A Model Hydraulic Ram

(And How The Real Ones Worked)


| July/August 1990



Air pumping engine

7574 So. 74 Street Franklin, Wisconsin 53132

Hydraulic rams have been around for a long time. Basically, a hydraulic ram is an automatic pumping device which utilizes a moderate fall in a water supply to raise a fraction of the water passed through it to a greater height. It was invented by John Whitehurst of England in 1772. The following diagram and story illustrate the discovery of the principal behind using water pressure to raise water to a higher level.

In England during the 1700's, water pipes were made of lead. The following event supposedly took place in a hospital. In Figure 1, when the plug cock was turned off quickly, the pipe burst behind the cock due to the weight and momentum of the water moving in the pipe. The water in the pipe tried to compress the water behind the cock causing a pressure buildup strong enough to burst the pipe. The local plumber, realizing the problem, soldered a smaller pipe into the larger pipe at the point where the burst took place and ran the small pipe back to the supply tank to relieve the pressure (Figure 2). Now every time the cock was turned off, the water rushed up the pipe and back into the supply tank. The plumber then got the idea to raise the small pipe to the next higher floor to fill a cistern. This worked, so he finally extended the pipe to the top floor of the building and placed a cistern there. By placing an air chamber in the line with a valve at its base to prevent the water from draining back down, the hydraulic ram evolved (Figure 3).

Whitehurst's ram was not self acting, but the valve was manually opened and closed. The self acting waste valve (or beat valve) was added in 1776 by Joseph Montgolfier. In 1816, Pierre Montgolfier was awarded the British patent for a double acting ram that used dirty stream water to pump clean water from a well to a water storage tank. Pierre also added a 'snift valve' to admit air to the chamber with every stroke because water under pressure absorbs air; thus the air chamber slowly fills with water until the air is gone, causing the pipe to 'hammer'. By replenishing the air, the ram will now run continuously for many years without attention.

Rams have been made in many sizes ranging from small domestic units to large units which could pump 250,000 gallons per day into a city's reservoir or elevated water tank. Some cities used rams for their water supply. I found mention of a ram that supplied a town in Pennsylvania, and also one being used in San Luis Obispo, California. I do not know if any of the large rams still exist. If so, this author would like to see one. One company's catalog advertised a ram that would raise 400,000 gallons per day to a height of 800 feet. My fascination with rams began about 1960 when, as a 14 year old, I saw one in a junk yard that I used to frequent, along with a Rider Ericsson hot air pumping engine, neither of which did I have the sense to buy!

Now to the operation of the hydraulic ram. Water enters the ram through the drive pipe A and flows through the beat valve B until the velocity of the water rushing past causes the beat valve to close rapidly, suddenly stopping the flow of water. The weight of the water that is moving in the drive pipe presses against the water in the ram body, raising the pressure in the body. This pressure opens the delivery valve D, and the water rushes into the air chamber E until the pressure drops from the rebound of the water. The water in the ram body is actually elastic and rebounds back up the delivery pipe A. This does two things at the same time. The recoil creates a vacuum under the beat valve B causing it to open and also the drop in pressure closes the delivery valve D. Inside the dome, the water has compressed the air and after the delivery valve D closes, the compressed air forces the water up the delivery pipe F until the pressure equalizes. Now back in the ram body C, water once again flows downhill into the ram and out the beat valve B, starting the whole process again. A suction valve, or just a capillary tube, is placed either on the ram body or in the drive pipe just before entering the ram to admit air into the water during the recoil. This air separates from the water in the air dome and takes the place of the air that is absorbed by the pressurized water in the dome.