Select Page Terms, Technology, and Formulas

AMPERE: A unit of intensity of electric current being produced in a conductor by the applied voltage.

FREQUENCY: The number of complete cycles per second of alternating current; e.g., 60 Hertz.

HORSEPOWER: The rate at which work is done.  It is the result of work done (stated in foot-pounds) divided by the time involved.

INERTIA: The property of physical matter to remain at rest unless acted upon by some external force.  Inertia usually concerns the driven load.

MOTOR EFFICIENCY: A measure of how effectively the motor turns electrical energy into mechanical energy.  Motor efficiency is never 100% and is normally in the neighborhood of 85%.

POWER FACTOR: The ratio of the true power to the volt-amperes in an alternating current or circuit or apparatus.

SERVICE FACTOR: A safety factor in some motors which allows the motor, when necessary, to deliver greater than rated horsepower.

SYNCHRONOUS SPEED & SLIP: The speed of an a-e motor at which the motor would operate if the rotor turned at the exact speed of the rotating magnetic field.  However in a-e induction motors, the rotor actually turns slightly slower.  This difference is defined as slip and is expressed in percent of synchronous speed.  Most induction motors have a slip of 1-3%.

TORQUE: That force which tends to produce torsion or rotation.  In motors, it is considered to be the amount of force produced to turn the load.  It is measured in lb.-ft.

VOLTAGE: A unit of electro-motive force.  It is a force which, when applied to a conductor, will produce a current in the conductor.   Basic Formulae and Symbols PUMP SYMBOLS

GPM = gallons per minute

Lb = pounds

Hr. = hour

Sp. Gr. = specific gravity

H = head in feet

psi = pounds per square inch

In. Hg. = inches in mercury

hv = velocity head in feet

V = velocity in feet per second

g = 32.16 ft./sec.2 (acceleration of gravity)

A = area in square inches

I.D. = inside diameter in inches

BHP = break horsepower

Eff. = pump efficiency expressed as a decimal

N = speed, RPM

Ns = specific speed

Nss = suction specific speed

D = impeller in inches

NPSH = net positive suction head

NPSH^ = net positive suction available

Pa = atmospheric pressure in psia

Pvp = vapor pressure in psia

w = specific weight of liquid in pounds/cu. ft.

hs = total suction head ft.

Q = capacity in GPM