How to Calculate Positive Displacement Pump Brake Horsepower

POWER ZONE Resources | Calculations

Formula:

BHP = Q × P / (C × n)

Where:
BHP = Brake Horsepower in horsepower
Q = Flow Rate in gallons per minute
P = Pressure in pounds per square inch
n = Efficiency expressed as a decimal
C = A conversion factor depending on units of flow and pressure

Units Value of C
GPM / PSI 1714
GPM / Hd. Ft. 3960 / SG
Barrels per Day / PSI 58773
Barrels per Day / Hd. Ft. 135788 / SG
CFM / PSI 229.16
CFM / Hd. Ft. 529.45 / SG
Cubic Meters per Hour / PSI 6.4875
Cubic Meters per Hour / Hd. Ft. 14.989 / SG

* SG = Specific Gravity of the fluid

Horsepower [HP] = Flow Rate [GPM] × Pressure [PSI] / (C × Efficiency)

Example #1:
Flow Rate = 750 GPM
Pressure = 125 PSI
Efficiency = 78%
Calculate: 750 [GPM] × 125 [PSI] / (1714 × 0.78) = 70.12 HP

Example #2:
Flow Rate = 125,000 BBL/Day
Pressure = 798 Hd.Ft.
SG = 0.75
Efficiency = 81%
Calculate: 125,000 [BBL/Day] × 798 [Hd.Ft.] / {( 135,788 / 0.75) × 0.81} = 680.2 HP

Note: The calculation above is only for single acting plunger and piston pumps. In a double acting plunger pump, the flow rate should be multiplied by 2. In a double acting piston pump, a modified piston diameter should be used where DP = 2 × DPiston – DRod

Where:
DPiston = Diameter of the Piston in inches

DRod = Diameter of the Drive Rod connecting to the piston

NOTE: These calculations and the information provided on this page is for reference only. Power Zone Equipment is not responsible for errors or incorrect calculations when applied to real life projects. Please use this information with care. For engineering assistance and design of equipment systems, please contact Power Zone Equipment.

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