Driving Heavy Equipment Efficiency with Hydraulic Steering Systems

How does a hydraulic steering unit work?

A steering control unit (SCU)—often called an orbitrol or hydrostatic steering unit—is a core component in many off-road and mobile machines like tractors, loaders, and forklifts. It enables smooth, precise, and low-effort steering by using hydraulic power instead of mechanical linkages.

The hydraulic steering control unit is composed of a rotary valve and a rotary meter. It connects to the vehicle’s steering wheel via a steering column. When the steering wheel is turned, hydraulic oil is directed from the system’s pump through the rotary valve and meter to either port L or R, depending on the direction of rotation.

The rotary meter delivers oil to the steering cylinder in proportion to the angular movement of the steering wheel, ensuring precise and responsive steering control.

What’s the difference between open-center and closed-center steering units?

The difference between open-center and closed-center steering units lies in how hydraulic fluid flows through the system when the steering is not being used, and how the hydraulic circuit is configured. These systems are common in hydrostatic steering used in tractors, construction equipment, and other off-road vehicles.

Comparison between Open Center or Closed Center Steering Units

Feature	Open-Center System	Closed-Center System
Flow at rest	Constant flow	No flow
Pump type	Fixed displacement	Variable displacement or load-sensing
Efficiency	Lower	Higher
Complexity	Simpler	More complex
Multi-function support	Limited	Excellent
Typical use	Basic equipment, lower cost	Advanced machinery, high-performance

Do hydraulic steering units require external power?

Hydraulic steering units do not require external electrical power to function — instead, they rely on hydraulic power, typically supplied by an engine-driven pump.

Power Source:

Powered by pressurized hydraulic fluid from a pump.
The pump is usually mechanically driven by the vehicle’s engine (via belt, gear, or shaft).

No External Electrical Power Required:

These systems are purely hydraulic.
The steering unit (orbitrol) directs fluid to steering cylinders based on the rotation of the steering wheel.
Manual fallback: Many designs offer limited manual steering if pump pressure is lost, using built-in mechanical reaction or hand-pump action from the orbitrol.

Can hydraulic steering units provide feedback to the steering wheel?

Hydraulic feedback is the reactive force felt by the operator due to pressure changes in the hydraulic circuit. It improves control, handling, and safety — but is not always present, depending on system design.

Steering Unit Type	Feedback to Steering Wheel?	Steering Feel	Self-Centering
No Reaction	❌ None	Disconnected	No (unless geometry forces it)
Reaction / Load-Reactive	✅ Yes	Natural feel	Yes (when load acts to center)

Rule of Thumb:

If your steering unit is labelled "Non-Reaction" or "No Reaction", it will not provide feedback.
If you want feedback, ask for a “reaction” or “load-reactive” steering unit.

Which steering unit is right for my machine?

Choosing the right steering unit for your machine depends on several key factors related to the machine's application, hydraulic system, and operating environment. Here’s a detailed breakdown to help guide your decision:

1. Machine Type and Application

Machine Type	Common Steering Unit Requirement
Tractors / Ag Vehicles	Load-sensing, reaction or non-reaction units
Forklifts / Telehandlers	Compact, low-displacement, often non-reaction
Construction Equipment	Robust, high-displacement, reaction units
Utility Vehicles / ATVs	Lightweight, responsive, usually non-reaction
Road Vehicles	Precision steering, often closed center with feedback

2. Hydraulic System Type - The steering unit must be compatible with your hydraulic setup.

Open Center: Constant flow; simple systems. Most commonly used in light and medium-duty machines.
Closed Center: Flow is on-demand; used in more sophisticated, load-sensing systems.
Load-Sensing: Efficient systems that adjust flow/pressure based on steering demand.

3. Reaction vs Non-Reaction - This refers to whether road surface feedback is transferred back to the steering wheel.

Reaction Units: Allow feedback from the wheels to the steering wheel, useful for operators who need road feel or manual override, Common in construction and road vehicles
Non-Reaction Units: Isolate the steering wheel from feedback, Prevents kickback or movement of the wheel when not turned by the operator, Ideal for off-road and agricultural use

4. Displacement (cc/rev)

This determines how much fluid is moved per turn of the steering wheel:

Low displacement: Faster steering, less torque
High displacement: Slower but more powerful steering

Choose based on how quickly and how much force your machine needs to turn the wheels.

5. Mounting and Port Configuration

Check mounting flange types (e.g., SAE, DIN)

Match port sizes and thread types (BSP, SAE, Metric)

Are hydraulic steering systems suitable for high-speed vehicles?

Hydraulic steering systems are not naturally suited to high-speed vehicles due to their lack of road feel, slower responsiveness, and potential safety risks. However, with advanced designs and fail-safes, they can be engineered to work in some high-speed specialty applications—but they're usually not the best choice for modern high-speed vehicles.

Hydraulic steering is commonly used in specialized vehicles such as military transports, heavy-duty trucks, airport fire engines, and off-road racing vehicles (e.g., rally trucks). In these applications, the systems are enhanced with features like reaction-type steering valves for improved driver feedback, closed-center load-sensing hydraulics to ensure responsive control, and redundant mechanisms such as backup pumps or mechanical overrides to maintain safety and reliability.

What information do I need to order a replacement steering unit?

To order a replacement steering unit, you'll need to gather specific technical and application details to ensure compatibility and proper performance. Below is a comprehensive checklist of the key information required:

Category	Details
Identification	Model, serial number, manufacturer
Specs	Displacement, reaction type, center type, porting
Mounting	Bolt pattern, flange, shaft type
Application	Machine model, usage environment
System Info	Pressure, flow, pump type

Do hydraulic steering units come with built-in load sensing or priority valves?

Yes, some hydraulic steering units do come with built-in load sensing and/or priority valves, especially in modern or OEM-focused systems. However, not all units include these, so it's essential to review the specific model details or system requirements before ordering or designing the hydraulic layout.