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.
The beat valve is the heart of the ram. The number of beats per
minute can be set by the amount of lift the valve is allowed. The
greater the lift, the slower the beat, but the stronger the jet of
water that is sent up the delivery pipe. A shorter lift will beat
faster, but reduces the height to which the ram will lift. Any ram
that needs a spring to help the beat valve to start to open does
not have the proper drive pipe ratio.
One seventh of the total amount of water that is passing through
the ram can be lifted to a height of five times the height of the
fall. A smaller amount of water can be lifted to a height of thirty
times the height of the fall. For the best efficiency, the drive
pipe should be laid at an angle of about ten degrees and should be
of a length that is sixteen times the height of the fall. To
achieve something close to this in my model, I coiled the drive
pipe. This ratio provides the maximum potential power for the water
to strike the greatest hydraulic blow in the ram body. The water
flowing through the pipe is governed by the law of falling bodies;
they gather impetus the longer the distance traveled. This is a
simplified explanation of why a long inclined drive pipe is used
instead of a vertical one, where the head (or fall) would be the
same. The weight of the water is greater in the inclined pipe.
Rams were actually quite efficient. Efficiency tests on rams in
England showed a maximum efficiency of 83%. American catalogs
claimed 90% efficiency.
Now for my model ram. Drawings were published for a model
English style ram in a 1919 edition of the English magazine, Model
Engineer, which I obtained through ‘inter-library
services’. I then made the patterns, coreboxes, and castings to
the dimension shown in the article. I did change the delivery valve
to one of a mushroom design as this was easier to make. The ram has
a 5/16‘ diameter opening, and the pulse
valve opening must have at least the same area. The angle valve and
pipe fittings are from Coles’ Power Models and are their ?’
fittings. The delivery pipe has an opening of 0.150′ diameter.
A hydraulic ram works best when pumping against pressure, so to
start the ram, it is best to close the valve completely first.
After the air has been flushed out of the drive pipe, the ram is
started by pressing down on the beat valve a few times. The ram
then continues to run automatically. At this time the angle valve
is opened a little, and water begins to be pumped back into the
tank. The operating speed and amount of water pumped can be
governed by adjusting the lift of the beat valve with the two nuts.
To stop the ram, stop the beat valve and lift it closed. This shuts
off the water flow. Press it down, and the ram starts again.
My supply tank is 28′ high to the tank bottom, and the stand
is made of PCV pipe legs. The drive pipe is ?’ copper tubing,
15 feet long, coiled to save space. The tubing has a 1
3/32‘ inside diameter. This gives me the
5/16‘ diameter needed plus some
additional space to offset the fact that there are bends in the
line and internal friction.
A ten inch length of flexible plastic hose connects the copper
tubing to the ram. While a flexible connection on a full size ram
hinders its operation, on a model ram it actually improves the
operation because it helps to introduce elasticity into the draw
pipe to assist the rebound or pulsing action of the water. This is
the result of scaling down nature. My ram measures 2? long by 1
9/16‘ wide by 4?’ high. It was a fun
project to make and a very easy machining job. The subject of the
hydraulic ram is a fascinating one since it is close to getting
‘something for nothing’ from the water. If anyone has an
interest in building a model ram, I did make a few extra sets of
castings and have made my own drawings.
