skip to Main Content

How Does A Ram Pump Work?

Ram Pump

*We may earn a commission for purchases made using our links.  Please see our disclaimer to learn more.

The basic principle of a ram pump is to cause a large amount of water to fall a short distance which in turn pumps a small amount of water to a higher elevation. They are not super-efficient – usually only 2% to 20% of the water flowing through a ram pump will actually be delivered to the storage tank and the rest will flow back into the source of the water but the secret of their success lies in not requiring any energy input apart from the flow of a stream and in steadily accumulating tiny spurts of water to add up to a full-on water-supply way above the level of the pump.

Ram pumps have been around since the late 1700s. The first self-acting ram pump was invented by the Frenchman Joseph Michel Montgolfier (best known as a co-inventor of the hot air balloon) in 1796 for raising water in his paper mill at Voiron, France. His friend Matthew Boulton took out a British patent on his behalf in 1797.

There are ram pumps lifting water in every part of the world, many of which have been pumping quietly and effectively for decades.

To go into a bit more detail:

ram pump

When the head of a hammer encounters a nail at speed the hammer’s velocity is converted into pressure on the nail. In the same way all pumps are converting some form of energy into pressure and velocity. A hand pump for your bicycle tire is exchanging your physical energy for pressure. An electric pump is exchanging electrical energy. A ram pump is fed a comparatively large volume of water at a low pressure and sacrifices a huge proportion of the volume in exchange for a gain in pressure.

  • Ram pumps are fed by gravity from a header tank or weir via what is known as the drive pipe. (The length and volume of this drive pipe is critical in the functioning of the pump.)
  • Inside the pump the water is discharged through a velocity-sensitive valve, called the dash valve, which is tuned by adjusting its weights and stroke length to shut off in response to a certain water flow.
  • The sudden deceleration of all the water in the drive pipe is much like the head of the hammer hitting the nail and the water’s weight and velocity is transferred to the inner walls of the pump in the form of pressure. The only escape for the pressurized water is through the delivery valve and into the accumulator or pressure vessel.
  • Following this sudden deceleration the water in the drive pipe recoils briefly, causing the dash valve to re-open and allowing the contents of the drive pipe to begin accelerating out of the dash valve again, until sufficient velocity is achieved to close the dash valve and set off a repeat of the process.

These cycles can take place between one and three times a second, depending on your exact application. The end result is an accumulation of water in the pressure tank which is at much greater pressure than the water in the drive pipe and which can then be pushed up to locations that are much higher in elevation than the original header tank or weir.

To demonstrate the age and long-lasting respectability of the ram pump idea let me introduce you to the “Hydraulic Ram” section of a fascinating old trilogy in my possession entitled The Modern Practical Plumber written by A.C. Martin and John H. Henwood and published in 1929 by Caxton Publishing Company of London, U.K.

modern plumber


The design has not really changed much in the last century so I will quote the book at length and supply their original hand-drawn diagrams (though I have printed the labels to make them more easy to read).

So, here we go, Martin and Henwood on “The Hydraulic Ram”:-

“Hydraulic rams devised to raise water by the force of flowing water can only be applied to that purpose where the contour of the country permits and where water is plentiful and suitable for the purpose of the premises supplied.  A ram pump is made of cast iron [author’s note -see YouTube video below for a PVC version] and is usually enclosed by a small brick chamber large enough for a man to get inside.  

 Where it is difficult to arrange a sufficient head to work the ram it may be sunk in the ground to obtain a greater working head, providing the tail water from the ram can get away freely to some natural outlet.   A ram designed to raise water, say, 20 feet high will not work if such height is exceeded, or vice versa.  A ram which under given conditions as to “head of water” on the ram and length of drive, etc., would work to raise water, say, to 100 feet, and would fail to work if the height was below this. 

In considering the application of a ram, careful particulars should be taken and forwarded to an expert or the manufacturers of hydraulic rams, so that one can be selected designed to meet the circumstances of the case. 

Fig. 1 shows a cross-section of the pump’s body and valves. Fig. 2 shows in  diagrammatic form the ram in position to supply a country residence.

The action of the ram is as follows:

ram pump diagram

Water flowing down the drive pipe escapes at the dash valve until sufficient speed is gathered to close this valve.  When this happens, the power generated is expended by striking on the back of the dash valve from which it recoils. At the recoil a quantity of water is squirted through the delivery valve into the air vessel from which it cannot return, owing to the closing of the seating, so by the elasticity of the air is pressed up the delivery pipe (see Fig. 2).  At the recoil of the drive water from dash valve, as explained, a vacuum is left which allows the dash valve to drop open again. The drive water recommences to flow, and, gathering speed, again closes the dash valve, and the whole operation is automatically repeated, water being discharged at each stroke into the tank provided.  

