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A coil pump is a simple, low-cost pump consisting of a rotating coil of hollow tubing partially submersed in a fluid. One end of the coil is left open at the outside diameter of the coil, with the other end bent in towards the center of the coil and exiting in a straight line with the coil axis. This end of the coil is equipped with a rotating seal which presses against the pump's discharge pipe. As the coil rotates, the open end scoops up fluid each time it dips into the fluid body, with the rotary action moving the fluid through the coil and out of the discharge pipe. Although these pumps are only capable of delivering low heads, they are extremely cost effective and require minimal energy to drive, making them ideal for rural agricultural irrigation applications.
Originally developed as an alternative to the Archimedean screw type pumps used in many developing nations to irrigate crops, the coil pump offered the benefit of horizontal operation with equal or better head capabilities. The Archimedean screw has to operate at approximately 30° to the horizontal, requiring very specific installation site ground plane profiles. The inclined attitude of these pumps also reduces the number of practical drive options possible. The coil pump, on the other hand, runs horizontally, allowing the pump to be installed on the same plane as the fluid body and not on an incline. It is also easy to construct and maintain from readily-accessible, cheap materials and requires minimal effort to drive.
A basic coil pump consists of a coil of tubing, typically PVC hose, supported on one end by a drive disc. The end of the tube adjacent the drive disc is left open at the outside diameter of the coil. The opposite end is bent in at right angles towards the center of the coil, and then at right angles again to exit along the coil axis. This allows this end of the coil to revolve around its own axis in a static position. It is equipped with a seal that rotates against the discharge pipe of the pump, forming a watertight seal between the pump and discharge circuit.
The entire coil is partially submersed in a fluid body, generally a lake, pond, or river. As the coil rotates, the open end dips below the fluid surface at regular intervals, scooping up a quantity of fluid at each pass. This fluid is then forced through the coil by the rotational forces, eventually passing through the sealed end and out into the discharge circuit. Although the coil pump can't achieve impressive head values, the design's reliability, low cost, and ease of maintenance make it an ideal irrigation and general rural pumping option for developing nations.