Home-made Hydraulic Ram Pump
|Pump Plans||Assembly Notes||Performance||Links|
|How It Works||Operation||Test Installation||Common Problems|
This information is provided as a service to those wanting to build their own hydraulic ram pump. The data from our experiences with one of these home-made hydraulic ram pumps is listed in Table 4 near the bottom of this document. The typical cost of fittings for an 1-1/4" pump is currently $120.00 (U.S.A.) regardless of whether galvanized or PVC fittings are used.
Click here to see a picture of an assembled ram pump
Table 1. Image Key
|1||1-1/4" valve||10||1/4" pipe cock|
|2||1-1/4" tee||11||100 psi gauge|
|3||1-1/4" union||12||1-1/4" x 6" nipple|
|4||1-1/4" brass swing check valve (picture)||13||4" x 1-1/4" bushing|
|5||1-1/4" spring check valve||14||4" coupling|
|6||3/4" tee||15||4" x 24" PR160 PVC pipe|
|7||3/4" valve||16||4" PVC glue cap|
|8||3/4" union||17||3/4" x 1/4" bushing|
|9||1-1/4" x 3/4" bushing|
All connectors between the fittings are threaded pipe nipples - usually 2" in length or shorter. This pump can be made from PVC fittings or galvanized steel. In either case, it is recommended that the 4" diameter fittings be PVC fittings to conserve weight.
Conversion Note: 1" (1 inch) = 2.54 cm; 1 PSI (pound/square inch) = 6.895 KPa or 0.06895 bar; 1 gallon per minute = 3.78 liter per minute. PR160 PVC pipe is PVC pipe rated at 160 psi pressure.
Click here to see an image-by-image explanation of how a hydraulic ram pump works
Click here to see a short
mpeg movie of an operating ram pump
(Note - this is a 6.2 mb movie clip. On slower systems (11 mbps, etc.), it will load "piece-meal" the first time. Allow it to finish playing in this fashion, then press the play button again to see it in full motion with no "buffering" stops. Dial-up users may have to download the file to see it - simply right-click on the link, then select "Save Target As..." to save it to your computer. Downloading may take considerable time if you are on a slower dial-up system.)
Pressure Chamber - A bicycle or "scooter tire" inner tube is placed inside the pressure chamber (part 15) as an "air bladder" to prevent water-logging or air-logging. Inflate the tube until it is "spongy" when squeezed, then insert it in the chamber. It should not be inflated very tightly, but have some "give" to it. Note that water will absorb air over time, so the inner tube is used to help prevent much of this absorbtion. You may find it necessary, however, to drain the ram pump occasionally to allow more air into the chamber. (The University of Warwick design (link below, pages 12-13) suggests the use of a "snifter" to allow air to be re-introduced to the ram during operation. Their design, however, is substantially different from the one offered here and provides a location (the branch of a tee) where the addition of a snifter is logical. This design does not. Also, correctly sizing the snifter valve (or hole as the case may be) can be problematical and may allow the addition of too much air, resulting in air in the drive pipe and ceasing of pumping operation. For these reasons we have elected not to include one in this design.)
According to information provided by the University of Warwick (UK) ( http://www.eng.warwick.ac.uk/dtu/pubs/tr/lift/rptr12/tr12.pdf , page 14), the pressure chamber should have a minimum volume of 20 times the expected delivery flow per "cycle" of the pump, with 50 times the expected delivery being a better selection. The chart below provides some recommended minimum pressure chamber sizes based on 50 times the expected delivery flow per "cycle." Note that larger pressure chambers will have not have any negative impact on the pump performance (other than perhaps requiring a little more time to initially start the pump). Some of the lengths indicated are quite excessive, so you may prefer to use two or three pipes connected together in parallel to provide the required pressure chamber volume. Well pump pressure tanks will also work well - just make sure they have at least the minimum volume required.
Table 2. Suggested Minimum Pressure Chamber Sizes
(Based on ram pumps operating at 60 cycles per minute.)
Length of Pipe Required for Pressure Chamber
(for indicated pipe diameter)
(lengths are in inches)
2 inch 2-1/2 inch 3 inch 4 inch 6 inch 8 inch 10 inch 12 inch 3/4 0.0042 0.21 15 11 7 -- -- -- -- -- 1 0.0125 0.63 45 32 21 -- -- -- -- -- 1-1/4 0.020 1.0 72 51 33 19 -- -- -- -- 1-1/2 0.030 1.5 105 74 48 27 -- -- -- -- 2 0.067 3.4 -- 170 110 62 27 16 -- -- 2-1/2 0.09 4.5 -- 230 148 85 37 22 14 -- 3 0.15 7.5 -- -- 245 140 61 36 23 16 4 0.30 15 -- -- -- 280 122 72 45 32 6 0.80 40 -- -- -- -- 325 190 122 85 8 1.60 80 -- -- -- -- -- 380 242 170
(Note - it is quite difficult to push a partially-inflated 16 inch bicycle inner tube into a 3 inch PVC pipe. Due to this we suggest the pressure chamber be a minimum of 3 inches in diameter.)
