New Arrival Double Acting Dump Truck Telescopic Hydraulic Cylinder For Sale

1. Directional Control Valve

Double-acting requires a 4-way, 3-position (4/3) directional control valve. The three positions are: extend (pressure to extend port, return from retract port), retract (pressure to retract port, return from extend port), and neutral (both ports blocked or floating). Single-acting uses a simpler 3-way valve. If your truck currently has a 3-way valve and you are upgrading to a double-acting cylinder, the valve must be replaced or a second valve section added.

2. Hydraulic Pump

The pump must deliver sufficient flow (litres per minute) at adequate pressure (bar or PSI) to extend the cylinder at the desired tipping speed. Flow determines speed; pressure determines force. A larger bore cylinder requires more flow to extend at the same speed as a smaller bore. The pump pressure rating must exceed the system working pressure by a margin — typically the pump relief valve is set 10–15% above the cylinder's rated working pressure to ensure the cylinder operates at full force.

3. Hydraulic Hoses

Double-acting requires two hose lines — one for extend, one for retract. The hose internal diameter must be large enough to carry the pump flow without excessive pressure drop. Undersized hoses create friction losses that reduce the effective pressure at the cylinder — the dump body rises more slowly and with less force than the pump output should provide. The hose pressure rating must match or exceed the system relief valve setting. Both hoses must be correctly routed to avoid chafing, kinking, or contact with hot exhaust components.

4. Hydraulic Reservoir

The reservoir must hold enough hydraulic fluid to fill the cylinder at full extension plus maintain a minimum level above the pump suction port. A telescopic cylinder displaces a significant oil volume — a 4-inch bore, 4-stage cylinder at 80-inch stroke displaces approximately 6–8 litres. The reservoir must accommodate this volume swing without running dry on the extend stroke or overflowing on the retract stroke. Undersized reservoirs cause pump cavitation (air ingestion) on the extend stroke and fluid overheating due to insufficient cooling time.

Extension speed = Flow ÷ Bore area

The extension speed of each stage equals the pump flow rate divided by the piston area of that stage. A larger bore has a larger piston area, so it extends more slowly at the same flow rate. The first stage (largest bore) extends the slowest; the last stage (smallest bore) extends the fastest. If the tipping speed is too slow, either increase the pump flow or reduce the bore (which also reduces force — a trade-off).

Retract speed = Flow ÷ Annular area

On the retract stroke, the flow fills the annular area (bore area minus rod area), which is smaller than the full bore area. This means the retract speed is faster than the extend speed at the same flow rate. On a dump truck, this translates to the body lowering faster than it rises — which is usually acceptable, but if the lowering speed must be controlled, a flow control valve on the retract circuit provides metering.

Closed centre — body holds position

When the valve returns to centre, both cylinder ports are blocked — hydraulic fluid is trapped in both the extend and retract chambers. The dump body holds its current tipping angle. This is the standard choice for dump trucks where the driver needs to stop the body at a partial tipping angle (for metered discharge or inspection). The body will not move until the driver actively selects extend or retract.

Float centre — body free-falls under gravity

When the valve returns to centre, both ports are connected to the return line — fluid flows freely in and out of the cylinder. The dump body is free to move under gravity, which means it will lower by itself if it is above horizontal. Float centre is used when the driver wants the body to automatically lower to horizontal when the lever is released. This is convenient for rapid cycle operations but provides no holding capability — the body cannot be stopped at a partial angle.

My dump truck tips too slowly — is the cylinder undersized or the pump?

Usually the pump. The cylinder's bore determines force, not speed. Speed is determined by how fast the pump fills the cylinder bore area. If the tipping speed is unacceptable, check the pump flow rate first — it may be insufficient for the cylinder bore. Also check for restrictions in the hose lines, filter, and control valve that reduce the effective flow reaching the cylinder. A partially clogged filter or an undersized valve can reduce tipping speed by 30–50%.

What hose size do I need for a 4-inch bore double-acting telescopic cylinder?

Hose size depends on the pump flow rate, not just the cylinder bore. As a general guideline, the hose internal diameter should maintain a fluid velocity below approximately 6 metres/second for pressure lines and 3 metres/second for return lines. At 20 litres/minute, a 1/2-inch (12.7 mm ID) hose maintains approximately 2.6 m/s — well within limits. At 40 litres/minute, a 3/4-inch hose is appropriate. Always confirm with a hydraulic hose sizing calculation or consult your hose supplier.

How large should the hydraulic reservoir be?

The reservoir must hold the full cylinder displacement volume plus a minimum operating reserve above the pump suction port. A common guideline for mobile hydraulic systems is that the reservoir capacity should be at least 2–3 times the pump flow rate per minute (for cooling) plus the cylinder displacement volume. For a dump truck with a 4-inch bore, 4-stage, 80-inch stroke cylinder displacing approximately 6–8 litres, and a 20 L/min pump, a 50–60 litre reservoir is typical.

Can Korea Ever-Power supply the valve, pump, and hoses as well as the cylinder?

Korea Ever-Power's core manufacturing capability is hydraulic cylinders — including telescopic, welded, and tie-rod types for forklifts, aerial work vehicles, and dump trucks. The factory can recommend compatible valve, pump, and hose specifications for your system, but these components are typically sourced from their respective specialist manufacturers. The engineering team will provide the flow, pressure, and port specifications needed so you can order the supporting components from your preferred hydraulic component supplier.

We design complete dump truck hydraulic systems — cylinder, valve, pump, reservoir, hoses, and controls. The Ever-Power engineering team provided the cylinder displacement data and port flow coefficients that we needed to model the circuit before ordering. This system-level technical support is rare from cylinder suppliers — most just provide bore and stroke. The double-acting 4-stage, 5-inch bore we ordered matched the circuit model precisely: the tipping speed on site was within 5% of our calculated prediction. 8 complete systems installed, all performing to specification.

Upgraded 3 dump trucks from single-acting to double-acting. The cylinder replacement was straightforward, but I underestimated the system changes needed: had to replace the 3-way valves with 4-way, add retract hose lines, and enlarge the reservoir on one truck that was running marginal oil capacity. Four stars because the total conversion cost was about 40% more than the cylinder price alone — the system components added up. The system integration guidance on this page would have helped me budget the complete conversion more accurately. The cylinders themselves are excellent — smooth bi-directional operation on all 3 trucks.

We specified closed-centre valves on our municipal dump trucks following the safety guidance — personnel occasionally work adjacent to raised dump bodies during salt loading in winter. The closed centre hydraulic lock holds the body securely at any angle. The Ever-Power double-acting cylinder paired with a Bosch-Rexroth 4/3 closed-centre valve provides exactly the behaviour we need: body stays where the operator puts it, no drift, no unintended lowering. The system integration information helped our specification engineer select the correct valve centre position before ordering.