Agricultural, construction and landscaping machinery use hydraulic orbital motors because they’re rugged and durable. When sized correctly for the application and maintained correctly, they will provide years of trouble-free service. However, on rare occasions, issues can arise. This blog identifies the most common problems and offers advice on how to resolve them.

Hydraulic Orbital Motor Basics

An appreciation of how these motors work is key to understanding what can go wrong. Here’s a short introduction.

Hydraulic motors generate rotation from a flow of incompressible oil. These motors come in various forms, but the orbital design is strongly preferred for applications needing high torque at low speed from a compact package.

Hydraulic orbital motors use a gerotor design. This is where a gear with large lobes rather than teeth, (the ‘rotor’), sits inside an outer stator gear. The rotor has one less teeth than the stator and can roll around its surface. As it rolls, contact between lobes and stator teeth divides the open volume within the stator into two parts.

Fluid is pumped under pressure into one of these parts, which pushes the rotor towards the lower pressure side. A manifold on the input side moves the fluid input around as the rotor rotates. This generates rotary motion, which is sent out via a shaft connected to the inside of the rotor.

Common Problems

The main problems users experience are fluctuations in output speed, low power and oil leaks.

Output speed variation, along with low power, (which may mean low torque, low speed, or a combination of the two), signifies fluid flow problems or wear between rotor and stator. Wear lets fluid past the teeth, from high to low pressure regions, which reduces the torque generated.

Oil leaks occur as ‘O’ rings in the assembly fail. This is a natural result of aging, with the rubber gradually taking a compression set. High loads, impact loads and running hot can all contribute to accelerated ‘O’ ring wear.

Fixing Common Hydraulic Orbital Motor Problems

The sooner problems are found, the easier they are to fix. For this reason, we strongly encourage regular inspections and routine maintenance.

Speed and torque problems will usually be reported by equipment operators. When this happens:

• Check fluid delivery – are the flow rate and pressure where they should be?
  • If not, look for blocked filters or a low fluid level
  • Using fluid of the wrong viscosity can cause problems such as cavitation inside the motor
• If fluid flow is correct, there may be leakage from high to low pressure regions inside the stator. This could signify worn bearings or worn rotor and stator teeth. In either case, a rebuild is required.

Oil leaks will be visible on the exterior of the motor housing. These could be from:

• Loose hydraulic hose couplings – a result of vibration or thermal cycling – tighten as needed
• Failed ‘O’ rings – remove motor from service – disassemble and replace

Durable Motors for High Torque at Low Speed

Problems with hydraulic orbital motors are uncommon, provided the motor was sized correctly for the application and receives periodic maintenance. However, when they do occur, it may be that the motor is not to blame. Except in the case of oil leaks, start troubleshooting by looking at the system supplying the hydraulic fluid. Problems here will result in the motor not running as expected.

Unfortunately, as with all mechanical devices, the internal components of these motors will wear, and eventually rebuilding or replacement will be needed. However, when used within normal operating parameters it should take many years to reach this point.

Impro Fluidtek produces a range of rugged and compact hydraulic motors. Engineered for applications in mobile equipment, industrial machinery, and material handling, these deliver high torque at low speed while requiring minimal maintenance. Contact us to learn more.