ask-tom-pictureEditor’s note: This month we have a new twist for the Ask Tom column – Tom is asking a question to Walter Harrill of ‘Imaldris Farm about ram pumps — a pump that uses the energy of falling water to pump some of that water to a higher level, without an electric or gas pump. If you have ever lived in an older house you may have heard pipes rattle when you shut off the water quickly. That “water hammer” is caused when the water moving in the pipe is suddenly stopped and crashes into the back of the closed valve. The hydraulic ram pump was invented in the 1770s. It works using the same basic idea that when moving water that is suddenly stopped, it creates a high pressure zone behind the valve. The ram pump allows a portion of that moving water to be lifted by that high pressure to a location above the pump. Yes, that’s correct. Water “flows uphill” when a ram pump is involved — without the need for electricity or gasoline. The “catch” is that most of the water moving in the pipe is released back to the stream so only a fraction of the moving water is lifted.

Dear Walter,

During this exceptionally hot summer our electric bill is much higher than normal. To help deal with this problem I am looking at super-insulation for our produce cooler and a hydraulic ram pump to reduce pumping for irrigation. I understand that you did some work with hydraulic ram pumps. What is your favorite design?

— Tomram pump

Water Harrill wrote Tom that the best resource that he found in research about two years ago is from our neighbors at Clemson University.

Walt goes on to say “We built ours out of PVC plastic pipe (polyvinyl chloride available at building supply stores) using thicker schedule 80 for the drive line, I think this would be the best place to consider refit with galvanized steel pipe, as less flexible pipe yields a higher cost a little over $100. I believe it had a 1″ inlet and 1/2″ outlet. Of the entire set-up, the only moving parts (and therefore, about the only parts liable to wear out) are the two check valves Note that these are “swing” check valves, not “spring” check valves. We ended up replacing them on approx. a quarterly basis since grit in our water scratches the seal between the gate and it’s housing, allowing water/pressure to escape.

Our biggest challenge was a continuous water source – we were using the overflow from our reservoir fed by the spring, so any time that we used a bunch of water; someone had to hike up the mountain to restart the system. The good news is that at this point, the system is already primed, so it’s a 30 second process to get it going again (initial priming can run 15-30 minutes).

A few added notes from Walt –

I skipped the 1 1/4″ valve labeled (1) in the graphic above. It increases friction of the running water, decreasing the efficiency of the ram, and I just didn’t see it as necessary. The pressure gauge is very handy for the initial priming, since what’s required is cycling the ram by hand literally hundreds of times (pushing down on the gate of (4), letting the water push it back shut, pushing it down, letting it shut, etc) until it finally builds enough pressure to run on it’s on. 100psi would have been overkill for our system – we were primed at 17-18 psi and typically ran just below 30. The gauge just lets you watch it slowly climb, so you don’t get frustrated and give up, or alternatively, so you don’t keep going in spite of some small leak that keeps it from building pressure. A hard lesson, though, is that pressure gauges don’t do well left under pressure, so (10) is important, and I always removed the gauge once I had everything running and stored it in the shop.

The calculations for drive pipe length give you a wide range of “correct” possibilities (150 x drive pipe diameter to 1000x drive pipe diameter). Within that range, as you shorten the drive pipe, you increase the speed of the cycle, but shorter cycles seem to yield less pressure per cycle, so anything within that range gives you the same output. With that in mind, I lengthen the pipe to the maximum, so that I’m getting maximum pressure/cycle, and therefore reducing the number of cycles my valves are enduring, and hopefully, increasing the lifespan of the valves.

A few notes from Tom follow:

A hydraulic ram pump is powered by a body of water flowing downhill with a height difference. A general rule of thumb is that the water can be pumped 30 times as high as the available drive head (the height difference of the water driving the pump). So a head of 1 m can be used to pump up water to ~30m, while a 7 m head can pump water up to 210 m. With height difference, the actual difference in vertical height is meant, not the length measured along the slope, although excessive length can cause friction losses. (Tom’s note: This height can be measured with a transit or carpenters level on a pole.)

The capacity of a hydraulic ram depends on the scale of the pump, which is often measured in the diameter of the tube delivering the water to the pump. Pumps exist in the range 1″ up to 5″. The optimum length of the drive pipe is five-to-twelve times the vertical distance between the source and the pump, or 500-to-1000 times the diameter of the delivery pipe, whichever is less. This length of drive pipe typically results in a period between pulses of one-to-two seconds. A typical efficiency is 60%, but up to 80% is possible. The drive pipe is ordinarily straight but can be curved or even wound in a spiral. The main requirement is that it be inelastic, strong, and rigid; otherwise, it would greatly diminish the efficiency.

The source for the rules of thumb above is here.

Several Home Power magazine ram pump articles were assembled by Collier publishing with permission. Home Power is a great resource for small scale energy production consider subscribing here (PV, wind, hydropower, etc. — not just on ram pumps)

Here are some NCSU Extension links on possible permits needed to draw water from a stream.

Links on designing intake structures if you intend to use water from a stream:

http://www.microhydropower.net/basics/components.php#Weir
http://homepower.com/view/?file=HP124_pg68_Ostermeier

Many thanks to Walt Harrill for the practical experience behind this article. He has done OGS workshops on ram pumps in the past, so let us know if you are interested. Thanks

— Tom

Ask Tom © 2013 Tom Elmore & Organic Growers School

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Tom Elmore

Tom Elmore

Tom Elmore is co-owner and operator of Thatchmore Farm in Leicester NC. He has grown certified organic fruits and vegetables for 25 years and serves on the Boards of the NC Greenhouse Vegetable Growers Association and the Organic Growers School.