The hydram is an automatic pumping device powered by falling water. The hydram uses a large amount of water falling through a small height, to lift a small amount of that water to a much greater height.
Each cycle happens very quickly, about 60 times a minute or once a second (although the cycle can be between about 30 and 120 times a minute). Since the cycle happens very quickly it is easiest to explain how it works by looking at the four stages:
When the waste valve is open, water flows down the drive pipe and comes out the open valve. The water flowing past the open valve drags past it, trying to close it. The flow down the drive pipe through the impulse valve gets accelerates. As it gets faster, it drags harder on the valve until it is strong enough to drag it closed.
When the waste valve closes, the water flowing down the drive pipe cannot escape through it. At the moment valve closes, the water is travels very fast and suddenly it has nowhere to go. As the water increased speed, it gains momentum. Since the water cannot escape, the momentum changes to pressure-energy and the water in the pump body compresses. This leads to a sudden rise in pressure, called a “water hammer”. The water pressure rises to a much higher level that the pressure in the pump’s air chamber.
Because the pressure rises higher than the pressure in the air vessel, the delivery valve is pushed open and water flows through it. The pressure in the pump body drops quickly to equal the pressure in the air vessel. The water coming down the drive pipe slows down and the pressure in the pump body drops. As soon as the pressure falls enough to be lower than the pressure in the pump’s air vessel, the delivery valve closes. The delivery valve is a one-way valve, which stops water flowing back from the air vessel into the pump.
When the delivery valve closes, there is still some pressure in the pump body and drive pipe. The valves in the pump are closed, so the only direction in which the water can move is back the way it came. The water coming down the drive pipe has stopped, so the pressure energy can be released by moving back up the drive pipe. The water in the pump body bouncing back makes the pressure in the pump body fall low enough for the waste valve to reopen. The waste valve reopens because of its own weight. The low pressure in the pump body means that a small amount of air is sucked in through the snifter valve. This air waits under the delivery valve until the next cycle when it will get pushed into the pump’s air vessel. This makes sure that the air vessel always stays full of air.
Figure. Ram Pump Installation at Badegaun, Godawari
During each pumping cycle only a small amount of water is pumped. Most of the momentum harvested from a large amount of water is transferred into a small amount of water. The high pressure in the pump body pushes water through the delivery valve and into the air vessel. It provides the power to push the small amount of water much farther uphill than the big amount of water fall downhill.
While a hydram is working, water flows out of the waste valve. This happens during the ‘acceleration’ stage of each pump cycle. It is the noise of the “water hammer”, the splashing of water, and the closing of the waste valve that people notice when they see a working hydram. The noise varies from pump to pump. The water leaving the waste valve is often called ‘waste’ water. Although ‘waste’ water is not delivered by the hydram it is the movement-energy harvested from this water that pumps the water that is delivered. A better name for ‘waste’ water would be ‘used’ water.
Figure. Ram Pump Installation at Badegaun, Godawari
Components Of A Hydram And Their Functions
- Intake: structure at source that diverts flow of water to the hydram system;
- Feed pipe or canal: delivers water from the source to the drive tank;
- Drive tank: provides storage to ensure a constant flow to the hydram and removes sediment from the water;
- Drive pipe: feeds water to the hydram;
- Hydram: pump unit that delivers a small amount of the drive flow to the delivery pipe;
- Pump house: to protect the pump and fittings from accidental damage or theft;
- Delivery pipe: delivers water from the hydram to the delivery tank;
- Delivery tank or pond: stores the water pumped by the hydram. Can be a cement based structure or a lined pond;
Distribution system: distributes water to the users. Piping can take water to households, tap-stands or fields.
Starting a pump
Although ram pumps often start very easily they can require a little coaxing particularly the first time that they are run. Procedure varies according to drive head in the system with large drive head requiring extra care to starts a pump.
- Open the waste vale fairly quickly.
- Water will flow out through the open waste valve until it suddenly shuts.
- If waste valve automatically reopens, the pumps should continue to run on its own. Some time you need to reopens the waste valve until it creates delivery head.
If waste valve does not reopen automatically for long time, you must prime the delivery system manually by filling the delivery pipe until sufficient delivery head is available for the pump to operate.
Figure. Installed Ram Pump at Dhungkharkha, Kavre
Source: Centre for Rural Technology/Nepal(CRT/N). All right reserved to CRT/N.