சுதர்சன் சாந்தியப்பன்

Most of us are not aware of a type of domestic water pump called the Compressor pump. I had come across this noisy pump a couple of year ago. The operation of this pump is very simple and powerful though it is noisy. The pump consist of a Air Compressor and a nozzle. See that’s all. Remember in jet pumps we would have an Impellor and a Jet (a form of nozzle). Compressor jumps compresses atmospheric air and pressurized that thru the nozzle which creates a back pressure to pull water for far depths to the surface and above. The advantage is that the compressor (motor + compressor) is no way connected to water drawing system other that at the nozzle. Whereas in jet pumps water is drawn by the back pressure created at the impeller’s center (radial flow) which makes it apparent that water is always in touch with the motor + impeller system. In jet pumps there are two pipes down to the water level one for drawing and one of recycling. Jet pumps push a portion of drawn water downwards to create back pressure at the jet-nozzle. Water flows from bottom to impeller, impeller to top, impeller to bottom again. In compressor pumps, the since air is pushed downwards water flows only from bottom to top.

In a compressor pump, the flow of water does not start immediately because the water starts flowing only after a certain amount of pressure is built at the nozzle. Also the flow of water is not uniform typically the pump pushes gush of water in regular intervals of time at like a jittery saw tooth waveform. Since a compressor is needed, these pumps are noisy. In a Jet pump, the water flow is more or less uniform and the water pumping starts immediately once the pump is switched on. Here water level is maintained in the delivery pipes and also at the impellor system. Jet pumps are almost quite when all the bearings and move parts are properly lubricated.Disadvantages are found in both systems. In a jet pump, water is always expected to be maintained at the impellor system. The water level is maintained by a spring driven valve at the jet below water level. During the passage of time, this spring and valve gets damaged which is defy the requirement of impeller water level. So one has to fill in water everytime to start the pumping action. Jet pumps dont work at all when there is a lot of slime around the jet or if the valve is stuck due to any particles near it.

In a compressor pump, if there is a leak in the downstream air flow, water pumping does not happen as the pressure could not built at the nozzle. When the strength of the compressor falls below a threshold again the water pumping stops for the same reason. These pumps are very noisy (both reciprocating and centrifugal). The pumps needs regular maintainance as they have more mechanical moving parts (basically the compressor oil needs to changed on a regular interval). Also, upstream water flow should not be blocked completely which would affect the nozzle, so it is not possible to close the gate valve in the upstream when the pump is running. Whereas the upstream
of jet pump can be completely shut even when the motor is running.

Compressor pumps are more suitable for borewells with depths of range 200+ feet. Jet pumps are more suitable for wells and sumps. Compressor pumps can work even when there are dirt or dust in the water as the pressure at the nozzle would push them away from blocking the channel. Jet pumps are good when the nozzles are suspendable well above the surface level in the well. In the case of bore well, jet pumps are fine if casing is done for the entire depth. Compressor pumps are atleast 1.2 times expensive than Jet pumps in Chennai.In general when you go for deeper borewell, it is always adviced to go for pvc continuous hose pipes instead of discrete pipes with joints. It serves two purposes. 1) Maintenance is easy as it would relatively very easy to take out the entire hose out of the bore as you can roll it. 2) Two many joints in the upstream/downstream deteriotes the performance of the pump.