Courses/WorkshopsEnergy SystemsIrrigation

Ram Pumps

People are always fascinated by ram pumps. I think partly because they achieve the seemingly impossible task of pumping water to a higher height than the water supplying the pump, and they do it for no added energy input. This is often misunderstood as needing no energy, but even a casual understanding of the laws of thermodynamics tells us this is impossible. You will notice I said no added energy input because fundamentally what a ram pump does is harvest the energy of a lot of water flowing through the pump from a low head source to pump a much smaller volume of water to a higher head. Head being the height of the water relative to the pump.

Imagine if you will a pipe with an internal diameter of 100mm with water flowing through it. If the pipe is around 25 m long then the weight of the water in the pipe is close to 200kg, remembering that one liter of water weighs one kg. This is basically one of those large oil drums full of water.

Water is basically incompressible — meaning that you can’t fit more water into a container by cramming it in under pressure than you can just by pouring it in. So let’s imagine 200 L of water in an oil drum free falling under the influence of gravity. Next let’s imagine it hitting a concrete floor. For one thing the stop would be sudden and the force and the noise would be great. This is exactly what a ram pump does — the water falls through the pump gaining velocity until that velocity is sufficient to flip the waste valve shut. Suddenly you have a lot of water — which an instant earlier was traveling at quite a speed — stopping instantly. As you can imagine, with nowhere to go (like the concrete floor in our example), we have a lot of energy to dissipate.

By putting a one-way valve in a much smaller line coming off the main pipe we can use the energy in the main flow of water like a battering ram to punch the water past the one way valve and up the smaller pipe.

The energy of the sudden stop starts to dissipate as more water is pushed up the small pipe. Eventually the energy is exhausted and the water flow stops, and at this point the one-way valve shuts, trapping water in the smaller supply pipe, waiting for the next hammer blow of our watery battering ram. At this point the water in the main (drive pipe) is totally stopped and even starts to ‘bounce’  back just a little from the shock wave of the initial ‘hit’.

It is this reversal of flow which creates a small negative pressure in the pump which allows the waste or ‘clack’ valve to drop open via gravity and start the process all over again.

Now I want to go back to the point in the cycle where the water is pushing past the one-way valve and go into a little more detail, as I have, for the sake of clarity, left out a vital component of the system.

Attached to the outlet side of the one-way valve and branching of the delivery line we have a tank with air trapped in it. This tank’s job is to act as a shock absorber and smooth out the pressure spike of the ram. Without this tank the pressure spike can be so great it will impact on the service life of the pump. After the one-way valve is shut the pressurized air in the tank re-expands and continues to push water up the delivery pipe — greatly increasing the efficiency of the pump. Those tempted to do without the air tank be warned. Just to see what would happen I ran a 100mm diameter ram with only 1 meter fall and a lift of three meters and managed to tear a 50mm check valve to bits. Now the valve was a good quality, glass-reinforced plastic one rated to over 100psi. While I should have been mortified at the destruction of the valve I couldn’t help but feel an evil glee at the clear demonstration of the forces involved.

If ram pumps have a downside, the one that most often comes to mind is the need for a certain amount of fall, below which they won’t operate. Depending on size and other factors, minimum fall is between 500mm and 1000mm. We also need to realize that when it comes to energy there is no such thing as a free lunch, so how much fall we have directly effects how high we can pump. Typically most commercial rams are quoted as being capable of lifting water ten times the fall, so 1 meter of fall will give you 10 meters of lift. It also stands to reason that the higher we pump the less we will pump as we are having to use more energy simply overcoming the greater weight of water in the delivery pipe.

Recently I was presented with a challenging site, where the creek the client wanted to pump from had a maximum fall of 1 meter and the height we needed to lift the water simply to get out of the creek gully was 20 meters. From the numbers given earlier the upper range we could hope to pump to with a 1 meter fall is 10 meters, so it usually wouldn’t have been deemed possible. Then add in the factor that I was hoping to build the ram pump myself and that performance figures for other homemade rams was generally given to be in the region 5 meters lift per meter of fall — so the task looked all but impossible. The icing on the cake was that the creek was prone to flash flooding and to get any fall at all the pump would have to sit directly in the creek bed, right in the way of logs and such when it flooded.

