Definitions
Capacity 
Flow rate required, i.e., GPM, BPH, etc. 
Suction 
Pressure PSI or Head (ft.) 
Discharge 
Pressure PSI or Head (ft.) 
NPSH 
Available in absolute pressure 
Product 
Type liquid & its conditions
(temperatures, viscosity, specific gravity,
clean, solids, abrasive, corrosive) 
Type 
Centrifugal, rotary, reciprocatinggear,
lobe, screwhorizontal, vertical, inline,
submersible, self priming etc. 
Materials of Construction 
Desired materials and/or construction
features, if any 
Driver 
Electric/Air/Hydraulic motor  gas/diesel
engine  gas/steam turbine 
Formulas
 Head (ft.) = (psi x 2.31) / sp. gr. = (in.
Hg.) / (sp. gr. x .88)
 PS1 = (head (ft.) x sp.gr) / 2.31 = (.49 x in.
x Hg.)
 Velocity (ft./sec.) = (0.4085 x gpm) / [i.d.
(in.) of pipe] ^ 2
 BHP (Centrifugal) = (GMP x head (ft.) x sp.
gr.) / (3960 x pump eff)
 BHP Positive Displacement = (GMP X PSI) /
(1715 x pump eff.)
Conversions
Wt of Water 
8.34 lb./gal. or 62.37
lb./cu. ft @ 60 degrees 
1 lb./sq. in. 
2.31 ft. water (1.0 sp. gr.)

BPH x .7 
GPM 
BPD x .0292 
GPM 
1 BBL. (petroleum) 
42 gallons (U.S.) 
1 ft. water 
.433 PSI 
Atmospheric Press 
14.7 psi or 33.9 fr. fresh
water @ sea level 
1 inch of mercury (Hg) vacuum

1.133 ft. water 
Dynamic Suctions Lift (ft.) 
Vacuum in inches of Hg. /
(0.883 x sp. gr.) 
Net Positivie Suction Head (NPSH)
 NPSHr = head required @ the eye of the pump's
impeller to prevent cavitation, a function of
pump design.
 NPSHa = head available from the suction side
of the system, must always equal or exceed the
required (NPSHr) to prevent cavication.
NPSHa Factors Table
Positive 
Negative 
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
Effects on centrifugal pumps with limited change
of speed (RPM) or impeller diameter.
 Capacity (Q) varies directly as the speed (N)
or impeller diameter (D).
 Head (H) varies as the square of the speed or
impeller diameter.
 BHP varies as the cube of the speed or
impeller diameter.
 Law 1 = Q^1/Q^2 = N^1/N^2 or D^1/D^2
 Law 2 = H^1/H^2 = (N^1/N^2)^2 or (D^1/D^2)^2
 Law 3 = P^1/P^2 = (N^1/N^2)^3 or (D^1/D^2)^3
