Hydraulic Motors

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What is a Hydraulic Motor and Why Do You Need It?

A hydraulic motor converts hydraulic energy into mechanical energy: a rotating shaft. It uses hydraulic pressure and flow to generate torque and rotation.

You can use hydraulic motors for many applications, such as winches, crane drives, self-driven cranes, excavators, mixer and agitator drives, roll mills, etc.

Note: The design of a hydraulic motor and a hydraulic pump are very similar. For this reason, some pumps with fixed displacement volumes can may also be used as hydraulic motors.

How DTA Can Help You:

DTA has extensive expertise with hydraulic motors and carries a substantial inventory of motors from several major vendors. Depending on your requirements, DTA can supply high-quality hydraulic motors, taking into account a wide variety of functional and hydraulic system requirements.

DTA supplies hydraulic motors from high quality manufacturers, such as Calzoni, Denison Hydraulics, Parker, and Staffa Kawasaki. We can provide premium build hydraulic motors, as well as motor spare parts, service and installation manuals.

Different Types of Hydraulic Motors

The hydraulic motor must be geared to hydraulic system requirements; issues such as load, range of load, speed, serviceability, etc. must be taken into account. There are different types of hydraulic motors, as noted below:

Hydraulic Gear Motors

  • Hydraulic Gear Motor
  • Epicyclic Gear Motor

Hydraulic Vane Motors

  • Balanced Vane Motor

Hydraulic Piston Motors

  • Axial Piston Motor
  • Radial Piston Motor

Part-turn Actuators

  • Rotary Actuator
  • Rack and Pinion Actuator

The power produced by a hydraulic motor is determined by the flow and pressure drop of the motor. The displacement and pressure drop of the motor determines the torque it generates. The power output is thus directly proportional to the speed. The motors range from high speed motors of up to 10,000 rpm to low speed motors with a minimum of 0.5 rpm.

Note that low speed hydraulic motors are designed in such a way that large torques are generated at low speeds. High speed motors have better operational characteristics at speeds that are at least higher than 500 rpm.

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Hydraulic Gear Motors

Hydraulic gear motors are often used in mobile hydraulics and in agricultural machinery to drive conveyer belts, dispersion plates, screw conveyors or fans.

There are two different types of hydraulic gear motors. The gear motor, which is very similar in design to the external gear pump, is a high speed motor. The epicyclic gear motor, also known as an orbit or gear ring motor, is a slow speed motor.

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Hydraulic Gear Motor

Gear motors and axial piston motors are high speed motors. If your operation requires a lower speed, you can reduce the output speed of the shaft by using gears. The operating pressure of gear motors is usually quite low: between 100 and 150 bar. Modern gear motors, however, are capable of operating at continuous pressures of up to 250 bar.

Key features of gear motors:

  • Low weight and size
  • Relatively high pressures
  • Low cost
  • Wide range of speeds
  • Wide temperature range
  • Simple and durable design
  • Wide viscosity range

A major drawback of gear motors is that they produce a large amount of noise. Gear motors with only one direction of rotation are designed exactly the same as external gear pumps. A gear motor that can change directions of rotation has a drain case port and the axial pressure fields are different. The efficiency of gear motors is relatively low due to oil leakage.

Typical parameters are:

  • Displacement volume: 3 to 100 cc
  • Maximum pressure: up to 250 bar
  • Range of speeds: 500 to 4,000 rpm
  • Maximum torque: up to 400 Nm

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Epicyclic Gear Motor

Epicyclic gear motors are also called orbit motors, gear ring motors or gerotor motors. Unlike gear motors, the orbit motor has very low oil leakage. The motor can produce large torques at very slow speeds (approximately 5 rpm).

Key features of epicyclic gear motors, gear ring, orbit or gerotor motors are:

  • Low oil leakage
  • High torque at low speeds
  • Large displacement volume
  • Relatively small size
  • Low noise level

Just like gear ring pumps, the rotor of the orbit motor has one tooth less than the stator. Because of the difference in teeth, enclosed chambers are formed within the orbit motor.

Epicyclic gear motors or orbit motors are available in two types: one has a central shaft and the other has a cardan shaft. Orbit motors with central shafts are widely used in hydraulic systems.

The orbit motor with a cardan shaft consists of cylindrical rolls in the set of gear wheels. It is only used for special applications (e.g. high pressures, very high efficiency and longer lifespan).