It didn’t look good till I hit on the idea of staging two pumps to get us up and out of the gully.

The idea goes something like this: first we use our low fall (1m) to run a large ram pump and pump to a low delivery head (5m) and then let it fall through a smaller ram pump from the height of 5 meters back to the creek. This effectively gives us a small pump running with a fall of 5 meters which even on the lower end of the drive to head ratio (5:1) gives us enough to get up and out of the gully.

Luckily I even had a small pump that I had previously built and tested that I knew would do the job with the given fall. Perfect.

All that had to be done then was work out the volume of water required to run the small pump and then build a bigger pump to supply that volume with a little spare capacity. After a lot of research and some mid-range number crunching (not one of my strengths) I came up with a pumped sized to use a 100mm drive pipe. My target was 40 liters a minute delivered to 5 metres above the creek.

In the photo above you can see the pump design i came up with. Ram pump size designation normally comes from the diameter of the drive pipe — in this case 100mm. Going from left to right we can see where the 100mm drive pipe attaches then the main body of the pump (the big steel box) and then the waste valve (square opening) on the right.

An important design consideration is that we want the water to gain the greatest velocity possible, as the faster the water the more energy. This is especially important when we have very low falls as we have less energy to start with, so an important consideration is a straight flow path from the drive pipe inlet to the waste valve outlet. 90 degree turns and such will rob us of potential energy. Also we want the waste valve outlet to be at least as big as the pump inlet (remember we want maximum flow for maximum energy). To do this I worked out the cross sectional surface area of a 100mm pipe (78.5 cm2) and then cut the waste valve hole to be slightly bigger — 100mm x 100mm (100 cm2). I did this before actually sourcing the pipe, and, because we were using scrap, when it turned up it was actually 112 mm internal diameter, which is 113 cm2 cross sectional surface area. Unable to resist getting the absolute best out of the pump I remade the waste valve and opening larger so that once again it was larger than the inlet — so no flow restriction.

Again under the theme of getting the most energy, a waste valve that shuts early won’t allow the water to gain the greatest velocity and as we already know we have limited energy to start with so anything that interferes with that is a big no no. To that end we need a waste valve we can tune so that it closes just as the water is gaining its maximum velocity. Anything less is wasted energy.

It’s a bit hard to see in the photo but our waste valve is a heavy steel flap hinged at the bottom so it lays back into the oncoming flow of water. You can see the row of four small shiny bolts in the square waste valve opening — these attach the valve plate to a stainless steel door hinge. The valve drops open under gravity because the plate it is bolted onto is angled back. The adjusting bolt simply passes through the center of the valve plate (single big bolt in the square opening) and can be adjusted so the angle the water passes over the valve plate can be adjusted. We’ve all stuck our hands out a car window and made those wavelike motions up and down and you will have noticed it’s easy to keep you hand horizontal to the air flow but the instant you angle up or down a larger force flips your hand up or down rapidly. This is exactly what happens with our valve.

Of equal importance to all I’ve written about so far is the need to use rigid materials for the drive pipe and the pump body. The reason these pumps work at all is to a large degree due to the incompressibility of water. So imagine our 200L liter barrel falling towards the floor except this time it’s a large tractor tube filled with water. For a start we will get more of a splat than a crash, and there won’t be any chipped concrete, that’s for sure, and that’s because the energy of the falling water is to a great degree dissipated by the elasticity of the rubber tube. So it is with our drive pipe and pump body. If we make them out of materials that have some ‘give’  in them, then we are wasting energy by flexing those materials. You will see lots of ram pumps on the internet using plastic parts for the drive pipe and the pump bodies. These certainly work well if we are in a situation where we have enough energy, so we can afford to waste some of it. Ultimately, however, if we are talking maximum efficiency, then rigid materials like steel are best. In the end it comes down to what you need and what it costs. For us we needed steel because of our low head and also for durability as this thing will, over the course of its life, have whole trees coming downstream and smashing into it — so plastic pipe just doesn’t cut it.

