ROTARY DIRECT LIFT DEVICES
It generally improves both efficiency and hence productivity if the water lifting element
can move on a steady circular path rather than being cycled or reciprocated. The reason
for this is that the energy input to any water lifting device is usually continuous, so that if
the output is intermittent, unless energy can be stored during the parts of the cycle when
no water is lifted, it is lost. Therefore reciprocating/cyclic devices tend to be less efficient
than rotary devices; this is not a firm rule however, as some reciprocating devices
include means to store energy through the non-productive part of the cycle while some
rotary devices are less efficient for other reasons.