To start the ram it is usually necessary to work the dash valve by hand or foot until the delivery pipe is charged to the discharging point. The dash valve is then regulated as to length of stroke for the best result. As long a stroke as possible to which the ram will work is likely to be less erratic in result than a speedier short stroke.

Owing to the measured beat and noise of the apparatus, in Scotland and the north country, it is sometimes spoken of as a “water-hammer.”

Generally the length of drive pipe with a 50-foot minimum length should exceed the height to which the ram has to raise water.  It must have a good working “head,” – 2 feet 6 inches to 3 feet is considered a minimum.

As the delivery pipe forms a telephonic communication to the building, it is advisable to run this pipe outside, encased in a wooden box filled with sawdust or other suitable insulating material.  The pipe should not rest on the edge of the storage tank.  The air vessel should be at least equal in capacity to the contents of the delivery pipe.

The air gradually becomes absorbed in the passing water, so that it is necessary to periodically empty out and recharge to again trap a cushion of air.  Sometimes a small valve known as a “Sniffle” valve is inserted just below the delivery valve.  This has the effect of surcharging the water with air so that the air of the air vessel is not robbed by “flat” water.

Working Capabilities of Rams

ram pump 2

The efficiency of rams varies considerably according to the design and the conditions under which they are working. The efficiency varies from 20% to 70% against the theoretical duty. A convenient formula for this work is:

basic formula

The author has found that such formulae are very perplexing to the young plumbing student, and if not carefully worked have the effect of frightening him away from evening classes.  If he will get a pencil out and assume a few problems, he will find how easy they really are to work by substituting figures which the letters represent.

Q = quantity of water in gallons passing through the ram (see Fig.2)

q = quantity of water raised in gallons

H = head of water in feet on the ram.

h = height to which water is raised in feet.

Example 1

Assume that 30 gallons per minute are flowing down the drive pipe under working conditions and that the height to which the water is to be raised is 45 feet.  The head of water on the ram is 9 feet; the quantity of water raised theoretically will be:

example 1

If an efficiency of 60 % duty is taken as the actual result, 6 x .6 = 3.6 gallons discharged 45 feet above the ram and under the given conditions.

Example 2

A ram has an available fall of 10 feet.  What quantity per minute in gallons will have to flow down the drive pipe to raise 5 gallons per minute to a point 50 feet above the ram?  

example 2


This is only a theoretical amount, so allowing 60% per cent for the actual amount, and it will need more to do the work:

example 2 corrected

needed to flow down the drive pipe per minute to raise 5 gallons per minute to the required height.


The power is generated from h (which is the length of the drive pipe) being an important factor.  The blow struck in the ram will be the result of suddenly arresting a moving body of water.  The power is the velocity of the water times the weight of the flowing water in the drive pipe.  The length of the drive pipe should be from three-quarters to one and a quarter times the vertical height to which the water has to be raised.

A minimum head of 2 feet 6 inches is usually fixed for effective work.  Excessive heads should be avoided, as it results in undue wear and tear on the working parts.

Fig. 2 and Fig. 3 show, partly in cross-section, the whole outfit to raise water from a local stream, and in the second case from a lake, to a storage tank situated in the roof of a country residence.

ram pump 3

Where the water is unsuitable for general domestic purposes, as, for instance, from a stagnant pond or lake, it may be first passed through a filter bed before reaching the “heading-up tank”.

In districts where no open lake or stream exists, it is sometimes possible to gather suitable subsoil waters by means of a system of sub-irrigation pipes led to a store tank, gathering together the little driblets of water into the main conduit to be led to this tank.

Where the supply is insufficient to keep the ram constantly at work, a device may be obtained which automatically shuts off the ram as the water recedes in the collecting or “heading-up” tank, thus preventing the water from trickling to waste down the drive pipe when there is insufficient water to cause it to work properly. When the water rises to a height sufficient to work the ram again, it automatically commences pumping again.

Where water is scarce, it can sometimes be arranged for a smaller ram to work on the tail water from the large ram.

The intake of the supply pipe should be protected by a rose piece and a vertical bar screen from leaves and floating matter gaining access to the drive pipe.  A chain is attached to the hinged flap of the intake so that it can be operated from above (as shown in Fig. 3).”


In the interests of self-sufficiency – a ram pump might be an option to explore!

See video below for creating a PVC version of a Ram Pump.


Back To Top
×Close search