Most of the designs you will see on the internet tend not to be designed to sit right in the stream bed, and certainly most aren’t designed to have logs and boulders crashing into them, so they tend to have air tanks that stick straight up from the pump body so that they can trap air in the top of the chamber to act as a shock absorber — generally with a device called a snifter valve that lets a tiny gulp of air into the chamber each time the pump cycles. This is so that air under pressure isn’t gradually dissolved into the water in the pump (just like CO2 into a bottle of soft drink). This would then make the pump act like it had no air chamber, with the result of lower performance and far greater stress on the pump parts.

Anyway, as you can imagine in a flood, air chambers that stick up will tend to get damaged far easier than ones that lie flat, so we designed ours to lie flat. This required that instead of a snifter valve we trap air in the chamber using a different method, because, for one, a snifter valve doesn’t work well with a low air chamber. Secondly our pump is sitting right at water level so the minute the water level rises and the snifter valve goes under, the air chamber will fill with water and the pump stops. We got around this simply by filling a car tube with air and stuffing it in our air chamber so the air was trapped in the car tube and couldn’t dissolve away, with the result that the pump will continue to run under water as long as we still have sufficient fall.

The air tank in the photo is salvaged from an old LPG vehicle tank, and the fitting on top of the tank is just the original from when it was in a car — it is retained purely to seal the tank. You can also see water starting to build up velocity as it exits the waste valve.

Another important factor in getting the most out of a ram pump is the length of the drive pipe — too short and you don’t get enough mass going . Think of it like this; you have two battering rams, one is a telephone pole and the other is a pool cue. Both are made out of wood, but we know which one will bash down a door. So you need the biggest reasonable mass of water you can. I say ‘reasonable’ because over a certain length and you will actually start to lose performance again. It’s a Goldilocks thing — not too big, not too small, but just right. This has to do with the interactions of the various shock waves traveling up and down the pipe and certainly is not something I’m going to go into great detail on. Luckily we have a rule of thumb calculation that we can use to come to the correct lengths. Take the internal diameter of the drive pipe and multiply it by 150 and that will give you your minimum length. Next take the internal diameter of the pipe and this time multiply it by 1000, which gives you your maximum length. Now if you have a longer drive pipe run, because of site conditions, don’t fret. You can put in a stand pipe, which is simply a pipe coming vertically off the drive pipe. If we do this towards the effective maximum length of the drive pipe as you’ve calculated it, then this will allow the pressure waves to dissipate and the pump retain its maximum efficiency.

Let’s recap regarding factors effecting efficiency.

Fall. Get the maximum fall of water into the pump. At 1m we’re right at the bottom of what is considered viable. In fact, for 100mm ram pumps generally, 1.5m is considered the minimum viable fall.

Rigidity. The pump body is vastly overbuilt because the scrap steel we had was very thick (12mm) so is very rigid, however other factors can effect rigidity — like any leaks in the drive pipe and the material the drive pipe is made of. Here we had some issues. Firstly the gasket material for fitting between our lengths of drive pipe was salvaged conveyer belt and was too hard and didn’t seal properly. Also after our initial run the pressure spike in the drive pipe found some internal weak points where the pipe must have been nearly rusted through. Every time the waste vale shut we had water from various leaks shooting skyward. We now have better gasket material ready for instillation and our local scrap guy has his eye out for some replacement pipe.

Tuning. We have adjusted the long bolt so that the water builds to nearly maximum velocity before shutting. A simple test is to observe how far the water is gushing out the waste valve with the valve held fully open with a stick — this is our maximum velocity. Next, observe how far the water gushes out when the pump is running. If it’s substantially less than when the waste valve is held open, then adjust till it’s nearly as much. Too much though and it won’t shut reliably. A word of caution — don’t hold the waste valve open with you finger…. Here we can go back to my original analogy and imagine what would happen if your finger was caught between a falling 200kg drum of water and a concrete floor. Ouch!

Drive pipe length. Here we’re actually under our minimum length, and, as already mentioned, the pipe is leaking, so it’s definitely sub-optimal. So, we’re waiting on our scrap guy!

Pressure/Air tank. Here we’re good. Best practice is to size the tank to 50 times the pumped volume of one cycle of the pump, which for this size pump is around one liter. The tank is about 60 liters, so that’s good to go.

