II. FUNDAMENTALS OF OPERATION
A. How a reciprocating pump works
A reciprocating pump is a positive displacement mechanism, liquid discharge pressure being limited only by the strength of the structural parts. Liquid volume or capacity delivered is constant regardless of pressure, and is varied only by driver speed, speed reduction, and/or plunger/piston size changes.
Reciprocating motion is imparted to a plunger/piston by a slider crank linkage which results in a piston motion closely approximating simple harmonic motion, as shown in Appendix B. This reciprocating motion alternately lowers the pressure in front of the plunger/piston when filling the pump, and increases the pressure when emptying the pump. The incoming liquid opens the suction/inlet valve. At the same time the discharge valve is held closed by the downstream line pressure. Outgoing liquid closes the inlet valve and opens the discharge valve. This simple mechanism provides high volumetric efficiency, approximately 95 percent, for most incompressible liquids.
Characteristics of a WGI reciprocating pump are;
(a) positive liquid displacement
(b) high pulsations caused by the sinusoidal motion of the
plunger/piston
(c) high volumetric efficiency
(d) high mechanical efficiency
(e) low pump maintenance cost
