Hydraulic motors
Orbital (gerotor) hydraulic motors, piston motors and gear motors: components that turn pressure into continuous rotation and provide a drive without a gearbox.
The simplest way to drive a slow turning shaft that needs high torque is often a hydraulic motor: a single component replaces the electric motor and gearbox. For mixers, conveyors, winches and agricultural machinery we select the hydraulic motor from a speed and torque calculation, and build the circuit with the pump and valve that will drive it.
Types
Orbital (gerotor) hydraulic motors
The inner gear rotor moves eccentrically inside the outer ring and delivers high torque at low speed. The most common type for gearless drives in conveyors, mixers, sweeper brushes and agricultural machinery.
Heavy duty orbital motors
A larger bearing and shaft design carries axial and radial loads. Used for wheel drives and winch drum drives.
Piston hydraulic motors
Radial and axial piston types. Used in heavy duty applications that need very high torque, or high speed and efficiency.
Gear motors
The motor counterpart of the gear pump. Used in high speed, low torque drives such as fans and small conveyors.
Product images: hidroticaret.com and manufacturers.
How to select
Selection starts with displacement: the volume of oil the motor takes in per revolution. With the same flow, a small displacement motor turns fast with low torque, and a large displacement motor turns slowly with high torque. Speed is found from flow and torque from pressure. The table below gives calculated values for the motor series we hold in stock.
The second deciding factor is the shaft and mounting geometry: a parallel, splined or keyed shaft, the flange type and the bolt hole dimensions determine whether the motor fits the machine. For a replacement, these dimensions are needed as well as the displacement.
The return line needs attention in the circuit. When a motor is stopped under load, it keeps turning through inertia. If the return line is closed, the motor cavitates internally or a pressure spike occurs. For drives that hold a load, a brake or a load holding valve is selected, and for rotation in both directions a suitable directional control valve.
Speed and torque of orbital hydraulic motors
| Displacement | Speed at 40 L/min | Torque at 150 bar |
|---|---|---|
| 36 cm³/rev | 1,111 rpm | 86 Nm |
| 50 cm³/rev | 800 rpm | 119 Nm |
| 80 cm³/rev | 500 rpm | 191 Nm |
| 100 cm³/rev | 400 rpm | 239 Nm |
| 160 cm³/rev | 250 rpm | 382 Nm |
| 200 cm³/rev | 200 rpm | 477 Nm |
| 250 cm³/rev | 160 rpm | 597 Nm |
| 395 cm³/rev | 101 rpm | 943 Nm |
Calculation: speed = flow × 1000 ÷ displacement; torque = pressure × displacement ÷ 20π. These are theoretical values; motor efficiency reduces the actual speed and torque slightly. The displacements are taken from the orbital motor series we hold in stock.
Frequently asked questions
How do I calculate hydraulic motor speed?
Speed is flow divided by displacement: with a flow of 40 L/min, a 100 cm³/rev motor turns at about 400 rpm.
Hydraulic motor or geared electric motor?
A hydraulic motor has the advantage if the machine already has hydraulics, if space is tight, if the load is subject to shocks or if the speed needs stepless adjustment. For a single fixed speed drive on a machine without hydraulics, a geared motor can be more economical.
Can a hydraulic motor run in both directions?
Yes. Orbital motors turn in both directions. The direction depends on which port the oil is supplied to and is selected with a directional control valve.
My hydraulic motor has slowed down and lost power. What is the cause?
The internal leakage of the motor may have increased, but the same symptom can also come from pump wear or a leak in a valve. We find the cause by measuring the flow and pressure in the circuit.
Do you also build the circuit that drives the motor?
Yes. We select the hydraulic motor together with the pump and the directional and flow control valves that drive it. If required, we manufacture it as a hydraulic power unit.
Stock, sizes and part numbers
Sizes in stock, manufacturer part numbers and brands are kept up to date in our catalog. Send us your requirement on WhatsApp or by e-mail and we will quote and ship worldwide.