All ram pumps work on the principle of momentum, which is controlled by a cycle set up by the interaction of two valves—an impetus valve and a flapper valve— in the pump.
- When the impetus (aka “waste”) valve is opened (this must initially be done by hand to start the pump cycling), water begins to flow down the drive pipe and through the impetus valve as in Figure 1.
- The drive water velocity increases until water friction slams the impetus valve shut, as in Figure 2. The momentum of the water forces open the flapper valve and pushes water past it to pressurize the air chamber above the water level.
- In Figure 3, the water pressure above the flapper valve overcomes the spent momentum below it, forcing the flapper closed again. The water that made it past the flapper in Figure 2 is then forced by the extra air pressure out the delivery pipe and up to the delivery point.
- Since the momentum of the water coming down the drive pipe was spent, the pressure in the impetus area momentarily decreases to zero, the impetus valve falls open, allowing water to flow down the drive pipe again as in Figure 4 (just like Figure 1), starting the cycle over again.
This process occurs over and over until something happens to stop the cycle. Ram pumps can cycle anywhere from 25 to 300 times per minute. The frequency of the cycle is adjustable by changing the length of the stroke of the impetus valve. A longer stroke produces a lower frequency. Weight added to or subtracted from an impetus valve, and even springs, have been used to adjust the frequency. Lower frequency means more of the supply flows to and through the pump and more is pumped up the delivery pipe.
The stroke is adjusted to restrict the amount of water used to the amount available from the source, or if the supply is unlimited, to regulate the amount delivered to match the amount needed.