How many HP is a GPM

It cannot be determined by the flow rate in gallons per minute (GPM) alone what is the horse power rating of a hydraulic pump. Horsepower is a measure of motor or engine’s power output and it is calculated using an explicit equation that takes into consideration factors such as speed of the motor and torque. The horsepower rating of a hydraulic pump will depend on its motor or engine, design, pressure and flow requirements for the system to which it is being applied.

To find out the horsepower rating of hydraulic pumps, one needs to know how fast fluid flows through them at specific pressures as well as their mechanical efficiencies. Using these knowns, one can use a performance curve for hydraulic pumps to determine what levels of horsepower are produced by 10 GPM at 1000 PSI. It should be observed that due to different operating conditions in systems, HP rated against given flowrate and pressure may not be equal to the maximum HP rating.

For example; let us suppose you have a hydraulic pump with a flow rate of 10 gallons per minute (GPM) and it operates at 1,000 psi pressure. You also have information about this device’s efficiency which stands at eighty percent (80%) and its source energy being driven by five horse powered electric motors. To calculate pump’s horsepower rating at 10 GPM with working pressure set up to 1000 PSI; first we need to know output power because we are interested only in inputting numbers into mathematical formulae:

Output Power = Flow Rate * Pressure / Efficiency

Output Power = (10 GPM * 1,000 PSI) / 0.8

Output Power =12,500 ft-lbf/min

Next we need to convert this output power into horse powers using conversion factor from foot pound force per minute:

Horsepower= Output Power/ Conversion Factor

Horsepower=12,500 ft-lbf/min/33,000 ft-lbf/min/hp

Horsepower=0.38 hp

Therefore, in this example the horsepower rating of the hydraulic pump would be 0.38 HP at a flow rate of 10 GPM and pressure of 1000 PSI and as noted earlier; it is necessary to realize that this horse power rating could be different from maximum HP rating but this will depend on operating conditions within the system.