RA Mueller - Basic Formulas and Symbols (Cont.)

Pump Handbook

Basic Formulas and Symbols (Cont.)

Useful Formulas

NPSH

Net Positive Suction Head available (NPSHa) is the total suction head minus the vapor pressure (both expressed in feet absolute) at the pump suction flange.

NPSHa = 2.309(Pa - Pvp)/S.G. + or - He - Hf

Pa is the atmospheric or tank pressure (psi absolute), Pvp is the vapor pressure (psi absolute), He is the elevation head (negative if suction lift) expressed in feet and Hf is the friction loss through the suction piping expressed in feet.

HEAD

psi = (14.50)(bar)

psi = (.4912)(in. Hg)

psi = (.4331)(ft)(S.G)

in. Hg = (2.036)(psi)

in. Hg = (.8819)(ft)(S.G.)

1 atm = 760 mm Hg

1 atm = 29.92 in. Hg

ft = 2.309(psi)/S.G.

ft = (1.134)(in. Hg)/S.G.

CAPACITY

GPM = (7.481)(Cu. ft./min.)

GPM = (.2642)(Liter/min.)

GPM = (264.2)(Cu. meter/min.)

GPM = (4.403)(Cu. meter/hr.)

HPM

BHP = (GPM)(ft)(S.G.)/(3960)(E)

KWinput = (GPM)(ft)(S.G.)/(5308)(E)(M.E.)

E = pump efficiency M.E. = motor efficiency.

HP = (1.341)(KW)

KW = (.7457)(HP)

HP = (lb. ft.)(RPM)/5250

TEMPERATURE

deg. F = 9/5 (deg. C) + 32

deg. C = 5/9 (deg. F - 32)

Heat added to fluid due to pump inefficiency.
Total Heat (BTU per hr.) = (ft)(GPM)(S.G.)/1.557 (1/E -1)

Total heat added per pass through pump
in deg. F = (ft)/(778)(SH) (1/E - 1)
SH = specific heat value of liquid, E = pump efficiency.

LENGTH

(mm) = (25.40)(inches)

meters = (.3048)(ft.)

SPECIFIC GRAVITY

Water = 1.0 S.G. = 62.43 lb./cu. ft.

1 gallon water = 8.3453 lb.

1 cu. ft. water = 7.48052 gal.

VISCOSITY

Centistokes = (centipoise)/Specific Gravity

Above 50 centistokes, SSU = 4.55 (centistokes)

If over 2500 SSU, a centrifugal pump smaller than 2-1/2" is impractical. If over 5000 SSU, any centrifugal pump is impractical.