A 4" threaded plug and 4" female adapter were originally used instead of the 4" glue-on cap shown in the image, This combination leaked regardless of how tightly it was tightened or how much teflon tape sealant was used, resulting in water-logging of the pressure chamber. This in turn dramatically increased the shock waves and could possibly have shortened pump life. If the bicycle tube should need to be serviced when using the glue cap design, the pipe may be cut in half then re-glued together using a coupling.
Valve Operation Descriptions - Valve #1 is the drive water inlet for the pump. Union #8 is the exit point for the pressurized water. Swing check valve #4 is also known as the "impetus" or "waste" valve - the extra drive water exits here during operation. The "impetus" valve is the valve that is operated manually at the beginning (by pushing it in with a finger) to charge the ram and start normal operation.
Valves #1 and #7 could be ball valves instead of gate valves. Ball valves may withstand the shock waves of the pump better over a long period of time.
The swing check valve (part 4 - also known as the impetus valve) can be adjusted to vary the length of stroke (please note that maximum flow and pressure head will be achieved with this valve positioned vertically, with the opening facing up). Turn the valve on the threads until the pin in the clapper hinge of the valve is in line with the pipe (instead of perpendicular to it). Then move the tee the valve is attached to slightly away from vertical, making sure the clapper hinge in the swing check is toward the top of the valve as you do this. The larger the angle from vertical, the shorter the stroke period (and the less potential pressure, since the water will not reach as high a velocity before shutting the valve). For maximum flow and pressure valve #4 should be in a vertical position (the outlet pointed straight up).
Swing check valve #4 should always be brass (or some metal) and not plastic. Experiences with plastic or PVC swing check valves have shown that the "flapper" or "clapper" in these valves is very light weight and therefore closes much earlier than the "flapper" of a comparable brass swing check. This in turn would mean lower flow rates and lower pressure heads.
The pipe cock (part 10) is in place to protect the gauge after the pump is started. It is turned off after the pump has been started and is operating normally. Turn it on if needed to check the outlet pressure, then turn it back off to protect the gauge.
Drive Pipe - The length of the drive pipe (from water source to pump) also affects the stroke period. A longer drive pipe provides a longer stroke period. There are maximum and minimum lengths for the drive pipe (see the paragraph below Table 2). The drive pipe is best made from galvanized steel (more rigid is better) but schedule 40 PVC can be used with good results. The more rigid galvanized pipe will result in a higher pumping efficiency and allow higher pumping heights. Rigidity of the drive pipe seems to be more important in this efficiency than straightness of the drive pipe.
Drive pipe length and size ratios are apparently based on empirical data. Information from University of Georgia publications (see footnote) provides an equation from Calvert (1958), which describes the output and stability of ram pump installations based on the ratio of the drive pipe length (L) to the drive pipe diameter (D). The best range is an L/D ratio of between 150 and 1000 (L/D = 150 to L/D = 1000). Equations to use to determine these lengths are:
Minimum inlet pipe length: L = 150 x (inlet pipe size)
Maximum inlet pipe length: L = 1000 x (inlet pipe size)
If the inlet pipe size is in inches, then the length (L) will also be presented in inches. If inlet pipe size is in mm, then L will be presented in mm.
Drive Pipe Length Example: If the drive pipe is 1-1/4 inches (1.25 inches) in diameter, then the minimum length should be L = 150 x 1.25 = 187.5 inches (or about 15.6 feet). The maximum length for the same 1-1/4 inch drive pipe would be L = 1000 x 1.25 = 1250 inches (104 feet). The drive pipe should be as rigid and as straight as possible.
Stand pipe or no stand pipe? Many hydraulic ram installations show a "stand pipe" installed on the inlet pipe. The purpose of this pipe is to allow the water hammer shock wave to dissipate at a given point. Stand pipes are only necessary if the inlet pipe will be longer than the recommended maximum length (for instance, in the previous example a stand pipe may be required if the inlet pipe were to be 150 feet in length, but the maximum inlet length was determined to be only 104 feet). The stand pipe - if needed - is generally placed in the line the same distance from the ram as the recommended maximum length indicated.
