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A steering cylinder provides hydraulic power assist to the steering of a commercial vehicle, reducing the effort needed to turn heavy wheels. In linkage-assist systems a separate hydraulic cylinder acts on the steering linkage, while integral systems build the assist into the steering box.
Pressurised fluid from the power steering pump is directed by a control valve to one side of the cylinder piston as the driver turns the wheel. The piston pushes the steering linkage in the chosen direction, adding force to the driver's input. When the wheel is centred the valve returns to neutral. This assist lets a driver steer a heavily loaded truck with reasonable effort.
The cylinder seals can wear or leak, and because an external cylinder is exposed to road debris and impacts, its mountings and rod can be damaged. Signs include heavy or uneven steering, fluid leaks, a dropping reservoir level, and noise from the pump working harder. As a safety system, a leaking or weak cylinder should be inspected without delay, along with the fluid level and the rest of the power steering system.
The correct cylinder depends on the vehicle model, the steering system type, and the cylinder mounting and dimensions. Confirm the part against the vehicle specification before fitting.
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Frequently asked questions
What does a steering cylinder do?
It uses hydraulic pressure to add force to the driver's steering input, making it easier to turn the heavy wheels of a commercial vehicle.
What are the signs of a failing steering cylinder?
Heavy or uneven steering, fluid leaks, a dropping power steering fluid level, and the pump working harder. These should be checked promptly.
What is linkage-assist steering?
A design where a separate hydraulic cylinder provides power assist through the steering linkage, rather than the assist being built into the steering box. The external cylinder needs regular inspection.
Why does the power steering fluid level matter?
A dropping level usually means a leak, often at a cylinder or hose seal. Low fluid reduces assist and can damage the pump, so the leak should be fixed rather than just topped up.