How does a hydraulic motor work?

How hydraulic motors work

Hydraulic motors are essentially mechanical actuators that work to convert fluid power into the mechanical energy needed to power a machine.
Fluid power is the driving force behind all hydraulic operations, including the way motors work.
Hydraulic motors use pressurised fluids from the hydraulic pump to generate force such as angular displacement and torque. As the fluid is carried to the hydraulic motor, it pushes on the gears, vanes or pistons of the motor and as a result, turns the motor output shaft.
The rotating shaft uses flow and hydraulic pressure to create rotation torque, therefore generating the power and force needed to move the external load. Then the cycle repeats.
The speed at which a hydraulic motor operates is dictated by the amount of oil and pressure supplied by the pump.

The different types of hydraulic motors

There are four main types of hydraulic motor, all with one or more sub-type. Each motor type has different characteristics, making one more suitable for certain applications than another.
The different types of hydraulic motors are characterised by their:

• Maximum operating pressure
• Maximum rotational speed
• Displacement (fixed or variable)
• Constant peak and power

Here are the most common types of hydraulic motors.

Gear Motors

The first type of hydraulic motor is the gear motor. There are two parts that make up a hydraulic gear motor. These parts are the idler gear and the driven gear. The output shaft is attached to the driven gear using a key. You port high-pressure oil into one of the gear’s sides, and then it flows between the wall housing and the gear tips into the outlet port. After that, the gears mesh, which prevents the oil in the outlet side from returning to the inlet side.

Low initial cost and greater tolerance to contamination are a few benefits of gear motors. Additionally, gear motors are generally quite durable, too. Fans, screw conveyors, and dispersion plates are a few common applications of hydraulic gear motors.

Vane motors

Vane motors are simple in design, consisting of a housing with an eccentric bore and a rotor with vanes. The pressurised fluid creates an unbalanced force on the vanes, which causes the rotor to spin in a single direction, either clockwise or counterclockwise.
Vane motors are small in size and particularly suited to vertical installations. They offer high torque at low speeds, stable operation, balanced flow, high input speed and low noise level.
Maximum pressure in vane motors can reach up to 230 bar, and they can deliver up to 650 Nm of torque with a displacement volume of up to 214cc.

Piston motors

Piston motors are available in two types; radial piston motors and axial piston motors.
Radial piston motors are low speed and high torque, capable of generating a far higher torque than axial piston motors. Here, the pistons are arranged perpendicular to the axis of the crankshaft and they move in a linear motion, which is then converted to rotary motion.
Axial piston motors generate a lower torque but have a higher speed range. In this type, the pistons are arranged in a circular pattern with housing that rotates about the axis by a shaft.

Hydraulic motors are rated by torque and displacement.

Displacement refers to the volume of fluid that the motor requires in order to rotate its shaft once. In any case, the ratings for the displacement of hydraulic motors are either cubic centimeters per revolution or cubic inches per revolution. In contrast, the common measurements for the torque of a hydraulic motor are Newton-meters and inch-pounds.

Differences Between Hydraulic Motors and Pumps

Understanding the differences between hydraulic pumps and motors is crucial. Although hydraulic pumps and motors operate in similar fashions, they have distinct characteristics that sometimes lead to confusion. People often interchange the terms pump and motor.

Some key distinctions between hydraulic motors and pumps include:

Hydraulic motors are designed to rotate in both directions. They possess internal symmetry to accommodate both positive and negative rotation, unlike hydraulic pumps, which generally rotate in a single direction.
For instance, a vane motor must have blades arranged radially and not inclined like a vane pump, as the latter would damage retracting blades. The distribution plate in the axial plunger motor is symmetrical, unlike the axial plunger pump.

Hydraulic pumps are predominantly connected to prime movers, whereas motors are linked with loads. Pumps typically don’t handle radial loads like those found in motors.
Hydraulic pumps operate with low-pressure vacuum creation which is not required for hydraulic motor functionality.
Hydraulic motors possess broad speed ranges and lubrication and bearing selection need to reflect this.
For hydraulic motors, the minimum stable speed is low, but other motors may only be effective with variable speeds and braking systems.
Hydraulic motors necessitate substantial startup torque to counteract friction.
Internal leakage occurs more in hydraulic motors than in comparable pumps.
Certain hydraulic motors can operate without slippers; whereas hydraulic pumps require them.