A little stream runs through the farm – actually its a drainage channel, cut into the rock to drain this part of the bog, well over a hundred years ago. The fields and woods drain into it, and it heads off through the countryside which is mostly level. As it passes through our land, it falls by a couple of feet, and you can hear it burbling away behind the polytunnels. The water is coloured a brown colour by the peat (and possibly by the iron in the rocks). It has always looked like a useful source of water but until now, I assumed there wasn’t enough to make it useful, and anyway, how would we get it from the bottom of the stream to the polytunnels above.
This is where the ram pump comes in. For the uninitiated, a ram pump is an entirely mechanical pump, that uses the energy in flowing water of a stream to lift a small amount of that water. For every 1 foot of fall (or head, as its known) in a stream, it can lift water up about 8 foot or more.
How it works
Water enters the pump through a drive pipe, which is typically a rigid pipe, between 20 and 100 foot long. It passes into the pump and out through a normally open one way valve. The friction of the water causes the valve to shut. The water has nowhere to go – it can’t go back up the pipe, so it passes through a second normally closed one way valve, and off up the delivery pipe to wherever it is being pumped. This takes the pressure off the first valve, which falls open again. The water begins to flow out of it again and the cycle begins once more. During each cycle, about 90% of the water flows out of the first (waste) valve, and about 10% goes through the second (drive) valve. A pressure vessel is typically added so that the water flowing out of the pump builds up some pressure to smooth out delivery.
There are a few rules of thumb to bear in mind:
You need at least a foot (ideally four or more) head of water. It seems to just about work with a foot.
The length of the drive pipe needs to be at least 150 x the diameter of the pipe, and no more than 1000 x the diameter of the pipe. The pipe needs to be as rigid as possible, because it is the shock wave of the closing and opening valves that drives the pump, and any flexibility in the pipe will absorb some of that, reducing the effectiveness of the pump.
The drive pipe should be about twice the size of the delivery pipe.
The waste valve seems to work better as a flap valve, and I’ve used flap valves in both, but some people use a spring valve for the drive valve. Some use spring valves for both. The flap valves are cheap though.
I used a gas bottle as a pressure vessel and it seemed to work as well as using a proper pressure vessel with an inflatable bladder inside, but the proper pressure vessel has the advantage of having adjustable pressure.
Here I am testing the pump. It needs to be fed from a body of water (ie a bucket) – NOT from a hosepipe, as the pressure from the hosepipe will overcome the shock wave in the drive pipe and prevent it from working properly. To start the pump, you shut the valve on the delivery side, hold the waste valve open to let air out, and then release it. It might take a couple of pokes at the waste valve to get the pump to start, but once its going, it will continue as long as there’s water in the reservoir supplying it.
Here it is set up in the stream, working away quite happily. It took me pre-filling the drive pipe with water from a hose to get the air out, before it would get going properly.The pipe needs to have an even(ish) downhill slope to prevent air getting trapped in it. I put some plastering mesh over the inlet to prevent debris going down the pipe and clogging the pump, and the end of the drive pipe is held in place with a large rock, as the water comes out of a culvert.
The pump is set at the lowest point I have, in order to maximise the head of water. It remains to be seen whether the waste valve stays above water in heavy rain conditions but we’ll soon find out.
and here’s what comes out of the delivery pipe. It will definitely need tested and then filtered before we begin dosing the polytunnel with it. Initially I got about 25 litres an hour out of the pump but after having it run for 24 hours, and making adjustments to the drive pipe, I’ve got that up to around 60 litres per hour. Mainly by making sure that the open end of the drive pipe is well under water (at least 3 inches), and by ensuring the pipe had no high spots on its way down.
Next steps:
I’ll probably make a better job of the inlet, damming the culvert to raise the water level slightly. I also have to raise a 1000litre IBC up to about 1 metre high so that we can then run the stored water through a basic filter, into a drip irrigation system.
Thanks for posting this, looks doable at our place here.
It’s easy to check whether its feasible – measure the flow by timing how long it takes to fill a 5 gallon bucket, (or similar), and try to measure the fall of the stream. A low fall will need a longer drive pipe, a higher fall, a shorter drive pipe. For a 1″ pipe your drive pipe might be between 4m and 20m long. You’re going to get about 10% of the water out of the pump that goes through it, so the flow rate will give you an idea of whether you have enough to be worth it. This one pumps 12 times higher than the fall of the supply (so about 12 foot), and does nearly a litre a minute (ish).
Hi ref ram pump. How long is feed from culvert to pump and higher is culvert to pump ,thanks bu rain
Hi, its about 15 yards from culvert to pump, maybe a bit more, and the drop from the culvert to the pump is about a foot maximum. Right on the limit of what will work.
cheers
Steve
Thank you for sharing the details.
Please may I ask where one might buy a flap valve – it’s a term that doesn’t seem to show up in any plumbing suppliers lists.
Best,
Elliot
Hi, I got mine here – https://www.ebay.co.uk/sch/m.html?_ssn=plumbingsuppliesonline12&LH_PrefLoc=&_from=R40&_trksid=p2499338.m570.l1313&_nkw=flap+valve&_sacat=0
as I couldn’t get one locally.
The water source for my proposed Ram pump is a brook which is now about 1m deep but in heavy rain over a period it rises to at least 3m.
I can see all my work disappearing down the brook.
Have you any suggestions ?
Does pressure vessel size affect the pumping rate?
No, as far as I can tell, it is just the flow rate into the pump that affects the pumping rate. The pressure vessel just damps the pressure wave so that the valves aren’t damaged.
A hydraulic ram pump will pump approximately 30 times its working fall in height i.e from level of spring water (drive water) to the waste valve. The bigger the drive pipe and waste valve coupled with a bigger air vessel will pump more water depending on spring or stream availability. Obviously the drive pipe can’t be too long as you’ll get frictional loss and it won’t shut the waste valve properly.I have a formula that will tell you how much it’ll pump in 24 hrs. Fall (ft) x waste gpm (spring) x 900 divided by the lift (point of delivery height)
I work on pumps that lift water 600ft vertically. I have made a home made pump like yours for fun but in 2” galv fittings. Tee, two non return valves and a large air vessel. Eg 10ft fall or head x waste let’s say 30gal per min and a lift of 100ft
10x30x900 divided by 100 that’ll be a delivery of 2,700 gallons in 24 hours. Depending on the size of your drive pipe.
So if you have 10ft fall you could pump to 300 ft but not much delivery. I you reduce the height of the delivery pipe say 250ft above the ram it’ll deliver more water.