If you have a duplex double acting reciprocating pump making 190 strokes/minute, with a 4" diameter cylinder, a 8" stroke and operating with 75% volumetric efficiency, what is the capacity of this pump?
β’ Formula for capacity of a reciprocating pump in gallons per minute (gpm) based on cylinder area, stroke length, and strokes per minute β’ Meaning of duplex and double-acting in terms of how many displacements per stroke you actually get β’ How volumetric efficiency changes the theoretical capacity
β’ First, compute the volume displaced by ONE side of ONE cylinder in one stroke, using the diameter and stroke length. Then convert cubic inches to gallons. β’ Figure out how many such displacements happen per minute for a duplex double-acting pump. Does each stroke move water on one side or both sides of each piston? On one or two cylinders? β’ After getting the theoretical gpm, apply the 75% volumetric efficiency to find the actual capacity, then compare with the choices.
β’ Confirm the correct area of the cylinder using the 4" diameter: remember to use radius, not diameter, in the area formula. β’ Confirm what duplex (two cylinders) and double-acting (both sides of piston pumping) do to the total number of pumping actions per stroke and per minute. β’ Be sure to apply the 75% volumetric efficiency AFTER calculating the theoretical capacity, not before.
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