What Is a Double Acting Hydraulic Cylinder?

by | Jul 23, 2026 | single acting cylinder


A double acting hydraulic cylinder is a linear actuator that produces hydraulic force in both extension and retraction directions. Unlike a single acting hydraulic cylinder — which relies on gravity or a spring to retract — a double acting hydraulic cylinder uses hydraulic pressure for both strokes. It has two ports: pressurising the cap-end port extends the rod; pressurising the rod-end port retracts it. The double acting hydraulic cylinder is the dominant actuator type in excavators, loaders, steering systems, and any application requiring controlled force in both directions of travel.

Double acting hydraulic cylinder factory supply direct both port connections

How a Double Acting Hydraulic Cylinder Works

A double acting hydraulic cylinder operates through a four-way directional control valve that routes pressurised oil to either the cap-end or rod-end port while simultaneously connecting the opposite port to the tank return line. On the extension stroke, oil under system pressure enters the cap-end port and acts on the full piston face area (bore area = π × r²), generating the extension force. The rod-end oil is displaced through the rod-end port back to the reservoir. On the retraction stroke, the valve reverses: oil enters the rod-end port and acts on the annular area between the bore and rod (annular area = bore area minus rod area), generating the retraction force. The cap-end oil returns to reservoir. In neutral, both ports are blocked and the cylinder holds its position.

Extension Force vs Retraction Force: Why They Differ

The extension force of a double acting hydraulic cylinder is always greater than its retraction force at the same system pressure. This is because extension uses the full bore area, while retraction uses the smaller annular area — the bore area minus the rod cross-sectional area. The ratio of extension to retraction force equals the ratio of bore area to annular area.

Extension Force = Pressure × π × (Bore/2)²
Retraction Force = Pressure × (π × (Bore/2)² − π × (Rod/2)²)

Example: 100 mm bore / 56 mm rod at 20 MPa:
Extension = 20M × 0.007854 = 157.1 kN
Retraction = 20M × 0.005391 = 107.8 kN
Retraction is 31% less force than extension at the same pressure.

This force asymmetry must be considered when sizing the cylinder for applications where retraction force is critical — for example, a bucket curl cylinder on a loader that must curl against a full bucket under both extension and retraction. If the retraction force is insufficient, either the system pressure must be increased on the retraction stroke, or a larger bore cylinder must be specified.

Welded double acting hydraulic cylinder cross tube showing both port circuit

Double Acting vs Single Acting: When Each Is the Right Choice

Criterion Double Acting Single Acting
Hydraulic lines required 2 — cap end and rod end 1 — cap end only
Control valve type 4/3 directional control valve 3/2 or simple 4/3
Retraction mechanism Hydraulic pressure Gravity, spring, or load
Force on retraction Full hydraulic — adjustable Limited by spring rate or load weight
Horizontal mounting Fully supported Spring return needed
Position holding Both ports blocked in neutral Cap-end only; POCV needed for load holding
Circuit cost Higher — two lines, complex valve Lower — one line, simpler valve
Best applications Excavators, loaders, steering, two-way presses Lifting, clamping, tipping, log splitting

Key Applications of Double Acting Hydraulic Cylinders

Excavator and Construction Equipment

Boom, arm, and bucket cylinders all require full hydraulic force in both directions — to lift and lower under load, and to curl and dump against material resistance. Double acting is the only practical solution.

Agricultural Loader Booms

Telehandler and front loader boom cylinders must extend to lift loads and retract to lower them while carrying a full bucket. The retraction force must handle the bucket weight plus any resistance from compacted material.

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Steering Cylinders

Hydraulic steering requires full force in both left and right directions at any vehicle speed and load. Double acting cylinders in both directions of the steering rack provide consistent steering effort regardless of road surface.

Horizontal Industrial Presses

Where gravity cannot assist return, double acting cylinders provide controlled force in both the pressing and return directions, with adjustable speed and force on each stroke through flow and pressure control.

Double acting hydraulic cylinders from Ever-Power are available in welded and tie rod configurations, bore sizes from 32 mm to 250 mm, stroke lengths from 50 mm to 3,000 mm, and working pressure ratings to 31.5 MPa. Custom specifications including non-standard bore-stroke combinations, special seal compounds, and stainless steel construction are available with prototype quantities from one unit. Contact the engineering team with your application requirements for a specification and price.

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Frequently Asked Questions

1. What is a double acting hydraulic cylinder?+
A double acting hydraulic cylinder is a linear actuator that uses hydraulic pressure to produce controlled force in both the extension and retraction directions. It has two hydraulic ports — one at the cap end (driving extension) and one at the rod end (driving retraction). A directional control valve routes pressurised oil to whichever port is required, while the opposite port returns oil to the reservoir. This bidirectional hydraulic control makes the double acting hydraulic cylinder the most versatile actuator in industrial and mobile machinery.
2. What is the difference between single acting and double acting hydraulic cylinders?+
A single acting hydraulic cylinder uses hydraulic pressure in one direction only — extension — and relies on gravity, a spring, or the load for retraction. A double acting hydraulic cylinder uses hydraulic pressure in both directions, providing full controlled force on extension and retraction. Single acting needs one hydraulic line and a simpler valve; double acting needs two lines and a 4-way directional valve. Double acting provides better position control and suits applications with loads in both directions.
3. How does a double acting hydraulic cylinder work?+
When the directional control valve shifts to the extend position, pressurised oil enters the cap-end port and acts on the full piston face area, pushing the rod outward. The rod-end oil is displaced back to reservoir through the rod-end port. When the valve shifts to retract, pressurised oil enters the rod-end port and acts on the annular area between the bore and rod, pushing the piston inward. The cap-end oil returns to reservoir. Shifting to neutral blocks both ports, holding the cylinder in position.
4. What are double acting hydraulic cylinders used for?+
Double acting hydraulic cylinders are used wherever force is required in both extension and retraction directions: excavator booms, arms, and buckets; loader and telehandler booms; steering cylinders on agricultural and construction machinery; horizontal actuators where gravity cannot assist retraction; precision positioning systems requiring controlled movement in both directions; and any application where the retraction load is variable or may exceed the available return force from gravity or a spring.
5. Is a double acting cylinder better than single acting?+
Not universally — the better choice depends entirely on the application. A double acting hydraulic cylinder is necessary when controlled hydraulic force is required on retraction, when mounting orientation prevents gravity-assisted return, or when the load may act in either direction during the work cycle. A single acting cylinder is simpler, less expensive, and perfectly adequate for any lifting, clamping, or pressing application where gravity or a spring provides reliable retraction. Over-specifying a double acting cylinder where single acting is sufficient adds cost and complexity without benefit.