Orbital Hydraulic Motors: Principle, Structure, Applications & Maintenance | Blince

Do You Really Understand Your Hydraulic Motor?
When is an orbital hydraulic motor the right choice for your machine?

Have you ever wondered how the motor that powers your equipment every day actually works? How does an orbital motor differ from a gear motor or piston motor?
Or maybe you’re unsure whether your system even needs an orbital motor. Choosing the wrong motor not only wastes time and money—it can also damage your equipment. Let’s clear things up.

What Is an Orbital Hydraulic Motor?

To begin, let’s clarify what an orbital hydraulic motor is.
An orbital motors is a compact, high-performance low-speed high-torque (LSHT) hydraulic actuator. Its core design features a special gear mechanism known as a gerotor set or orbital gear set, which enables it to deliver large torque at low speeds with a significantly smaller size compared to other motor types. This results in high power density.

Orbital motors offer a wide speed range and smooth, stepless control. Their stable minimum operating speed can be as low as 15 RPM, making them ideal for precision low-speed applications.
They have a simple yet robust structure and can be directly connected to the load (e.g., wheels or drums), eliminating the need for a gearbox and reducing the cost and complexity of the hydraulic system.

Thanks to their excellent startup performance and efficiency, orbital motors are widely used in construction equipment (e.g., excavator travel drives), agricultural machinery, port systems, and industrial automation—whether in series or parallel hydraulic configurations.

Structure of an Orbital Hydraulic Motor

The heart of an orbital motor is its unique orbital gear mechanism.
Inside the housing is a stator with needle teeth (or rollers), which is either machined directly or installed as a separate component. Pressurized oil enters the motor and acts on a rotor with a cycloidal (orbital) profile, causing it to perform eccentric planetary rolling motion within the stator.

This motion is transmitted directly through a rigidly connected spline output shaft, converting hydraulic energy into mechanical torque.
The precise meshing between the rotor and the needle teeth on the stator is key to transmitting high torque. This design reduces sliding friction (mainly converting it into rolling friction), which greatly enhances mechanical efficiency and delivers strong startup torque and excellent low-speed stability—even at extremely low speeds.

By reversing the inlet and outlet ports, the motor achieves instant bidirectional rotation with nearly equal torque in both directions.
Each motor series offers various displacements (by changing rotor/stator geometry) to meet diverse speed and torque requirements.

Why Trust This Article? We Have a Professional Engineering Team

Hello, I'm hydraulic engineer Amy. Customers often ask, “Why should I trust Blince hydraulic advice?”
The answer is simple: because we build and service motors every single day.

At Blince, this isn’t just talk. Every engineer is hands-on with production and deeply familiar with each motor model.
So, when you consult us, we don’t just give a "yes" or "no" answer—we provide advice based on three key pillars:

• Thousands of hours of practical experience – Is the motor suitable for your working conditions?

• Application-specific understanding – How will it perform in your machinery?

• Budget-fit optimization – How to balance performance and cost to find the best solution.

How an Orbital Hydraulic Motor Works

The core principle of an Cycloidal Hydraulic Motors is planetary gear motion between the rotor and stator.
The stator features needle rollers or pins, and the rotor has an orbital (cycloidal) profile. With a one-tooth difference between the two, multiple sealed chambers are formed.

Pressurized oil is precisely routed via a distribution system (such as a disc or shaft distributor) into the dynamically changing sealed chambers formed between the rotor, stator, and end caps.
Due to the fixed eccentric offset between rotor and stator centers, the rotor experiences compound motion: rotation around its own axis and planetary revolution around the stator.

This eccentric orbital motion is directly converted into low-speed, high-torque output via the splined output shaft.
The distributor ensures that high-pressure oil always acts on the torque-generating side of the rotor to maintain continuous rotation.

This working principle enables excellent low-speed smoothness and high starting torque.
Reversing the oil flow direction allows immediate change in rotation direction with nearly equal torque output in both.
Some designs include internal case-drain passages for pressure balancing, cooling, and extended seal life.

It is this efficient and reliable principle that makes orbital motors a popular choice in agriculture, construction, lifting, and rotating systems.

Operating Tips for Orbital Hydraulic Motors

1. Before starting, ensure all components are correctly connected and fill the tank to the specified level using filtered oil.

2. After startup, let the system run at no-load for 10–15 minutes to purge air. Foam in the tank, abnormal noise, or jerky motor behavior indicates trapped air.

3. Once air is removed, top up the oil and gradually increase motor load to maximum. Watch for abnormalities such as noise, rising oil level, or leaks.

4. After 50 hours, change the hydraulic oil and follow scheduled maintenance intervals.

5. Do not disassemble the Cycloidal Hydraulic Motors unless a clear internal fault is identified.

Maintenance Essentials for Orbital Motors

Consistent maintenance is crucial for ensuring long  orbital motor life. Focus on:

Hydraulic Oil Management

• Monitor oil condition: check viscosity, cleanliness (ISO 4406), and contamination level; replace degraded oil and filters in time.

• System flushing: after major repairs or component replacements, flush the circuit thoroughly to remove contaminants.

Leakage & Seal Inspection

• Shaft seals are prone to leakage: check for oil residue and replace seals immediately if seepage is found.

• Inspect housing seals and port fittings to prevent fluid loss or contamination.

Mechanical Health Monitoring

• Listen for abnormal noise: could indicate worn bearings or rotor/stator damage.

• Check output shaft runout: excessive movement signals bearing failure or rotor deformation.

• Periodically inspect the rotor and stator for wear; replace if significant scoring is found.

Case Drain Line Maintenance

• Ensure case drain lines (if equipped) are unobstructed. Blockages increase back pressure and cause seal failure.

• Case drain must return directly to the tank without pressure to avoid seal damage.

Applications of Blince Orbital Hydraulic Motors

Below are real-world examples of Blince orbital motors in action:

• Concrete placing machines: OMSY-125 and OMSY-80

• Mini excavators: OMR-200 (2 for travel, 1 for swing)

• Hydraulic attachments: OMT-630, OMSY-475, OMR-250 used in shears, crushers, tampers, drills, breakers, grapples, log grabs, clamshell grabs, pile drivers, vibratory tampers

• Rotary shears: OMT-500

• Snow plows: OMSY series

• Rotating clamps: OMSY-200

• Road maintenance trucks: OMR160 for asphalt conveyor, OMSY-400 for asphalt mixer

Blince – Your Trusted Orbital Motor Specialist

Blince Hydraulic brings over 20 years of industry experience.
We operate modern manufacturing lines, robust R&D programs, and precise testing systems.
We are ISO 9001 and CE certified and hold 10 registered patents in hydraulic motor technologies.

Learn more at our official website: www.blince.com