I suppose the next question is how did it all go, considering our target of 40LPM and a few suboptimal factors?

As I stated at the start, due to boyish enthusiasm we fired it up prior to finishing the air tank and destroyed the check valve, so we knew we had harnessed some substantial energy. Or should I say we hadn’t harnessed it, hence the rupture. Once the air tank was finished and installed we primed the pump and started it up. A flow test at 5 meters gave us 36LPM. Considering the performance tweaks we know we have to address we will easily hit our target of 40LPM. Happy is not the word — we were stoked!

Next we installed a pressure gauge in the delivery line to see what our maximum delivery pressure was. We topped out at over 70 PSI (sorry for the imperial measurement but I’m a PSI kind of guy).

This gives us a maximum theoretical pumping height of 49 meters. This means we could actually get up and out of the gully in one lift. Before you get too excited though it is still to be assessed wether we could match the flow rate of the second stage pump to get the ultimate flow rate we required without the staging. But if its over 4LPM we’re in business!

It was about this time that a loud whooshing sound was heard and the air tank took off down the creek spraying a jet of water out the back. We had salvaged the old damaged valve and put it back together, and under the strain of the pressure test it finally gave up its life for the greater good. A quick trip to town and a nice new brass valve was soon installed.

This shot shows removing the gauge after the pressure test.
The water was shooting at least 15m vertically.

Considering all the adverse factors, some of which we will shortly correct, I think it’s fair to say that the pump construction and installation is and will be a resounding success and will become a vital part of the property’s infrastructure.

On my next post i want to explore some intriguing possibilities for ram pumps. Hint. What set of circumstances would allow you to take water out of a creek or stream and yet increase the volume of water flowing in the creek?


  1. good day,we have a deepwell can we put also a rampump?estimate 1500liter / min.fresh water from 100feetkind regards pidrus

  2. I really enjoyed this article! Ram pumps were always a bit of enigma to me; needless to say, they are now a well-understood piece of appropriate tech after this excellent article. Thank you.

  3. I have a pump that works on water pressure but does the same work as a Ram. It is called a Highlifter and costs $750.00 but has been working flawlessly for me for 20 years.

    1. Hi Randal. The piston style pumps work well and can pump to very high heads the highlifter looks to be a beautifully made pump. The Australian Glockman is another of this breed. Last year we did some experiments with a ram pump using a dirty water source which had a better fall to pump a nearby clean water source. It worked but efficiencies were woeful . This was primarily due to the need for increased precision and optimisation in the manufacture of the parts required and this is where the more efficient but more mechanically complex piston rams are a little limited. I built the latest ram with a welder a grinder and a drill. While i used commercial non return(check valves) you can and i have fashioned these from all sorts of weird and wonderful readily available materials. So the mechanical precision needed is low. I know i left behind me people that having seen me do it can do it themselves and thats what i’m ultimately trying to do. Having said that just in the last few days i’ve mentioned to a few people that the next step is using ram pumps to compress air and i have been looking very hard at piton or diaphram style pumps as they may be the best way of achieving this although being the simple is best type of guy i am i’m trying for a design that uses the simpler “old school” rams at this stage. By the way how often are you changing your seals and how does the highlift handle abrasives in the water ?

    1. Hi Rodger yes tromps are great unfortunately you need a lot of fall to generate the required pressure to run common air tools, if you look at the height of the balance tube on any given trompe this will indicate its potential to compressed air. So we would need a fall and balance pipe length of 70 meters to get 100psi. I’m looking at more modest heights of a meter or so that are obviouslt more common and more within the range of the possible for individuals. Cheers

  4. How much noise does it make, I am buying a 10 acre property just north of Kyogle with a fast flowing stream,which would be perfect for a ram pump Most ram pumps are noisy, can your design be run underwater. .

    1. Hi Beau. The pump is actually pretty quiet as the valve seats onto some conveyor rubber. And yes the pump will run under water although as the water rises you will have reduced fall and so eventually the pump will stop.

  5. I have not been able to do by measurements yet.
    However to get more head (2.5 meters) Could I use 50 meters of 63mm polypipe connected to 10 meters of 60mm steel pipe, then connect the ram pump.
    I would use a standpipe at the beginning of the steel pipe.

