Driver Knowledge Tests

What is a hydraulic cylinder or ram on a truck?

Hydraulic cylinders or rams are used to move heavy parts of a truck, such as the:

  • Tipper bin
  • Sidelifter arms
  • Transporter ramps
  • Tail lift.
Telescopic hydraulic ram extended to lift up tipper bin
Hydraulic rams that control the lifting of the arms and the angle of the loader bucket

They are also used in earthmoving and civil construction machinery, for example:

  • Lifting arms or booms on a front-end loader or excavator
  • Articulated turning mechanism on a front-end loader
  • Lifting and extending the boom on a telehandler or truck loader crane
  • Stabilising outriggers on a crane or truck loader crane
  • Lifting the carriage on a forklift.
Hydraulic rams are used to take the weight of the crane on theses outrigger legs

The hydraulics are driven from the power take-off or PTO.

An example of a hydraulic cylinder. Image 2 shows where oil pressure flows into the cylinder to push out the ram. Image 1 shows that no fluid is being pushed into the ram.

The hydraulic system consists of a fluid reservoir with a pump. The pump pushes fluid (usually oil) into the base of the cylinder (shown in the diagram above as the red area) which extends the ram. The ram can extend by using sliding rings and seals, meaning the cylinder can fill from the bottom. Fluid from the top of the cylinder cycles back to the reservoir. A control valve determines where the fluid flows.

Tail lift operating controls change the flow of hydraulic fluid to the rams which lift and tilt the ramp

How should you check hydraulic rams in a pre-trip inspection?

  • Is the cylinder bent?
  • Does the cylinder have scratches or dents?
  • Are there any hydraulic fluid leaks from the shaft seals or fittings?
  • Is the hydraulic fluid low?

If you see any of those, then call your maintenance team to rectify it. When the cylinder is being maintained, it’s important to eliminate the risk of the machinery falling on someone or trapping limbs. For example, with a tipper bin, it should be suitably propped.

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

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