Double-Acting Cylinder
A double-acting cylinder is a cylinder with two ports that works with pressure in both the push and pull directions. The directional control valve selects which port to pressurize, and the opposite port drains to tank. It is the standard actuator of mobile crane booms, buckets and tipper mechanisms.
Being able to produce controlled force in both directions means you do not have to rely on the weight of the load. However the two directions are not symmetric: the area on the rod side is smaller by the cross section of the rod. On an 80/45 mm cylinder the piston side is about 50.3 cm² and the rod side about 34.4 cm². This means that at the same pressure the pull force drops to about 68%, while in return the pull speed increases about 1.5 times.
- Practical consequence: at the same joystick opening the lowering and lifting speeds feel different; this is not a setting error.
- Air bleeding: after installation, air is expelled by making a few full strokes in both directions.
In electronic lever control, knowing this asymmetry lets you interpret "one direction is faster" correctly after calibration. On HCT kits the directions are taught separately; the source of the perceived speed difference is usually not the kit but the geometry of the cylinder.
Where this term is used: What Is a Hydraulic Lever Retrofit Kit? Definition, Components, Operating Principle