Bilge pump

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This product is a component of the analysis for the aquarium pump project.


Product Purpose

The primary purpose of a bilge pump is to remove water from a maritime vessel. However, the pumping function of the device makes the hand-operated version useful in a range of applications where a liquid must be drawn out of a source and relocated to a different area. Although the use of a device to remove accumulated water from a boat evolved from buckets, to hand-operated bilge pumps, and finally to electric bilge pumps, the hand-operated version of this technology is widely used on vessels as a backup in the event of an emergency. In addition to small boats, hand-operated bilge pumps are used in kayaks, canoes, rowboats, lifeboats, and a host of other personal watercraft applications in which a compact, light-weight, easy to use, and economical pump is required.

Customer Needs

The principal user needs for a hand-operated bilge pump (as used in its original design context) are as follows:

  • Ability to pump large quantities of water in a short period of time
  • Compact shape to facilitate storage (especially in the cramped confines of a kayak or canoe)
  • Light-weight design for convenient travel
  • Ease of use
  • Durability (to withstand common use and wear)
  • Low cost (to encourage widespread use)


As entities (either individuals, businesses, or groups) that have some degree of dependency on the product, the following entities are possible stakeholders for the bilge pump:

  • Users
  • Designers, engineers, managers, and other employees at company where product is made
  • Suppliers of raw materials
  • Boating, sporting goods, and outdoor stores

Consumer Demographics

In its original design context, the primary users of this product are individuals who participate in maritime activities in a small vessel or personal watercraft. However, the hand-operated bilge pump can be employed in other settings as well, which would suggest that the targeted demographic could change depending on the application of the device. For instance, if the pump is being modified to empty an aquarium, fish-owning individuals would become the new primary consumer demographic.

Product Function

The functions that allow hand-operated bilge pumps to draw water from a source and deposit the water to another location are relatively straightforward. The rubber flap located at the base of the pump allows water to flow in a unilateral direction away from the removal source. Simultaneously, water pressure forces open a sliding disk valve near the bottom of the moving piston, which allows water to enter the upper portion of the cylinder. For the upstroke of the device, the aforementioned disk valve of the piston is forced closed. The water is concurrently drawn out of the top of the device (typically into a hose that is connected to the water disposal area), while the flapper valve simultaneously opens. During this stage, the pressure differential between the atmosphere and the low-pressure section of the lower cylinder causes water to be sucked into the device from the original water source.

Product Use

In order to demonstrate the use and workings of the pump, our group made videos that illustrate the following product functions:

  • Complete Bilge Pump Demonstration: This video demonstrates the function of a bilge pump in the application of evacuating a bucket into a nearby sink. Note how more liquid is pumped on the upstroke of the plunger than on the downstroke.
  • Partial Bilge Pump Demonstration: This video illustrates the internal movement of the plunger inside of the bilge pump shaft. Note the tight seal between the plunger and the yellow shaft.
  • Plunger Demonstration: This video shows the internal workings of the bilge pump by demonstrating how the plunger draws water into the bilge pump shaft and draws the water out of the top of the device.

In addition to the use of the bilge pump, cleaning and storage are important components of the product's design. Cleaning the outside of the product is facilitated by the smooth plastic surface material that allows one to wipe off solid and liquid residues easily. It is likely that the manufacturers assume that the inside of the device will not need to be cleaned often, as the glue that permanently holds the shaft together renders taking the device apart for cleaning purposes virtually impossible. This assumption is substantiated by the fact that the liquid being pumped with the device most often is ordinary water from a river or lake. Any minor buildup of sediment inside the pump could likely be flushed out by running tap water through the device.

In terms of storage, this device's slim design and light weight make it an ideal fit for any kind of small nautical vessel. The bilge pump's functionality (i.e., its ability to pump large quantities of water in short periods of time) is balanced with its storage considerations, allowing the pump to be clamped around the shaft to the vessel or to fit nice inside of an outdoor pack for travel.

