konandrew 's List: Fluid Mechanics

Home-made Hydraulic Ram Pump

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

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.)

Assembly Notes:

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.