The stand pipe must be vertical and extend vertically at least 1 foot (0.3 meter) higher than the elevation of the water source - no water should exit the pipe during operation (or perhaps only a few drops during each shock wave cycle at most). Many recommendations suggest that the stand pipe should be 3 sizes larger than the inlet pipe. The supply pipe (between the stand pipe and the water source) should be 1 size larger than the inlet pipe.
The reason behind this is simple - if the inlet pipe is too long, the water hammer shock wave will travel farther, slowing down the pumping pulses of the ram. Also, in many instances there may actually be interference with the operation of the pump due to the length of travel of the shock wave. The stand pipe simply allows an outlet to the atmosphere to allow the shock wave to release or dissipate. Remember, the stand pipe is not necessary unless the inlet pipe will have to be longer than the recommended maximum length.
Another option would be to pipe the water to an open tank (with the top of the tank at least 1 foot (0.3 meter) higher than the vertical elevation of the water source), then attach the inlet pipe to the tank. The tank will act as a dissipation chamber for the water hammer shock wave just as the stand pipe would. This option may not be viable if the tank placement would require some sort of tower, but if the topography allows this may be a more attractive option.
Click here to view sketches of these types of hydraulic ram pump installations
(loads in 70 seconds over 28.8 modem)
The pump will require some back pressure to begin working. A back pressure of 10 psi or more should be sufficient. If this is not provided by elevation-induced back pressure from pumping the water uphill to the delivery point (water trough, etc.), use the 3/4" valve (part 7) to throttle the flow somewhat to provide this backpressure.
As an alternative to throttling valve part 7 you may consider running the outlet pipe into the air in a loop, and then back down to the trough to provide the necessary back pressure. A total of 23 feet of vertical elevation above the pump outlet should be sufficient to provide the necessary back pressure. This may not be practical in all cases, but adding 8 feet of pipe after piping up a hill of 15 feet in elevation should not be a major problem. This will allow you to open valve #7 completely, preventing stoppage of flow by trash or sediment blocking the partially-closed valve. It is a good idea to include a tee at the outlet of the pump with a ball valve to allow periodic "flushing" of the sediment just in case.
The pump will have to be manually started several times when first placed in operation to remove the air from the ram pump piping. Start the pump by opening valve 1 and leaving valve 7 closed. Then, when the swing check (#4) shuts, manually push it open again. (The pump will start with valve 7 closed completely, pumping up to some maximum pressure before stopping operation.) After the pump begins operation, slowly open valve 7, but do not allow the discharge pressure (shown on gauge #11) to drop below 10 psi. You may have to push valve #4 open repeatedly to re-start the pump in the first few minutes (10 to 20 times is not abnormal) - air in the system will stop operation until it is purged.
The unions, gate (or ball) valves, and pressure gauge assembly are not absolutely required to make the pump run, but they sure do help in installing, removing, and starting the pump as well as regulating the flow.
Some information suggests that typical ram pumps discharge approximately 7 gallons of water through the waste valve for every gallon pressurized and pumped. The percentage of the drive water delivered actually varies based on the ram construction, vertical fall to pump, and elevation to the water outlet. The percentage of the drive water pumped to the desired point may be approximately 22% when the vertical fall from the water source to the pump is half of the elevation lift from the ram to the water outlet. It may be as low as 2% or less when the vertical fall from the water source to the pump is 4% of the elevation lift from the ram to the water outlet. Rife Hydraulic Engine Manufacturing Company literature (http://www.riferam.com/) offers the following equation:
0.6 x Q x F/E = D
Q is the available drive flow in gallons per minute, F is the fall in feet from the water source to the ram, E is the elevation from the ram to the water outlet, and D is the flow rate of the delivery water in gallons per minute. 0.6 is an efficiency factor and will differ somewhat between various ram pumps. For instance, if 12 gallons per minute is available to operate a ram pump (D), the pump is placed 6 feet below the water source (F), and the water will be pumped up an elevation of 20 feet to the outlet point (E), the amount of water that may be pumped with an appropriately-sized ram pump is
0.6 x 12 gpm x 6 ft / 20 ft = 2.16 gpm
The same pump with the same drive flow will provide less flow if the water is to be pumped up a higher elevation. For instance, using the data in the previous example but increasing the elevation lift to 40 feet (E):
0.6 x 12 gpm x 6 ft / 40 ft = 1.08 gpm
Table 3. Typical Hydraulic Ram specifications (Expected water output will be approximately 1/8 of the input flow, but will vary with installation fall (F) and elevation lift (E) as noted above. This chart is based on 5 feet of lift (E) per 1 foot of fall (F).)