Bill of Materials

Part Number Description Quantity Function Material Weight Manufacturing Process Image
1 Handle 1
  • Moves inner shaft and pluger/seal to operate pump
Blue Plastic 1.6 oz Injection Molded
Rivets 2
  • Secures attachment from handle to shaft
Aluminum Machined
2 Shaft 1
  • Functions as main outer casing for fluid, holds plunger in place, and permits fluid movement through cavity during pump operation
Yellow Plastic 3.7 oz Extruded
3 Screws 2
  • Attaches water exit sprout and end cap/water entrance pieces to outer shaft (in addition to glue)
Aluminum <0.1 oz Machined
4 Water Exit Spout 1
  • Holds handle/plunger place and allows an exit for fluid
Blue Plastic 1.9 oz Injection Molded
5 End Cap/Water Entrance 1
  • Houses flapper
Blue Plastic 1.1 oz Injection Molded
6 Flotation Device 1
  • Allows to device to float
Foam (with Blue Plastic Coating) 0.7 oz Spray Casting
7 Plunger Shaft 1
  • Attached to plunger/seal and handle
Black Plastic 2.0 oz Extruded
Plunger Cap 1
  • Holds plunger in place
Blue Plastic Injection Molded/Machined
Plunger 1
  • Forces fluid to move in and out of pump cavity when handle is pushed/pulled
Thin Rubber Polymer Synthesized
8 Flapper 1
  • Allows water to only flow into device and blocks fluids from flowing out of entrance opening
Thin Rubber 0.1 oz Polymer Synthesized

Note that the plunger cap and plunger could not be removed from the plunger shaft during the product dissection. These two parts were joined to the assembly with a very strong glue. Although acetone was used in an attempt to dissolve this glue, the plastic components of the bilge pump began to dissolve instead. The flapper was attached to the end cap by two small plastic posts over which the two flapper holes snugly fit. Thus, one side of the flapper was fixed in place, while the other was able to open and close freely with the motion of the water.

Failure Mode and Effects Analysis (FMEA)

The table below details our assessment of the most common failures that we anticipate the bilge pump to experience. This assessment explains how product parts may fail and what the consequences, detectability, and probability of occurrence those failures implicate. Addressing these possibilities will allows future designs of this product to be more reliable. Using the Suggested Evaluation Criteria (as found on the FMEA wiki page), we were able to rank the severity from 1-10 (10 being the highest). For the occurrence parameter, we then were able to rank the probability of failure again from 1-10 (with 10 being the highest). Finally, we were able to rank detectability from 1-10 (with 1 being the most detectable). From these three numbers, we were able to multiply them together, which results with the Risk Priority Number (RPN).

Item and Function Failure Mode Effects of Failure S Causes of Failure O Design Controls D RPN Recommended Actions Responsibility Actions Taken S* O* D* RPN*
  • Moves inner shaft and plunger/seal to operate pump
Breaking Pump will no longer operate 8 Shearing at rivet locations due to excessive forces or stresses 2 Use strong plastic in handle, especially near rivet locations 1 16 Strength tests before release of product, upgrade of material if necessary Materials Engineering/Manufacturing Engineer - - - - -
Inner Shaft
  • Attaches to plunger/seal and moves up and down by handle to move fluid
Breaking Pump will no longer operate 8 Forces or stresses applied in an incorrect direction (i.e., applied perpendicular to the direction of the rod) 5 Use thick walled, strong plastic to make inner shaft 1 40 Strength tests before release of product, upgrade of material if necessary Materials Engineering/Manufacturing Engineer - - - - -
Outer Shaft Cavity
  • Fluid pulled into cavity and is moved through volume during pump operation
Clogging Pump will operate less efficiently and could lose all function 5-8 (depending on level of clogging) Sediment buildup, insufficient room for larger objects drawn into the pump such as debris/garbage 7 None 3 105-168 Addition of a grate at entrance to pump cavity that will keep out large sediments or debris Design Engineer/Manufacturing Engineer - - - - -
Rubber Flapper
  • Allows fluid only to enter pump and blocks from flowing out of entrance opening
Breaking/Tearing Fluid able to exit cavity through the entrance - Pump fails to operate 8 Rubber tears due to excessive use, or high forces from fluid or debris, or extreme conditions such as heat 3 None 1 24 Thicker rubber in area of attachment to prevent tearing in this area Materials Engineer/Manufacturing Engineer - - - - -
Rubber Seal (Plunger)
  • Forces fluid to move in and out of pump cavity when handle is pushed/pulled
Wear Pump will lose efficiency 6 Thin rubber at edges wear down due to excessive use or forces 6 None 5 180 Make pump easier to disassemble and inspect Design Engineer/Manufacturing Engineer - - - - -
Tear or breaking Pump will lose efficiency or fail to operate altogether 6-8 (depending on severity of tear) Rubber tears due to excessive forces caused by fluid or debris 3 None 2 36-48 Make pump easier to disassemble and maintain Design Engineer/Manufacturing Engineer - - - - -
All Plastic Parts Corrosion Wearing of plastic, decrease in strength of parts and possibly pump efficiency 4 Plastic deteriorates due to contact with corrosive fluids 2 None 1 8 None - - - - - -

