TABLE OF CONTENTS WILLIAM K. CHAPLIS
FREDERIC W. BUSE
A power pump is a positive displacement machine consisting of one or more cylinders, each containing a piston or plunger. The pistons or plungers are driven through slider-crank mechanisms and a crankshaft from an external source. The capacity of a given pump is governed by the rotational speed of the crankshaft.
Unlike a centrifugal pump, a power pump does not develop pressure; it only produces a flow of fluid. The downstream process or piping system produces a resistance to this flow, thereby generating pressure in the piping system and discharge portion of the pump. The flow fluctuates at a rate proportional to the pump speed and number of cylinders. The amplitude of the fluctuations is a function of the number of cylinders. In general, the greater the number of cylinders, the lower the amplitude of the flow variations at a specific rpm.
All power pumps are capable of operating over a wide range of speeds, thereby making it possible to produce a variable capacity when coupled to a variable speed drive. Each pump has maximum suction and discharge pressure limits that, when combined with its maximum speed, determine the pump's power rating. The pump can be applied to power conditions that are less than its maximum rating but at a slight decrease in mechanical efficiency.
The power pump is a positive displacement device. When operating, it will continue to deliver flow independent of the pressure in the discharge piping system.
