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