Truck Hydraulic Parts Dammam

The components in a truck hydraulic circuit

• Power take-off: a drive from the gearbox or the engine that turns the hydraulic pump, with its own engagement control.
• Pump: usually a gear pump on tipper circuits, with piston pumps on higher-pressure crane and mixer systems.
• Control valve and lever, which direct the flow to the hoist or the crane functions.
• Cylinders: telescopic hoist cylinders on tippers, and double-acting cylinders on cranes and tail-lifts.
• Hoses, rigid pipes and fittings.
• Tank, breather, suction strainer and return filter.
• Seals, wiper rings and O-rings.

Tippers, cranes, mixers and tail-lifts: how the circuits differ

A tipper hoist is the simplest circuit: a pump delivers oil to a single-acting telescopic cylinder through a control valve, and gravity lowers the body. Crane circuits use double-acting cylinders with holding valves that stop the load from dropping if a hose fails, plus outriggers with cylinders of their own. Concrete mixers usually turn the drum with a hydrostatic drive, a variable-displacement pump feeding a hydraulic motor. Tail-lifts use a compact electro-hydraulic power pack that runs from the truck's 24-volt supply.

Construction chassis such as the Mercedes-Benz Arocs, Volvo FMX, MAN TGS and Sinotruk HOWO tippers are typically ordered with the power take-off prepared, but the pump, valve and cylinder normally come from the body builder. That makes the body maker's data plate as important as the truck's chassis number when you order.

Identifying a hydraulic part: what to measure

Replacing a hose: a safe sequence

1. Park on level ground, lower the body or support it mechanically, switch off the engine and disengage the power take-off.
2. Release the residual pressure by operating the control lever with the engine off, and loosen the fitting slowly.
3. Cap the open ports and hose ends at once to keep dirt out of the system.
4. Match the new hose to the old one for length, pressure rating and both end fittings, and check thread types with a gauge instead of by eye.
5. Route the hose so that it cannot kink, rub or touch hot parts, and use the original clamps and sleeves.
6. Refill and bleed the system, operate each function slowly and look for leaks with a piece of cardboard, never with your hand.

Why heat and dirt decide hydraulic life here

Hydraulic oil must keep the right viscosity at its real operating temperature. A tipper working through a Dammam summer can push tank oil temperatures far above the figures in a brochure. The oil thins, pumps slip and wear, and rubber seals harden. Choose an oil that stays within the pump maker's viscosity range at the temperature the system reaches, keep the tank breather clean and check the oil cooler where one is fitted.

Dirt is the second problem. Sand on a chrome cylinder rod is dragged past the wiper seal on every retraction and scores the rod, and the scored rod then cuts the seal. Keep rods wiped clean and wiper rings in good order. Mixers and crane trucks working Dammam's industrial sites, site tippers and trucks on dusty farm roads all work in exactly the conditions that punish rods and breathers.

Filters, strainers and breathers: the cheapest protection

Most hydraulic failures start with dirty oil. The suction strainer keeps large debris out of the pump, the return-line filter catches wear particles and often carries a clogging indicator, and the tank breather stops dust entering as the oil level rises and falls. Change the filter element on schedule, replace a breather that is clogged or cracked, and after any pump or cylinder failure flush the system, because debris from the failed part will destroy its replacement. An oil sample can show you the contamination level before a component fails.

Reading the symptoms: pump, cylinder or valve?

• Slow or weak lifting with a normal oil level: a worn pump with internal leakage, or a relief valve stuck open.
• The body creeps down under load: leaking cylinder seals or a leaking control valve.
• A noisy pump with foamy oil: air entering the suction line, which causes cavitation.
• Jerky movement: air in the system or a worn valve spool.
• Oil weeping from a cylinder gland: a worn rod seal or a scored rod.

Reseal the cylinder or replace it?

A seal kit can bring a cylinder back to life when the rod and barrel are undamaged. A scored rod or barrel usually means a new cylinder, or a rod that has been re-chromed to the right size. Telescopic hoist cylinders are long, with several stages, so a replacement has to match the stroke, the mounting style and the port positions exactly. Send us the cylinder's data plate and a photograph of both ends.

Ordering hydraulic parts

Send the chassis number and the body or crane maker if you know it, photographs of the part in place, any numbers on its data plate and the measurements from the table above. Photographs of hose ends and fittings help us match thread types, which are often the difference between a fitting that seals and one that leaks or strips.

Hydraulic questions from tipper and crane operators