slight weakness in the use of its o-rings. Lastly, a large weakness of our competitors' design was the amount of foam the user got in their cup versus beer.
From the following table it is easy to see that many of the components of the tap have very low RPN's. This shows that the design of those parts is already robust enough that there is no need to change them. For example the plunger has a rod made out of 3/8" diameter stainless steel. The rod could be made smaller than that while still allowing the tap to function. Though this may save material cost it is most likely not worth it to go smaller in diameter.
Its true that our competitor also showed a slight weakness in using o-rings though it would be much more expensive to attempt to get ride of them. O-rings allow the tap to be made into multiple sections. They allow those sections to be connected by simply screwing them together and adding an o-ring in between to maintain an air tight seal. Therefore, the higher RPN values caused by o-rings will allow for a much cheaper product while still maintaining a device that will work for a long time.
Lastly, the part of the project our team is going to work to solve. FOAM! Some parts of the tap have geometries that help in the creation of foam. There are some tight clearances and sharp turns in the center cylinder which help make the flow of the beer turbulent, introducing more foam. Our group has concluded that with some slight changes to this piece and some of the connecting pieces we may be able to cut back on the ratio of foam to beer the user receives while using our product.
|Part #||Item||Function||Failure Mode||Effects of Failure||S||Cause of Failure||O||Design Controls||D||RPN||Recommended Actions|
|1||Black Ball||Grip for Pumping||Could be Unscrewed and Lost||Uncomfortable Pumping||4||Unaware Users||1||Make sure the ball is screwed on tightly||1||4||Apply Loctite|
|2||Plunger||Forces Air into Keg||Could be snapped off while locked into keg||Unusable||7||Unaware Users||1||Increase diameter||1||7||Be careful!|
|2.1||Plunger Disc||Air Tight||This part is very robust. Cannot foresee any failure modes.||---||-||---||-||---||-||-||---|
|3||Plunger O-Ring||Seal||O-ring becomes hardened||Loss of air tight seal for pressurizing keg||3||Repeated use and time||2||Oil the o-ring||5||30||Sell spare parts|
|4||Cylindrical Plunger Casing||Supply Keg with Pressure||Dent in the casing, burs, scratches, rust on the inside of the casing||Plunger cannot be moved inside the case, o-ring gets torn up||7||Misuse, Dropping the tap||1||All these pieces are robust enough||1||7||None|
|5||Cylindrical Casing O-Ring||Seal||O-ring becomes hardened||Loss of air tight seal for pressurizing keg||3||Repeated use and time||2||Oil the o-ring||5||30||Sell spare parts|
|6||Cylindrical Top||Encloses Plunger in Casing||Top comes unscrewed||Cannot pressurize keg||1||Human tampering||4||Check that it is screwed on tightly||2||8||None, gluing these threads makes disassembly harder|
|7||Plunger Spring||Prevents Plunger from Getting Stuck||Breaks||Plunger, though unlikely, may get stuck at top of casing||7||Misuse or fatigue||1||Make sure spring can handle forces||1||7||Sell spare parts|
|8||Center Cylinder||Separates Air Input from Beer Output||1)Leaks beer at the connection point with hose
2)Creates turbulence in beer flow
|1)Loss of beer
|7||1)Sealant on threads is old
|7||1)Check that their are no leaks
2)Look into some other way to transition into tubing
|9||Center Cylinder O-Ring||Seal||O-ring becomes hardened||Loss of air tight seal for pressurizing keg||3||Repeated use and time||2||Oil the o-ring||5||30||Sell spare parts|
|10||Lever||Attaches Tap and Keg allowing the flow of beer||This part is very robust. Cannot foresee any failure modes.||---||-||---||-||---||-||-||---|
|11||Lever Casing||Grip for user||Breaks||Unable to attach tap to keg||7||Ridiculous Misuse||2||Make sure the part is strong enough||1||14||None|
|12||White Cap||Aesthetics||Could break or get lost||None||1||Misuse or overuse||2||Check this fit||1||2||None|
|13||Lever Spring||Helps lock tap in two certain positions||Impact fatigue||Unable to lock tap into open position on keg||7||User misuse||1||Make sure spring can handle forces||2||14||Brainstorm new ways to lock tap|
|14||Center Rod||Helps hold handle together||This part is very robust. Cannot foresee any failure modes.||---||-||---||-||---||-||-||---|
|15||Nut||Helps hold handle together||Could come unscrewed||Unable to use tap||7||Repeated use||1||Make sure it is screwed on the whole way||1||7||None|
|16||Washer||Helps hold handle together||Cannot foresee any failure modes||---||-||---||-||---||-||-||---|
|17||Lever Pin||Attaches the lever to the base and acts as a pivot point for the lever||No foreseen failure modes.||---||-||---||-||---||-||-||---|
|18||Base||Attaches to Keg||Threads become crooked||Unable to connect tap to keg||7||Terrible misuse||1||Threads are very robust||2||14||Sell spare parts|
|19||Base O-Ring||Seal||O-ring becomes hardened||Loss of air tight seal for pressurizing keg||3||Repeated use and time||2||Oil the o-ring||5||30||Sell spare parts|
|20||Hose||Transfers Beer from Tap to Cup||1)Hole
|1)Beer is lost
2)Beer cannot reach its destination
|7||1)Not taking care of tap
|1||Make sure the tubing is the right kind||2||14||None|
|Releases Beer from Hose||Failures will follow from individual parts||---||-||---||-||---||-||-||---|
|21.1||Handle||Allows the user to start and stop the flow of beer||Deform/Break||Beer would not be allowed to come out the nozzle||7||Pushing the handle past where it should be||1||Use thick enough plastic||1||7||Sell spare parts|
|21.2||White Plastic Center||Connects nozzle handle to cap seal||Connection point to nozzle handle breaks||Beer can not come out of nozzle||7||Pushing the handle past where it should be||1||Test to make sure it operates the way it should||1||7||Sell spare parts, look for a possible redesign|
|21.3||Spring||Apply extra force to keep the pressurized beer from coming out of the keg||No foreseen failure modes||---||-||---||-||---||-||-||---
|21.4||Hard Plastic Cap||Connects the Handle to the nozzle||Fracture||Nozzle/Handle would not be able to function||7||Over tightening the cap onto the nozzle||1||Tighten cap enough so users do not have to||1||7||Sell spare parts|
|22||Nozzle Seal||Blocks the flow from leaving the hose||Surface fatigue wear||Beer would leak through and leave the nozzle||7||Repeated use||1||Make sure the rubber used can withstand many cycles||1||7||Sell spare parts|
Design for Environment (DFE)
DFE is used to determine the environmental impact a product has on its environment. Engineers usually use life cycle assessment(LCA) to put a number on how much a product impacts the environment. LCA traditionally studies each process in producing, transporting and using a product taking special note of emissions and waste.