The highest RPN value for this analysis was 180, which ended up being the rubber seal losing efficiency. This failure received a 6 for severity, a 6 for probability of occurrence, and a 5 for detectability. The result of this failure would be the pump operating inefficiently or possibly not at all. From this analysis, it can be concluded that even the most catastrophic failure is not detrimental to the user with respect to his or her physical safety and wellbeing. The worst case scenario would lead to the pump losing its functionality, which may causing the user to have to purchase another such pump. This analysis also shows that there is minor room for improvement.

Design for X (DFX)

The concept of DFX refers to considering a specific variable X in the design of a product. Some common variables that are considered are ease of manufacturing, assembly, use, and maintainability.

Design for Manufacturing and Assembly (DFMA)

DFM and DFA refer to analysis and design strategies that aim to understand how a product is made and how the manufacturing and assembly steps in its production can be improved. The DFMA process is advantageous for a designer's consideration due to the tremendous cost benefits that accompany the simultaneous analysis of DFM and DFA and the interface between the two methods. The use of these methodological tools can reduce costs, decrease labor, cut production times, decrease part counts, and improve the overall design quality.

Design for Manufacturing (DFM)

The primary goal of the DFM process is to analyze the manner in which the component parts of a product are made. By examining how things are manufactured, this process can be optimized so that parts can be produced efficiently and economically while adhering to design constraints. In order to optimize a manufacturing process, cost factors must be taken into account along with time, labor, environmental, and quality concerns. The list below details some ways that DFM could have been or could be applied to the bilge pump:

  • Outer and inner shafts are both extruded, which allows for less wasted plastic and ultimately greater efficiency and lower cost in mass production
  • Handle, entrance nozzle, exit nozzle, and plunger cap all were injection molded, meaning that almost no material was wasted and the parts were complete after this step leading to lower manufacturing costs and efforts
  • Product contains few materials that are difficult or expensive to manipulate in manufacturing process (e.g., rubber, glass, metal)
    • Some rubber is necessary as a flexible yet durable material is necessary for both the flap and the plunger/seal

The analysis above suggests that the product has been designed well for manufacturing. The bilge pump design reduces manufacturing costs through its choice of materials, and the usage of plastic for most parts also makes the product durable and useful in its given functions. Also, since a requirement for this part is that it is light so that it can be made to float, the choice of plastic fills this function as well.

Design for Assembly (DFA)

The objective of DFA is to improve product quality and reduce costs by optimizing a product’s design and assembly process. DFA goals are predominantly achieved through simplifying a product, reducing part counts, and designing components that can be easily managed and installed. The follow list describes how DFA may have been or should be applied to the bilge pump:

  • Product design uses sleeve fitting however some fasteners are still used that are most likely unnecessary and should be eliminated
    • Tools could also be eliminated if fasteners such as screws and rivets were eliminated
  • The sleeve fitting used to attach the plunger/seal to the inner shaft using the plunger cap is a good design and makes assembly more efficient
  • Parts are easy to handle and fit together in a logical order
  • No two parts are identical so it is easy to keep parts separate and use them appropriately
  • The glue used to create a seal between parts with sleeve fittings is likely unnecessary and requires time for application and drying during the assembly process
    • Maintaining the product would also be made possible if glue was not used to create a seal between parts

From the above analysis, it is clear that there are several steps that could be taken to improve the assembly process used to fabricate the bilge pump. Because sleeve fittings are used between most parts, the glue and fasteners could likely be eliminated, allowing for easier assembly and future maintenance of the product.

Design for Environment (DFE)

Design for the environment refers to the concept of considering the effect that a product will have on the environment. The entire life cycle of the product should be considered. This includes the manufacturing of the product, the transportation of the product, the use of the product, and end of life.

