Page 238 - Applied Photovoltaics

photovoltaic applications, mainly for low flows from deep wells or for domestic
water supply pressurisation. The diaphragm requires frequent replacement but this
type has the advantage that it can run dry without damage.

Figure 11.9. Performance curves of a free-diaphragm pump (Used with
permission of Halcrow & Partners, 1981).

The best known volumetric pump is the reciprocating piston type (‘Bucket’ pump),
which is the sort used in hand pumping. These can be powered by hand, diesel, wind
or electricity, but as with other volumetric pumps, they suffer from poor efficiencies
below heads of 10–20 m (Halcrow & Partners, 1981). They are available for use with
photovoltaics, commonly with the motor at the surface and the energy transmitted
down the bore by a shaft. However, the coaxial balanced piston pump uses a
submersed motor (von Aichberger, 2003).
Vane pumps (Platt & Little, 2001) are another alternative, principally for low flow
rate applications such as domestic supply pressurisation or circulation of water in
solar thermal heaters (Fig. 11.10). Fig. 11.11 gives the performance curves of a
typical rotary positive displacement pump.

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