Typical parameters:

  • Displacement volume: 10 to 1,000 cc
  • Maximum pressure: up to 250 bar
  • Range of speeds: 5 to 1,200 rpm
  • Maximum torque: up to 4,000 Nm

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Hydraulic Vane Motors

Hydraulic vane motors are used in both industrial applications, such as screw-drive and injection moulding, and mobile applications, such as agricultural machinery. Hydraulic vane motors have less internal leakage than gear motors and are therefore better suited for lower speeds: about 100 rpm minimum. The maximum operating pressure of hydraulic vane motors is between 100 and 140 bar, and they�re used in both hydraulics and pneumatics.

Key features of hydraulic vane motors are:

  • Low noise level
  • Low flow pulsation
  • High torque at low speeds
  • Simple design 
  • Easy serviceability
  • Vertical installation friendly

In order to operate correctly, the vanes of the rotor have to be pressed against the inside of the motor housing. This is generally taken care of with spiral or leaf springs, but rods can be used as well. This precaution prevents issues with stationary motors, such as the vanes sinking into the grooves and causing the oil to flow over it instead against it. Most often, the rotor is hollow, thus enabling it to be easily mounted on a spline shaft.

Typical parameters:

  • Displacement volume: 9 to 214 cc
  • Maximum pressure: up to 230 bar
  • Range of speeds: 100 to 2,500 rpm
  • Maximum torque: up to 650 Nm

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Hydraulic Piston Motors

Hydraulic piston motors are used to drive mobile and construction equipment, winches, ship-cranes, and all kinds of heavy-duty hydraulic equipment for offshore and onshore operations.

Hydraulic piston motors combine high speeds with large displacement volumes at higher operating pressures. If your operation requires a significant amount of power, a hydraulic piston motor is the best option. Whether your heavy-duty installation needs high torques or high speeds determines the choice of either a radial piston or axial piston motor.

Multi-stroke piston motors increase displacement substantially because each piston carries out multiple strokes per revolution of the shaft. Hence, a hydraulic multi-stroke piston motor produces high operating torques.

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Axial Piston Motor

Similar to piston pumps, axial piston motors work with a bent axis design or swash plate principle. The fixed displacement type works as a hydraulic motor, and the variable displacement type most often functions as a hydraulic pump. Fixed displacement motors may be used in both open and closed loop circuits.

In the bent axis design, pistons move up and down within the cylinder block bores. This motion is converted into rotary movement via the piston ball joint at the drive flange. In the swash plate design, pistons move up and down within the cylinder block and turn it, which then turns the drive shaft via the connected cotter pin.

Typical parameters of axial piston motors:

  • Displacement volume: 10 to 1,000 cc (multi-stroke up to 1,500 cc)
  • Maximum pressure: up to 450 bar
  • Speed range: 500 to 11,000 rpm
  • Maximum torque: up to 10,750 Nm

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Radial Piston Motor

Radial piston motors are used in caterpillar drives of dragline excavators, cranes, winches and ground drilling equipment. Radial piston motors are capable of producing high torques at very low speeds, down to half a revolution per minute. Therefore, radial piston motors are also referred to as Low Speed High Torque (LSHT) motors.

The pistons (or plungers) of a radial piston motor form a star-like shape and are perpendicularly connected to the shaft. The rectilinear motion of the pistons is transformed into a rotating movement by the eccentric shaft.

Typical parameters of radial piston motors:

  • Displacement volume: 10 to 8,500 cc
  • Maximum pressure: up to 300 bar (multi-stroke up to 450 bar)
  • Range of speeds: 0.5 to 2,000 rpm
  • Maximum torque: up to 32,000 Nm (multi-stroke up to 45,000 Nm)

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Part-turn Actuators

Part-turn actuators are mainly used for bunker slides, opening butterfly valves, and for push, pull, lift and mix operations.

This type of actuator, also known as a rotary actuator, can only rotate left or right over an angle of 300°. They operate at pressures around 70 bar. Part-turn actuators are much smaller than cylinders and do not have any external moving parts.

Part-turn actuators are very simple in design. There are two versions: one has two wings on the axle, and the other one has two internal dividers. This construction brings the swivel bracket back to around 120° and doubles the torque. The first version is prone to a low, continuous leakage rate along the wing. This means that, during operation, the rotary actuator must be under constant pressure in order to perform properly.

Part-turn actuators perform a slewing motion across a shaft end when pressurised with hydraulic fluid, regardless of the type or design of the unit. The angle that a part-turn actuator moves through is limited by fixed or adjustable stops. Due to this, the range of applications in which part-turn actuators may be used is limited.

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