This is a sketch of a diaphragm-type reciprocating pump:

The diaphragm pump is an offshoot of a plunger pump. Because of the risk that contamination could travel between the plunger and the cylinder, the diaphragm is safer for microbial processing. This applet is crude but shows how a reciprocating piston (plunger) pump works. The flywheel that moves the plunger can attach the arm to the plunger at various points to change the amplitude of the stroke and thus the pumping rate. The pumping rate can also be changed with a different rotational speed, but variable speed motors or mechanical means of changing rpm are expensive.

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