Hydraulic motors are a good choice in many applications, but a cursory search reveals there are several types to choose from. This blog will explain the advantages of orbital motors over the other designs, identify where they should be used and where other designs might be more appropriate.

Why Use Hydraulic Rather Than Electric Motors?

Just as a generator can function as an electric motor, a hydraulic pump can also become a motor, turning fluid flow into rotary motion. Hydraulic motors are ideal where it’s impractical to provide enough current and voltage for an electric motor to make the torque and power required.

Mobile machinery is an important application area, but these motors also drive heavy-duty industrial equipment like long conveyors, mixers and molding machines. A particular niche is in environments where there’s an explosion risk: avoiding the use of electricity eliminates a potential source of ignition.

Types of Hydraulic Motor

The main methods of turning fluid flow into rotary motion are:

• Pistons
• Vanes
• Gears

There are various designs of hydraulic piston motor. All use the principle of fluid pushing on a piston that in turn acts on a shaft, or in some cases, a swash plate connected to a shaft.

Vane motors might be considered similar to an old style waterwheel. Vanes are arranged around the periphery of a wheel with their outer edge sealing against the housing. Fluid enters through an inlet port and pushes against the vanes to make the wheel turn.

Gear motors split into two types: external gears, similar to a spur gear oil pump, and gerotor designs that have a gear within a gear.

In a gerotor the inner gear rolls around the surface of the stationary outer gear. Fluid pressure turns the inner gear, which performs an orbit inside the stator, hence the name hydraulic orbital motor. An output shaft connected to the rotor delivers the motion and torque.

Key Characteristics of Hydraulic Orbital Motors

In this design the inner gear or rotor has one tooth less than the outer stator. This creates a gear ratio where the orbit speed is far lower than the rate at which the rotor rolls around the stator. This speed reduction has the effect of multiplying torque, so a hydraulic orbital motor produces high torque at low speed.

A second noteworthy feature is size. Placing the rotor inside the stator creates a compact design, resulting in higher power density, (a measure of torque produced for volume of motor), than other types of hydraulic motor.

Advantages of Hydraulic Orbital Motors

A combination of factors make these motors the best choice for a long list of applications:

• Higher power density than other designs
• High torque
• Low output speed
• Less complex than piston motors
• More durable than vane motors

Limitations

Despite their versatility and utility, there are situations where a hydraulic orbital may not be the best choice. For example,

• If an application requires high speed – greater than 500-1,000 rpm – a hydraulic orbital motor would probably need some form of speed-multiplying transmission, adding cost and complexity
• In low torque applications running a hydraulic orbital motor far below its rated output will extend its life but other designs may be more cost-effective

Good Applications for Hydraulic Orbital Motors

Their high power density makes these the preferred choice for wheel motors in equipment like skid steers. They are also used extensively in mobile machinery used in agriculture, forestry, construction and mining.

In stationary industrial applications space and motor size are of less importance than performance, durability and cost. When low speed is needed, a hydraulic orbital motor can avoid the need for a speed-reducing transmission. The rugged, robust design is also good for reliability and longevity.

The Right Hydraulic Motor for Your Application

Impro Fluidtek manufactures three families of hydraulic orbital motor for light, medium and heavy-duty applications. Displacements, speeds and torque depend on the specifics of each design, but all provide the high power density and torque along with low speed that makes them the first choice in many applications. Contact us to discuss your application and learn more.