The difference between single-acting and double-acting cylinders

Hydraulic cylinders are a key component of power hydraulic systems, converting the energy stored in compressed hydraulic oil into mechanical work. Depending on their design and mode of operation, there are two basic types: single-acting and double-acting cylinders.

How it works

Single-acting cylinders operate under hydraulic pressure in only one direction. Once the specified stroke is reached and the operation is complete, the piston rod retracts due to the force of the return spring or under its own weight. They have only one connection for the hydraulic oil supply.

Double-acting cylinders allow movement in two directions—both when the piston extends and when it retracts. They operate by using two hydraulic chambers filled with pressurized working fluid. When fluid flows into one chamber, the piston moves in one direction, and when pressure is directed to the other chamber, the piston returns in the opposite direction.

Design

Single-acting cylinders have a simpler design, which results in lower production costs. Their design includes a spring that returns the piston to its starting position at the end of the operating cycle.

Double-acting cylinders have a more complex design and do not include a piston return spring. Instead of a single chamber, they have two chambers, each with its own inlet, which allows hydraulic oil to be injected alternately from one side or the other of the piston.

Duty cycle

In a single-acting cylinder, the operating cycle proceeds as follows:

• Operating principle: High-pressure hydraulic oil is forced into the cylinder chamber, causing the piston to move and simultaneously compressing the return spring
• Piston return: Once the target is reached, the spring relaxes, causing the piston to retract and forcing the oil out of the chamber

In a double-acting cylinder, the operating cycle is as follows:

• Piston stroke: pressurized working fluid flows into the working chamber behind the piston, causing it to move in the direction of the stroke
• Piston return: the fluid flows into the opposite chamber, forcing the piston to move backward
• The oil is alternately forced into one chamber and then the other, applying equal force to the piston in both directions

Application

Single-acting cylinders are used in:

• Agricultural machinery: balers, spreaders, plows
• The construction industry: cranes and hoists
• Industrial equipment requiring precise piston movements in a single direction

Due to their versatility, double-acting cylinders are used in:

• Construction machinery: excavator and loader arms
• Industrial machinery: lifting, moving, and rotating systems
• Agricultural machinery: agricultural balers and tractor hydraulic systems
• Automation and robotics: precision control systems

The selection of the appropriate type of hydraulic cylinder depends on the specific application, the requirements for motion precision, and the cost-effectiveness of the hydraulic system.