    1. Hi Beau 10 meters for the drive pipe is about the minimum (150 x 60mm = 9000 mm) so that will be fine especially as you also have 50 meters of poly behind that. And yes a standpipe or a small barrel would be a good idea. Are you farbicating your own pump body or assembling one out of plumbing fittings ?

      1. Hey Tim we would like to do a ramp pump. The water needs to be moved about 200m.up a hill. Crazy but could it be done. What kind of fall would we need? We can use machinery.
        Cheers Lauren

    1. Hi Beau the property where the ram pump is situated gets winter rain and usually uses a spring high on the landscape for drinking water however the volume of water was very low and stops mid summer. The ram was made to take advantage of the fact i was on site and happy to do the work. The coming spring season will probably see the ram hooked up to supply the whole farm. The plan is to run it through biosand and charcoal filters to treat the water to the highest possible standard and run the whole farm on this supply.

  6. Hi Guys, I have been using rams since 1963, several different types. For the past 26 years I have used a 2″ Wilcox and have observed it in just about every condition from drought to 5M deep flood down our 800 drop to the Goulborne River. I am rebuilding it now for the 4th time, replacing bearings valves and shaft. The main casting is still fine but the airspring elbows and snifter need an upgrade. I am getting quotes from some CNC equipped friends for an upgraded design, heavier bearings that should run 10 years in mineralised water rather than the current 5-6 years. If you or anyone here would like to know more about getting one, or spares for the existing type, please get in touch. Economies of scale mean that if i just make one or two they will be pricey, but if I can justify making 10 or more the price can come right down. These rams last for 50 years or more if looked after (and this one has had 5 ton+ boulders flipped in its path by the floods) so we know the design is pretty well thought out and extremely robust.
    We pump 5000 liters a day up 80M thru 20mm AG pipe 1.5 Km long, with a supply fall of 4M and drive pipe of 12 M. We use about 80 liters of water per minute from the stream, about half the flow, most of the year. When it gets really dry, we throttle back the stroke, increase the rate to 120bpm from about 85 and get about 3500 L/day.
    This takes 5 minutes to adjust.
    At the end of the drought 2009 the stream dried up for two months. Apart from that, fantastic.
    Hope to hear from you.

    1. I am interested in the design of the ram pump you have. Do you have any drawings?
      I would like to fabricate one, I have CNC capability

  7. Hi Harry, what size diameter is your drive pipe?
    How do you throttle back the stroke on a ram pump similar to the one in this article.
    Beau Lyons australia

  8. Tim, your article is awesome and inspired me to set about a making a pump like yours as I couldn’t justify the up front cost of a solar bore pump, panels and batteries. I have a stream like the one you describe heaps of volume but little fall. I’ve gone with a 100mm drive pipe 24m long with a 1.5m fall but am going to attach a 44 gal drum at the end to help funnel water into the drive pipe. I’ll be pushing up a 25mm ag pipe with a head of approx 40m over 250meters (thought I’d get higher with a 1″ instead of 2″ delivery pipe). I’ll be happy with 4 litres per minute if I can get it. One thing I can’t get from your article is how full the tyre bladder in the air tank needs to be. I’m using an old 45kg LPG cylinder and think I might have to use smaller tubes like bike or motorcycle tyres to get then inside the 50mm hole in the top. Is there a guide to how much of the tank needs to be filled with air inside a tube? or is it just a matter of getting some air in there?
    The other thing I can’t work out is does the waste flap need to lie flat when open or be parallel with the bottom of the pump or will the adjusting bolt naturally hold this up off the bottom so water can catch under and flip it closed? I’ve gone with a 45degree angle for the back plate that the waste flap is attached to so it will travel in an arc less than 45 degrees.


