How do I select a hydraulic motor based on required torque?

Enter the required output torque (Nm), required shaft speed (RPM), gear ratio, and working pressure (bar). The calculator computes the minimum motor displacement (cm³/rev), standard motor size, required flow rate (L/min), and input power.

How does gearbox reduction affect hydraulic motor selection?

A gearbox increases output torque by the reduction ratio (i) while reducing the motor shaft torque requirement proportionately, allowing a smaller motor displacement to be used.

Is this calculator free to use?

Yes. This Kod5 calculator runs in the browser, requires no login, and is completely free.

Hydraulic Motor Selection by Required Torque

Information

Calculate minimum required hydraulic motor displacement, required oil flow rate, motor speed, and hydraulic power based on your application's required output torque and working pressure.

Sizing Principles:

Pressure drives Torque: Motor torque output depends directly on system pressure difference (Δp) and motor displacement (V).
Flow drives Speed: Motor rotational speed is governed by oil flow rate (Q) supplied by the hydraulic pump.
Gearbox Multiplier: Using a reduction gearbox reduces required motor torque and displacement by ratio (i), while increasing required motor RPM.

Note: Always consider mechanical efficiency (η_m ~ 85-92%) and volumetric efficiency (η_v ~ 90-95%) for realistic hydraulic motor sizing.

Inputs

Required Torque (T):

Torque Presets: 100 · 250 · 500 · 1000 · 2000 · 5000 Nm

Output Speed (n₀):

RPM

Gear Ratio (i):

Gear Ratio Presets: 1 (Direct) · 2 · 5 · 10 · 20 · 30

Gear Efficiency (η_g):

Working Pressure (Δp):

bar

Pressure Presets: 70 · 100 · 140 · 160 · 210 · 250 bar

Motor Mech. Eff. (η_m):

Motor Vol. Eff. (η_v):

Results

Motor Shaft Torque (T_m):

Motor Shaft Speed (n_m):

RPM

Min Displacement (V_req):

cm³/rev

Recommended Std Motor:

cm³/rev

Required Oil Flow Rate:

L/min

Mechanical Power Output:

Hydraulic Power Input:

Calculation Details

Hydraulic Motor Selection by Torque & Pressure

When engineering a hydraulic drive system, selecting the correct motor displacement starts with the required load torque and available system pressure. Unlike electric motors where speed dictates sizing, hydraulic motor displacement is directly proportional to output torque per unit of working pressure.

If your system utilizes a reduction gearbox between the motor and the driven load, enter the gear ratio (i) and gearbox efficiency. The gearbox multiplies the output torque, allowing a smaller, higher-speed hydraulic motor to generate substantial torque at lower final shaft speeds.

Key Sizing Formulas

Motor Shaft Torque: T_motor = T_req / (i × η_gear)
Motor Shaft Speed: n_motor = n₀ × i
Min. Required Displacement: V_req = (20 × π × T_motor) / (Δp × η_m)
Required Oil Flow Rate: Q = (V_req × n_motor) / (1000 × η_v) [L/min]
Mechanical Power: P_mech = (T_req × n₀) / 9550 [kW]
Hydraulic Power Input: P_hyd = (Δp × Q) / 600 [kW]

Engineering Selection Tips

Always select a standard commercially available motor displacement (e.g. 50, 80, 100, 125, 160, 200, 250, 315, 400, 500 cc/rev) that is equal to or slightly larger than the calculated minimum displacement V_req. This provides an extra safety margin for breakaway torque, cold oil friction, and peak mechanical shock loads.

Frequently Asked Questions

How do I calculate hydraulic motor displacement from required torque?

Formula: V (cm³/rev) = (20 × π × Torque in Nm) / (Operating Pressure in bar × Mechanical Efficiency). Divide this value by gearbox ratio if a reducer is installed.

What is the difference between mechanical and volumetric efficiency?

Mechanical efficiency (η_m) represents torque losses due to friction within motor bearings and swashplates. Volumetric efficiency (η_v) represents internal oil leakage past pistons and gears, increasing required pump flow rate.

Is this calculator free?

Yes. This Kod5 tool runs entirely in your browser, requires no installation or registration, and is free to use.