Pump Basics
Maintenance Log


This page outlines a few fundamental concepts you should find useful when working with our pumps. It covers the main pump types describes performance characteristics and factors and provides a quick look at how horsepower requirements are calculated.

Types of Pumps

Engineers describe pumps based on the kind of motion they utilize displacement mechanism cylinders, and pressure.

Reciprocating pumps convert rotary motion to linear motion. Pump speed in rpm determines the pumps output volume for any given combination of cylinder bore and piston stroke.

Positive Displacement pumps are used to move liquids or compress gases. They operate on a what goes in, must come out principle.

Reciprocating Positive Displacement pumps may use plungers with static seals pistons with dynamic seals or liquid diaphragms to achieve their pumping action.

Output may also be a function of the number of cylinders a pump possesses. Commonly, pumps will feature up to six cylinders. Terms like simplex (for one) and triplex (for three) indicate the number of cylinders a particular pump features.

A pump increases a fluids pressure when it forces that fluid through a restriction. When the result exceeds 150 psi, it is termed high pressure.

Performance Characteristics

Crankshaft bearing life, volumetric efficiency, and inlet flow curve are three performance characteristics of practical significance in many if not most pump applications.

Crankshaft Bearing Life is a function of lubrication, speed, and load. This last factor is calculated as follows:

Plunger Area (in square inches) x Pressure (psi) = Plunger Load (in pounds)


((?Plunger Diameter in inches)2 x p) x Pressure (psi) = Plunger Load (in pounds)

Volumetric Efficiency compares the pump is actual output to its theoretical output. If there were no losses in the pumping system, its flow would equal:

Area x Stroke x Number of Cylinders x Crankshaft Speed
                                 231 in3 /gallon
= gpm

Dividing the actual flow by the theoretical value calculated above will yield a value which, taken as a percent, indicates volumetric efficiency. Valve timing is a major factor in achieving good volumetric efficiency. This timing is affected by the relationship among poppet weight, Ceramic Tile spring rate, poppet travel distance, plunger speed, and plunger diameter.

Inlet Flow Curve relates volumetric efficiency to specific inlet pressures. General Pump provides inlet flow curve charts for all its pumps, on request.

Horsepower Requirements

Because different types of Indium Ingot prime movers vary in their pumping performance capabilities, the horsepower required to achieve a given output depends on the energy source.

Hydraulic power is more efficient than either electric power or internal combustion.

Various requirements may be calculated using these relationships:

Hydraulic horsepower required = Pressure x Flow / 1714

Brake horsepower (electric) required = Pressure x Flow / 1457

Gas engine horsepower required = Pressure x Flow / 1100

To learn more basic pump theory, be sure to attend one of General Pumps training classes. Sessions are offered throughout the year on a first-come, first-served basis and are free-of-charge to our Plastic Business Cards customers!


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