Hydraulic Formulas for Motors and Pumps
Hydraulic Formulas for Motors and Pumps: Essential Calculations for Optimal Performance
Although motors and pumps can look similar, they do different jobs in a hydraulic system. Pumps use an external power source, such as an engine or electric motor, to create flow, while a hydraulic motor converts pressurised flow into rotational force.
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What these formulas help you calculate
- Displacement (cc/rev)
- Motor speed (rpm)
- Torque (Nm)
- Hydraulic power (kW)
- Flow rate (L/min)
Key Differences Between Hydraulic Motors and Pumps
Purpose and energy conversion
- Hydraulic pumps convert mechanical energy into hydraulic energy by creating flow and pressure.
- Hydraulic motors convert hydraulic energy into mechanical energy, producing rotary motion and torque.
The formulas below help calculate performance metrics such as displacement, torque, speed and power. If you are using these calculations to specify a replacement or new drive component, browse our hydraulic motor range alongside your system requirements.
1) Displacement (cm³/rev or cc/rev)
Displacement helps determine how much fluid a motor or pump moves per revolution. This is important when matching motor speed and available flow.
- D = Displacement (cm³/rev)
- Q = Flow rate (L/min)
- N = Motor speed (rpm)
2) Motor speed (rpm)
Motor speed is calculated from available flow and displacement. A larger displacement motor will usually run slower at the same flow rate.
- N = Speed (rpm)
- Q = Flow rate (L/min)
- D = Displacement (cm³/rev)
3) Torque (Nm)
Torque is one of the most important values when selecting a hydraulic motor, especially for low-speed, high-load applications.
- T = Torque (Nm)
- D = Displacement (cm³/rev)
- ΔP = Pressure drop across motor (bar)
Once you know the torque your application requires, compare suitable options in our low speed high torque hydraulic motors category.
4) Hydraulic power (kW) from torque & speed
This formula helps estimate output power when torque and motor speed are known.
- P = Power (kW)
- T = Torque (Nm)
- N = Speed (rpm)
5) Hydraulic power (kW) from flow & pressure
Hydraulic power can also be calculated from flow and pressure, helping you check whether the system can supply the power required.
- Ph = Hydraulic power (kW)
- Q = Flow rate (L/min)
- ΔP = Pressure difference (bar)
6) Flow rate (L/min)
Flow rate helps determine motor speed and overall system performance. Always check that the available flow matches the motor’s operating range.
- Q = Flow rate (L/min)
- D = Displacement (cm³/rev)
- N = Speed (rpm)
Flowfit can help with hydraulic motor & pump calculations
If you’re unsure about sizing, performance calculations, or selecting the right component, our Technical Sales team can help you choose the best solution for your system. Browse our low speed high torque hydraulic motors or get in touch for expert advice.
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