|At Minimum Inflow||At Maximum Inflow|
(gallons per minute)
(gallons per minute)
(gallons per minute)
(gallons per minute)
Table 4. Test Installation Information
|Drive Pipe Size||1-1/4 inch Schedule 40 PVC|
|Outlet Pipe Size||3/4 inch Schedule 40 PVC|
|Pressure Chamber size||4 inch PR160 PVC|
|Pressure Chamber Length||36 inches|
|Inlet Pipe Length||100 feet|
|Outlet Pipe Length||40 feet|
|Drive Water (Inlet) elevation above pump||4 feet|
|Elevation from pump outlet to delivery outlet||12 feet|
Click here to see pictures of the test installation (loads in 38 seconds over 28.8 modem)
Table 5. Trial 1 Performance Data
|At Installation (5/17/99)||After Installation
(with water-log) (5/21/99)
|After Clearing Water-log (6/20/99)|
|Shutoff Head||5 to 17 psi||22 psi||50 psi||22 psi|
|Operating Head||10 psi||10 psi||10 psi||10 psi|
|Operating Flow Rate||0.50 to 1.00 gpm||0.28 gpm||1.50 gpm||0.33 gpm|
Note that we used a 4" threaded plug and a 4" female adapter for our test pump (instead of the recommended 4" glue cap (#16) shown in the figure). Two days after installation the pump air chamber was effectively water-logged due to leakage past the threads of these two fittings, which was shown by the pronounced impulse pumping at the outlet discharge point. If the pump were allowed to remain waterlogged, it would shortly cease to operate - and may introduce damage to the pipe or other components due to pronounced water hammer pressure surges.
The large range of expected values for shutoff head is due to the unknown efficiency of the pump. Typical efficiencies for ram pumps range from 3 feet to 10 feet of lift for every 1 foot of elevation drop from the water inlet to the pump.
The most common problems that prevent a ram pump from operating:
(1) The swing check valve (valve #4) must be the same size as the drive pipe and the tee (tee #2) it is attached to.
(2) The drive pipe is too long or too short. For a 1.25 inch (3.2 cm) drive pipe that means no shorter than 15.6 feet (4.8 meters), and no longer than 104 feet (31.8 meters). Too short of a drive pipe may not allow the pressure wave to develop; too long of a pipe will allow successive pressure waves to interfere with one another. Use the equation provided above to find appropriate lengths for other pipe sizes.
(3) A garden hose is supplying the test installation. The flow velocity from the hose into the drive pipe will create pressure on the waste valve. The best test setup is to plumb the drive pipe into a bucket or a livestock water tank, and keep that filled with water. Sticking a hose into the drive pipe destroys the water hammer wave.
(4) The air has not been purged from the system. Usually the waste valve flapper (valve #4) must be manually pushed from 20 to 50 times to get the pump started. 100 times, though, is too much – something’s wrong.
(5) The valve on the discharge side is open (valve #7). This valve should be closed while the pump is being started – the pump will run 30+ seconds with it closed after it starts, building pressure. After the pump starts running, slowly open that valve. Make sure, though, that at least 10 psi (0.7 bar or 69 kPa) of back pressure is maintained on the pump. It will not work with less.
(6) There is not enough elevation drop from the drive pipe inlet to the ram pump. 5 feet (1.5 m) of elevation drop is recommended. The pump may work with only 4 feet (1.2 m) of elevation drop. It will not work well or at all with less. (Note that if the pipe is plumbed into a pool of water, the elevation difference is taken from the surface of the water to the ram pump, not from the location of the drive pipe inlet.)
(7) There is an air leak in the pressure chamber. Larger PVC pipe sizes ( 2 inches or 5 cm and larger) require the use of a PVC primer to soften and clean the PVC before the PVC cement is used. Failure to use the primer may prevent the joint from joining properly and allow air to escape or the joint to come apart. Primer is usually not needed on 1.5 inch (3.8 cm) and smaller pipes.
Hydraulic Ram Web Sites
CAT Hydraulic Ram Tipsheet
Green and Carter
NC State's EBAE 161-92, "Hydraulic Ram Pumps"
Schott Solar Electric
University of Warwick (UK) Ram Pump Publications
Some information for this web page - and the initial information concerning construction of a home-made hydraulic ram pump - was provided by University of Georgia Extension publications #ENG98-002 and #ENG98-003 (both Acrobat "pdf" files) by Frank Henning. Publication #ENG98-002 also describes the pumping volume equations for hydraulic ram pumps.
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This page created and maintained by Bryan Smith,
Clemson University Cooperative Extension, Laurens County.
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