Economic Input-Output Life Cycle Assessment (EIO-LCA)

One way to assess the effects that a product has on the environment is a process called EIO-LCA. This analysis takes into consideration each sector of the economy affected by manufacturing and distributing the product of interest. The economic activity, energy usage, and greenhouse gas emissions related to manufacturing and distribution of the product for each sector is calculated by the EIO-LCA software.

For the bilge pump, the sector of "Plastics pipe, fittings, and profile shapes" was used to analyze the environmental effects of the product. The current retail price of a bilge pump is $18.00, which corresponds to a retail price of $13.90 in 1997 (which is the year for which the data on the EIO-LCA software is valid). This price can be used to adjust values for $1 million of production to show the effect that producing one bilge pump has on the environment. For $1 million worth of the product, the total economic activity for all sectors is $2.28 million and for the top five sectors is $1.315 million. This corresponds to $31.69 and $18.28 of economic activity from all sectors and the top five sectors respectively per each bilge pump. The total energy required to manufacture $1 million worth of bilge pumps is 11.6 TJ for all sectors, and 6.959 TJ for the top five sectors. This result corresponds to 161.2 kJ for all sectors and 96.7 kJ for the top five sectors for one bilge pump. The global warming potential for manufacturing and distributing the product is 884 MTCO2E for all sectors and 528.3 MTCO2E for the top five sectors. These values correspond to 12.3 kTCO2E produced while manufacturing and distributing one bilge pump from all sectors or 7.34 kTCO2E produced from the top five sectors.

The following table shows the data obtained on economic activity using the 1997 purchaser price model in the EIO-LCA software for $1 million worth of "Plastics pipe, fittings, and profile shapes" produced.

Sector Total Economic Activity
(in millions of $)
Value Added
(in millions of $)
Direct Economic
(in millions of $)
Direct Economic
Plastics pipe, fittings, and profile shapes .644 .197 .642 99.7
Wholesale trade .274 .183 .232 84.7
Plastics material and resin manufacturing .197 .045 .174 88.4
Retail trade .116 .07 .112 96.8
Other basic organic chemical manufacturing .084 .018 .028 33.7
Total for top 5 sectors 1.315 .513 1.188 90.3
Total for all sectors 2.28 .99 1.59 69.7

The following table shows the data obtained on energy usage using the 1997 purchaser price model in the EIO-LCA software for $1 million worth of "Plastics pipe, fittings, and profile shapes" produced.

Sector Total Energy Used
Natural Gas
Mot Gas
Jet Fuel
Power generation and supply 3.24 0 2.57 .574 0 0 0 0 0 .098
Plastics material and resin manufacturing 1.45 .079 .093 1.17 .068 .017 .005 0 0 .009
Plastics pipe, fittings, and profile shapes 1.02 .25 0 .395 .073 .158 .11 0 0 0
Truck transportation .674 .002 0 .014 .002 .098 .558 0 0 0
Other basic organic chemical manufacturing .575 .036 .091 .408 .025 .005 .001 0 0 .005
Total for top 5 sectors 6.959 .367 2.754 2.561 .168 .278 .674 0 0 .112
Total for all sectors 11.6 .63 2.96 5.12 .57 .501 1.22 0 .242 .246

The following table shows the data obtained on greenhouse gas emissions using the 1997 purchaser price model in the EIO-LCA software for $1 million worth of "Plastics pipe, fittings, and profile shapes" produced.

Sector GWP
Power generation and supply 273 270 0 0 3.28
Truck transportation 94 92.6 .144 1.29 0
Plastics material and resin manufacturing 73.1 73.1 0 0 0
Other basic organic chemical manufacturing 46.6 32.1 0 14.6 0
Plastics pipe, fittings, and profile shapes 41.6 41.6 0 0 0
Total for top 5 sectors 528.3 509.4 .144 15.89 3.28
Total for all sectors 884 759 79.7 29.3 16

Since there is no energy or waste produced by the product itself during use, this stage in the life cycle has a negligible environmental effects. At the end of life, the product can be recycled since it made essentially of only plastic. While energy is used in recycling the product, the beneficial aspects of recycling outweigh this effect. Thus, manufacturing and distribution of the product has the largest impact on the environment. However, the processes and products use already minimize this effect during manufacturing, so there are not likely any significant environmental concerns left to be addressed in future design work.

