How to Make a Hand Pump
Most types of groundwater pump have a piston that moves back and forth inside a two-valve cylinder (a valve allows water to pass in only one direction - in this case, upwards):
Suction pumps have the cylinder situated above ground or near the surface. This means that they can only be used for shallow wells. It is called a suction pump because pulling up on the piston creates a low pressure ("suction") in the cylinder, causing the atmospheric pressure outside to push the water up to the surface. Because atmospheric pressure is fairly low, the pressure difference between inside and outside the cylinder is only large enough to raise water from a maximum depth of about 7 metres.
It should also be noted that if a shallow-well is used too much, the water-table may fall as the underground reservoir of water is reduced. If this level falls below 7 metres, the pump will not work.
Four types of shallow-well pumps are shown below: rower, piston, diaphragm and semi-rotary.
The rower pump is a simpler and cheaper version of the traditional piston pump (see below). Its simple design means it can be easily manufactured and maintained using locally available skills and materials. This type of pump may require "priming", which means pouring water into the cylinder so that the seal around the piston is airtight. It is very important that clean water is used, to avoid contamination of the pump and the spread of water-borne diseases.
Piston pumps, based on the same design as shown in Figure 1, are more widely used. There is a similar risk of contamination from dirty priming water. In cases where the water is to be delivered under pressure (such as to a village water mains) or to a point higher than the cylinder (such as a water storage tank), a "force" pump is required. The operation is the same, but the design is slightly altered so that the top is airtight. This is done by putting a valve on the spout and adding a "trap tube" and air chamber which maintains the pressure (and therefore the flow) during the up-stroke.
This design is often used for fuel pumps in cars. The Vergnet pump is an adaptation of this principle for deep-well use, which can be used in crooked wells, where a rod-operated pump would have problems, and which is fairly easy to maintain.
References and further reading
This Howtopedia entry was derived from the Practical Action Technical Brief man-Powered Water-Lifters.
To look at the original document follow this link: http://www.practicalaction.org/?id=technical_briefs_water
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