## Conversions

Wt. of Water = 8.34 lb./gal. or 62.37 lb./cu. Ft. @ 60oF
1 lb./sq. in. = 2.31 ft. water (1.0 sp. Gr.)

1 ft. water = .433 psi
Atmospheric Press = 14.7 psi or 33.9 ft. fresh water @ sea level
1 inch of mercury (Hg) vacuum = 1.133 ft. of water
Dynamic Suction Lift (ft.) = vacuum in inches of Hg. divided (0.883 x sp. gr.)

## Cost of Pumping Water

Cost per 1000 gallons pumped:

.189x Power Cost per kilowatt-hour x head in feet

Pump Eff. X Motor Eff. x 60

## Formulas

 Head (ft.) = psi x 2.31 = In. Hg. BHP (Centrifugal) = CPM x head (ft.) x sp. gr. sp. gr. sp. gr. X .88 3960 x pump eff.
 PSI = Head (ft.) x sp. gr. = .49 x in. Hg. BHP (Positive Disp.) = GPM x PSI 2.31 1715 x pump eff.
 Velocity (ft./sec.) = 0.4085 x gpm Specific Gravity = Wt. of Liquid [i.d. (in.) of pipe]2 Wt. of Water

## Net Positive Suction Head (NPSH)

NPSHR = head required at the eye of the pump’s impeller to prevent cavitation, a function of the pump design.

NPSHA = head available from the suction side of the system, must always equal or exceed the required (NPSHR ) to prevent cavitation.

NPSHA FACTORS:

POSITIVE FACTORS                                                      NEGATIVE FACTORS

(1) absolute pressure on liquid                                    (1) vapor pressure of the liquid, absolute

(2) static suction head                                                 (2) friction & entrance losses

(3) static suction lift

AFFINITY LAWS: (Effect on centrifugal pumps with limited change of speed (RPM) or impeller diameter.

(1) Capacity (Q) varies directly as the speed (N) or impeller diameter (D).
(2) Head (H) varies as the square of the speed or impeller diameter.
(3) BHP varies as the cube of the speed or impeller diameter.

 LAW 1: Q1 = N1 or D1 LAW 2: H1 = ( N1 ) 2 or ( D1 ) 2 LAW 2: BHP1 = ( N1 ) 3 or ( D1 ) 3 Q2 N2 D2 H2 N2 D2 BHP2 N2 D2

Cubic feet x 7.48025 = U.S. Gallons              1 Gallon water = 8.3453 lbs.

U.S. Gallon x .1336 = 1.0 Cubic Feet                        1.0 Litre = .2642 Gallons