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How a Hydraulic Ram Pump works

The concept behind the ram idea is a "water hammer" shock wave.  Water has weight, so a volume of water moving at a certain speed has momentum - it doesn't want to stop immediately.  If a car runs into a brick wall the result is crumpled metal.  If a moving water flow in a pipe encounters a suddenly closed valve, a pressure "spike" or increase suddenly appears due to all the water being stopped abruptly (that's what water hammer is - the pressure spike).  If you turn a valve off in your house quickly, you may hear a small "thump" in the pipes.  That's water hammer.

Here's a simplified version (see note 1) of how the hydraulic ram pump actually works, step-by-step:

(1) Water (blue arrows) starts flowing through the drive pipe and out of the "waste" valve (#4 on the diagram), which is open initially.  Water flows faster and faster through the pipe and out of the valve. (Click here to see an actual image of an operating ram pump for this step.) 


(2) At some point, water is moving so quickly through the brass swing check "waste" valve (#4) that it grabs the swing check's flapper, pulling it up and slamming it shut.  The water in the pipe is moving quickly and doesn't want to stop.  All that water weight and momentum is stopped, though, by the valve slamming shut.  That makes a high pressure spike (red arrows) at the closed valve.  The high pressure spike forces some water (blue arrows) through the spring check valve (#5 on the diagram) and into the pressure chamber.  This increases the pressure in that chamber slightly.  The pressure "spike" the pipe has nowhere else to go, so it begins moving away from the waste valve and back up the pipe (red arrows).  It actually generates a very small velocity *backward* in the pipe. (Click here to see an actual image of an operating ram pump for this step.  Note the drops of water still falling to the ground in the image.)

(3) As the pressure wave or spike (red arrows) moves back up the pipe, it creates a lower pressure situation (green arrows) at the waste valve.  The spring-loaded check valve (#5) closes as the pressure drops, retaining the pressure in the pressure chamber. (see note 1)

(4) At some point this pressure (green arrows) becomes low enough that the flapper in the waste valve (#4) falls back down, opening the waste valve again.  (Click here to see an actual image of a ram pump for this step.)

(5) Most of the water hammer high pressure shock wave (red arrows) will release at the drive pipe inlet, which is open to the source water body.  Some small portion may travel back down the drive pipe, but in any case after the shock wave has released, pressure begins to build again at the waste valve (#4) simply due to the elevation of the source water above the ram, and water begins to flow toward the hydraulic ram again.

(6) Water begins to flow out of the waste valve (#4), and the process starts over once again.

Steps 1 through 6 describe in layman's terms a complete cycle of a hydraulic ram pump.  Pressure wave theory will explain the technical details of why a hydraulic ram pump works,  but we only need to know it works.  (One American company has been manufacturing and selling hydraulic rams since the 1880ís).  The ram pump will usually go through this cycle about once a second, perhaps somewhat more quickly or more slowly depending on the installation. 

Each "pulse" or cycle pushes a little more pressure into the pressure chamber.  If the outlet valve is left shut, the ram will build up to some maximum pressure (called shutoff head on pumps) and stop working.

Note 1: In actuality the functioning ram pump involves three different pressure waves: (a) the initial high pressure spike when the waste valve flapper closes, which travels back up the drive pipe to the water source; (b) a "normal" pressure wave, which then travels back down the drive pipe from the water source to the closed waste valve; and (c) a low pressure wave, which then travels back up the drive pipe to the water source. It is at this point that the waste valve flapper opens. Note that these pressure waves travel at the speed of sound (depending on the drive pipe material), so all this happens quite quickly. This complex procedure was not included in the steps above for the sake of simplicity in giving a layman's understanding of the process.
(References: Fluid Mechanics, Second edition, Roberson and Crowe, and personal communications with Mr. John Stanley, 2013.)

Note 2: The ram is quite inefficient.  Usually 8 gallons of water must pass through the waste valve for each 1 gallon of water pumped by the ram.  That is acceptable for a creek or river situation, but may not be a good option for a pond that does not have a good spring flow. 

(Page and images copyright 2007 Bryan Smith.  All rights reserved.)

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