Quantitative Analyses

Fluid Mechanics Calculations

To pass through the bilge pump, the fluid will:
1. Flow into pump entrance
2. Diverge into pump body
3. Move up pump body
4. Go through 90 degree elbow and contraction to pass through pump exit nozzle

In order for the fluid to pass through this system, the pump must provide a certain amount of head, since each of the above steps in the fluid flow is accompanied by a head loss. Most of the head loss in this system comes from what is called minor head losses associated with expansions and contractions in the flow path. The below equations represent the two ways of calculating minor head loss when the mean velocity of the flow is known. Since the velocity of fluid passing through the system may vary depending on the user, the actual head loss of the system cannot be calculated explicitly.

In the first equation, K is the head loss coefficient. In the second equation, f is the friction factor (which varies with velocity of the flow), the quantity Le is the equivalent length of an elbow, and the quantity D is the inner diameter of the pipe. The relevant values for the aquarium pump system are shown in the image to the right.

Based on timed observations, a volumetric flow rate of three gallons per minute was approximated as the speed at which water moves through the system due to gravitational effects. Using this value, the head required to move water through the system is found to be 2.718 feet, as is shown in the image below. This means that 2.718 feet of height difference is required from the entrance to the exit of the system to move water through gravity alone, or an equivalent amount of pressure must be added to the system by the pump.

A certain force is required to operate the pump. Forces are required to pull the handle up, pushing water out of the exit nozzle and drawing new water into the pump cavity, and to push the handle back down again. However, a greater force is needed to pull the handle up. The force required to pull up the handle of the pump is a combination of the weight of the water being moved, the friction between the rubber seal and the plastic wall of the pump cavity, and the drag force acting on the plunger.

The friction force acting on the seal as the pump handle is being pulled upwards can be estimated by approximating a maximum normal force as shown below. This estimation yields a friction force of 2.4 lb, which dominates over the force exerted by the weight of the water. However, this force is not so much greater that the weight of the water can be neglected. It should also be noted that the frictional force is significant enough to be felt when operating the pump even when there is no water inside to be lifted.

As the handle in the pump is pushed down, a drag force must be overcome in order to move the plunger through the water. The effect of the drag force can be seen in the image below. As the calculations demonstrate, this force is minor in comparison to the forces required to pull the handle up, as it is estimated to be 0.251 lb.

Note that the area in the equation is the area of the plunger moving through the water, the velocity is the velocity of the plunger, and the drag coefficient (Cd) was found to be 1.28 for a flat plate perpendicular to the fluid flow.

Since the maximum total force that needs to be overcome to use the pump is relatively small (3.881 lb), it can be safely assumed that the pump is operable by most people.

Stress Analysis Calculations

Another concern with the use of the bilge pump is the amount of force required to break the shaft connecting the handle and rubber seal of the pump. In the worst case scenario, a force may be applied incorrectly to the handle, and the body of the shaft will act as a moment arm, assuming that the bottom of the shaft is fixed by the pump body. The image to the right illustrates this case. In order to calculate the force required for the shaft to fail, a yield strength was assumed. The shaft was assumed to be made of PVC based on the known characteristics of this and other types of plastic. A common yield strength of PVC was found to be 6.38 ksi based on internet research.

In the equation to the left, M is the moment applied to the shaft, c is a characteristic dimension between the point of force application and the axis of rotation, and I is the moment of inertia of the shaft.

The first mode of failure analyzed is when a force is applied vertically to the handle but is isolated to the side of the handle so that half of the handle distance (w) is the characteristic dimension.

It is not probable that a user would apply this large of a force to the pump handle, so this mode of failure is relatively unlikely.

The second mode of failure analyzed is when a force is applied horizontally to the top of the handle so that the handle length and shaft length combined (L) is the characteristic dimension.

While it is unlikely for the pump to be subjected to the idealized conditions that would allow it to yield through the second failure mode, the force required to break the shaft in this mode is not unreasonable. For example, if the pump were lying around with the handle fully extended and someone pushed on the edge of the handle, enough force could potentially be applied to break the shaft. Thus, this mode of failure is much more likely than the first.

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