Hydraulic Power Fundamentals

Hydraulic power is the energy transferred by fluid flow under pressure. The power depends on both the flow rate (volume per time) and the system pressure (force per area).

Hydraulic Power Formula

The theoretical hydraulic power output is:

P_hydraulic = P x Q

• P = System pressure (psi or bar)
• Q = Flow rate (GPM or LPM)
• P_hydraulic = Hydraulic power output

Input Power (HP) Calculation

The mechanical input power required at the pump shaft accounts for pump efficiency losses:

HP = (P x Q) / (1714 x eta)

Where 1714 is the conversion constant for psi, GPM to HP. For metric:

kW = (P_bar x Q_LPM) / (600 x eta)

Efficiency Breakdown

Overall pump efficiency is the product of two components:

eta_overall = eta_v x eta_m

• Volumetric Efficiency (eta_v): Accounts for internal leakage losses (typically 85-98%)
• Mechanical Efficiency (eta_m): Accounts for friction and mechanical losses (typically 90-98%)
• Overall Efficiency: Combined effect (typically 75-95%)

Motor Sizing Guidelines

Electric motors should be sized with a service factor to handle:

• Pressure spikes during system operation
• Cold start conditions (high viscosity)
• Continuous duty operation

Typical service factor: 1.15 to 1.25 times calculated HP