What is a Hydraulic Ram Pump?- A Complete Guide

What is Hydraulic Ram Pump?

A hydraulic ram, or hydram, is a cyclical water pump powered by hydropower. It takes in water with a “hydraulic head” (pressure) and a flow rate and outputs water with a higher hydraulic head and a lower flow rate.

The device uses the water hammer effect to develop a pressure that allows some of the incoming water that powers the pump to be raised to a higher point than the water originally started.

The hydraulic ram is sometimes used in remote areas where there is both a source of low head hydropower and the need to pump water to a destination higher than the source. In this situation, the ram is often useful, as it does not need any external source of energy other than the kinetic energy of flowing water.

Hydraulic Ram Pump Operation

Hydraulic ram pumps operate by utilizing pressure developed by a “water hammer” shock wave. Any object in motion has an inertial force. Energy is required to place the object in motion, and energy will also be required to stop the motion, with more energy being required if the motion is started or stopped quickly.

A flow of water in a pipe also has inertia (or momentum) that resists sudden changes in velocity. Slowly closing a valve allows this inertia to dissipate over time, producing very little pressure increase in the pipe.


Closing a valve very rapidly will create a pressure surge or shock wave as the flowing water stops, which moves back up the pipe – much like a train stop, with individual train cars hitting the coupling in front of them in rapid succession as the brakes are applied.

The more quickly the valve is closed, the larger the shock wave produced. A faster water flow will also produce a larger shock wave when a valve is closed since more inertia or momentum is involved. A longer pipe will also produce a larger shock wave for the same reason.

A hydraulic ram relies on a non-pressurized flow of water in a pipe placed from the water source to the pump (called a “drive” pipe). This flow is produced by placing the hydraulic ram some distance below a water source and running the drive pipe from the water source to the pump. The hydraulic ram employs two check valves, which are the only moving parts in the pump.


Step-by-step explaining how a hydraulic ram pump operates:

  • 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 waste valve.
  • Step 2: At some point water is moving so quickly through the waste valve (#4) that it pushes the valve’s flapper up and slams it shut. The water in the pipe was moving quickly and had considerable momentum, but all the water weight and momentum is stopped by the valve’s closure. That creates a high-pressure spike (red arrows) at the closed waste valve. The high-pressure spike forces some water (blue arrows) through the check valve (#5 on the diagram) and into the pressure chamber. This increases the pressure in that chamber slightly. The pressure “spike” in the pipe also begins moving away from the waste valve and up the drive pipe (red arrows) at the speed of sound and is released at the drive pipe inlet.
  • Step 3: After the high-pressure wave reaches the drive pipe inlet, a “normal” pressure wave (green arrows) travels back down the pipe to the waste valve. The check valve (#5) may still be open slightly depending on backpressure, allowing water to enter the pressure chamber.
  • Step 4: as soon as the normal pressure wave reaches the waste valve, a low-pressure wave (brown arrows) travels up the drive pipe, which lowers the pressure at the valves and allows the waste valve to open and the check valve (#5) to close.
  • Step 5: When the low-pressure wave reaches the drive pipe inlet, a normal pressure wave travels down the drive pipe to the valves. Normal water flow due to the elevation of the source water above the ram follows this pressure wave, and the next cycle begins.

Efficiency of Hydraulic Ram Pump

Typical energy efficiency is 60%, but up to 80% is possible. This should not be confused with the volumetric efficiency, which relates the volume of water delivered to total water taken from the source. The portion of water available at the delivery pipe will be reduced by the ratio of the delivery head to the supply head.

Thus, if the source is 2 meters above the ram and the water is lifted to 10 meters above the ram, only 20% of the supplied water can be available, the other 80% being spilled via the waste valve. These ratios assume 100% energy efficiency.

Actual water delivered will be further reduced by the energy efficiency factor. In the above example, if the energy efficiency is 70%, the water delivered will be 70% of 20%, i.e., 14%.

Assuming a 2-to-1 supply-head-to-delivery-head ratio and 70% efficiency, the delivered water would be 70% of 50%, i.e., 35%. Very high ratios of delivery to supply head usually result in lowered energy efficiency. Suppliers of rams often provide tables giving expected volume ratios based on actual tests.

Starting Operation

A ram newly placed into operation or which has stopped cycling should start automatically if the waste valve weight or spring pressure is adjusted correctly, but it can be restarted as follows:

  • If the waste valve is in the raised (closed) position, it must be pushed down manually into the open position and released.
  • If the flow is sufficient, it will then cycle at least once.
  • If it does not continue to cycle, it must be pushed down repeatedly until it cycles continuously on its own, usually after three or four manual cycles.
  • If the ram stops with the waste valve in the down (open) position it must be lifted manually and kept up for as long as necessary for the supply pipe to fill with water and for any air bubbles to travel up the pipe to the source.

This may take some time, depending on supply pipe length and diameter. Then it can be started manually by pushing it down a few times as described above. Having a valve on the delivery pipe at the ram makes starting easier.

Closing the valve until the ram starts cycling, then gradually opening it to fill the delivery pipe. If opened too quickly it will stop the cycle. Once the delivery pipe is full the valve can be left open.

Common operational problems

Failure to deliver sufficient water may be due to improper adjustment of the waste valve, having too little air in the pressure vessel, or simply attempting to raise the water higher than the level of which the ram is capable.

The ram may be damaged by freezing in winter, or loss of air in the pressure vessel leading to excess stress on the ramparts. These failures will require welding or other repair methods and perhaps parts replacement.

It is not uncommon for an operating ram to require occasional restarts. The cycling may stop due to poor adjustment of the waste valve, or insufficient water flow at the source. Air can enter if the supply water level is not at least a few inches above the input end of the supply pipe.

Other problems are blockage of the valves with debris, or improper installation, such as using a supply pipe of non-uniform diameter or material, having sharp bends or a rough interior, or one that is too long or short for the drop, or is made of an insufficiently rigid material. A PVC supply pipe will work in some installations but a steel pipe is better.