    1. Hi Stephen that sounds awesome. We actually made a flange and welded it to the air tank that way we had a bigger opening and were able to get a car tube in there we pumped the tube up so it was firm but not super tight. Here is a good link with some specs for sizing the air chamber . i was also interested in using tennis or squash balls as they would be pretty durable. Remember that as you have a very small head everything has to be as rigid as possible to get the lift. Two inch would not make any difference to your pump output if anything in some circumstance it would offer less restriction to flow and you would pump more however in this case due to your pumped head that will not be an issue. 40 meters is getting right on the edge of what is practical as we were getting 75-80 PSI which theoretically should give us a stall height of 49 meters so at 40 you will be getting very little flow. Still a small 25 mm ram supplied by the 100 mm so that you are staging up to your 40 meter will do it easily if needed. I set up the waste valve so the flap was parallel with the flow through the pump and then gradually adjusted it more and more open until it would not close reliably and then adjusted it back up till it was closing reliably so as to get the biggest pulse. This means a slower cycle rate but the maximum water hammer effect. Keep me posted of your progress.

      1. Tim, thought I’d follow up with some progress reports. Put the pump into service and Version 1 was a bit flakey. Discovered that you need an airtight seal to get the flap to open again reliably. I used hard rubber on the waste plate and it wasn’t a good seal. Back to the workshop and Version 2 of the pump is now in action. We cut the box in half to reduce the volume and used a silicone gasket to create an airtight seal. Not sure how long the silicone will last with the pounding so may need to go to version 3 with an engineered waste plate with proper ‘o’ ring that I can periodically replace. Have also made a 200kg concrete panel I will mount the pump and tank to so it doesn’t ‘walk’ down the creek. We’re getting 15 litres per minute through a 25mm discharge pipe lifted 6 meters (see video at link below). Our intake is 100mm gal pipe running 36m over a fall of approx 1 meter. I’m installing some rock gabions in the creek to raise the water level another 500mm or so and hopefully improve flow but already stoked with the approx 20,000 litres per day. Here is a link to some photos where you can see I’ve totally copied your design – royalties to follow!!!



        1. Hi Stephen AWSOME JOB ! No royalties needed just keep playing. Yes it’s important to get the plate sealing well. I carefully filed the plate as flat as i could. I used old hard conveyor rubber and it worked great but what i did was mount the rubber so it acted as the gasket for the end of the pump body and just had an opening cut for the waste water. This way the seal is not mounted on the waste plate and not subject to as much distortion. I seriously suspect an “O” ring won’t last long. The other thing is to make sure the waste plate hinge is shimmed so the plate is perfectly flat in the closed position or even slightly low so the hinged edge touches just before anywhere else as the force generated will insure it it makes a good seal. But don’t over do it as too much will leak. I found the conveyer rubber good as it a nice balance between durable but is soft enough for a good seal with good set up and quietens the pump nicely.
          Again great work and please keep me posted. Ps it looks a hell of a lot tidier than my one.

  9. Hi Tim,
    Great info on the ram pump. One of the previous posts mentioned wanting to use a ram for pumping from a well, and this caught my attention since I don’t have any running water to speak of (only a small stream that dries up in august). Would it be possible, in your experience/opinion, to drop a pipe down a well through a pitless adapter whose outlet feeds into a buried pipe extending down a hill to a ram pump station many meters below the static water level in the well. My idea would be to start a siphon via hand pump, then once the flow started, let physics take care of the rest to pump water back up to my homestead. Is there any reason why this wouldn’t work?

  10. Greetings
    I would like to mention to waste water as a very important factor to improve the Ram pump inefficiency , thinking how to use the waste water to operate another ram pump, or by recycling the waste water to water source ( for my case the water source is a concrete canal of 2M width x 2M highte
    Please let me know your comments
    Best regards

  11. Hi Tim. Thank you for writing such an indebth article about a tool that can really be a game changer when it comes to using water effiently and to save money.

    My name is Roberto and I have an interesting situation on my island in Puerto Rico. Basically I have access to a natural spring where a two inch metal tube comes out the side of a slope that leads to a creek. My question is if I can basically hook up the ram pump intake to this spring and be able to send water from there to feed sinks, showers, and irrigation.

    I could use help with this design and I am wondering if there are products in the market that could help me.

    Thank you for your time and god bless.

  12. I have about 3m of fall over 40m of pipe will this be a problem (the only site for the ram pump). 2″ in 1 3/4″ out to pump. trying to pump about 15m up over 60m of poly, how well do you think this will work???

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