We performed our LCA by using an online computer program that calculates the product's impact via an Economic Input-Output LCA (EIO-LCA). This tool looks at the business sectors in which your product most closely fits and compares sector averages to describe the entire supply process. After looking through all the relevant sectors we decided that the Miscellaneous fabricated metal product manufacturing sector fit our product the best. Even though our product is not specifically named, we feel its a good match because many other products are similar to ours.
- Greenhouse Gas Emissions
When an additional 1 million dollars is spent in the Miscellaneous fabricated metal product manufacturing sector, greenhouse gas emissions rise by approximately 796 metric tons of CO2 Equivalent (MTCO2E). The data shows that the majority of the gases are produced by power generation and supply, iron and steel mills, and transportation. The actual sector that produces the tap only produces 42.6 MTCO2E, which is small considering the amount released in other sectors.
- Toxic Releases
An additional 1 million dollars spent in the sector for keg taps results in a rise in total toxic releases of 1590kg. The primary contributors to these releases are mining of: copper, nickel, lead, and zinc gold, silver, and other metal ore mining. The Miscellaneous fabricated metal product manufacturing sector only amounts to a 57.1 kg increase in toxic releases.
Using the template of Professor Michalek's "EIO-LCA example: coffeemaker" we did a comparison of the emissions associated with the use of the product versus the manufacturing of it. Since the keg tap itself is manually operated the power input is not applicable, but there are other products that are used with the keg tap. Foremost, is beer from a keg and we assumed that this product would be used to the extremes, like a fraternity would use it. We decided this too see what the maximum impact would be of using 520 kegs over a 5 year lifetime window. Secondly, solo cups are a necessity so we included them as well, assuming 100 cups used per keg.
Based on the data above, it is clear that the manufacturing of our tap has next to no environmental impact compared to the manufacturing of plastic cups and especially to the brewing process.
End of life
Our product is composed of only metal and plastic, both of which can be recycled. The likelihood of the tap getting actually recycled however, just like anything, is questionable. One way to possibly encourage this would be to place a recyclable logo on the design. Once it can no longer be used, there are a few ways to recycle it. Some parts are almost impossible to break and can be used again as is and just reassembled with parts that needed to be replaced. The pieces that break can be melted down and reused in some way, whether they are plastic or metal.
Based on the numbers provided in the figure above it would be wise for our group to emphasize reducing wasted beer because it is the largest component of greenhouse gas emissions associated with our product. A large amount of foam is produced in transport and distribution of the beer in a keg and it is normally thrown away. If we could reduce the foam created we could in turn reduce the environmental impact that our product is associated with.
There are 2 different mechanical analyses that we did on the keg & tap system. The first is to determine how much the keg pressure increases per pump, which in turn would increase the pressure in the hose. Secondly, since our system is composed of fluid flowing through tubes, we can determine if the beer is flowing in a laminar or turbulent fashion by finding the Reynolds number. Both of these analyses relate to the amount of foam dispensed, which is a major design issue that we are looking to address. Specifically, over-pumping causes an increased pressure, forcing the beer up into the center cylinder of the keg and creating foam. This phenomenon was experienced during user testing and is a common source of error. Turbulent flow also creates foam, and this is something that can be understood intuitively. Just as turbulent water creates waves, turbulent beer will create more foam.
The numbers calculated make sense because as the beer level decreases in a keg, the more pumps it takes to keep it at the necessary pressure. As the keg approaches empty, it takes an almost constant pumping in order to maintain constant flow of beer. However, in the beginning it takes considerably less pumps for the same pressure.
Since our Re is greater than 4000, it is clearly turbulent. However, the number is not many orders of magnitude higher so it is possible to reduce it to a transient or ideally a laminar flow. Laminar flow would reduce the amount of foam created in the tube while it's being poured. This can be achieved by either having a wider tube/nozzle or reducing the speed at which the beer flows.
Team Member Roles
Dan Boljonis: DFE, Mechanical Analysis
Keith Haselhoff: FMEA, Stakeholders
Abby Morrell: BOM and Diagram, FBD of Mechanical Analysis, Usage, Summary, Participant in User Study
Julia Weirman: DFMA, BOM, Mechanical Function, Participant in User Study