Single-Acting Cylinder
A single-acting cylinder pushes with pressure in one direction only; its return is provided by the load's own weight or by a spring. Because it has a single port, hose and valve requirements are reduced. It is used on dump bodies, lifting platforms, and some tractor lift circuits.
The price of this simple construction is that lowering is controlled not by pressure but by the orifice in the tank line. To limit lowering speed, a throttle valve or an adjustable lowering valve is placed in the line. If the load is light, lowering slows; if heavy, it speeds up; this behavior comes from the nature of the cylinder.
- Spring return type: for short stroke, low force applications; the spring consumes part of the usable force.
- Gravity return type: more common on mobile equipment; with no load the cylinder does not retract.
- Bleeding: because there is a single port, air bleeding is harder, so a bleed screw is placed at the highest point.
In such a circuit, electronic lever control gives a fully proportional feel in the lifting direction, while in the lowering direction the felt speed remains load dependent. Expectations must be set accordingly: the remote control manages the lever's position, not gravity.
Where this term is used: What Is a Hydraulic Lever Retrofit Kit? Definition, Components, Operating Principle