The hydraulic cylinder is the workhorse of the industrial world. Read about the advantages and disadvantages of single and double-acting hydraulic cylinders.
In a previous article, we discussed the different types of hydraulic cylinders. We briefly touched on single-acting and double-acting cylinders. This article explains how to differentiate between these two cylinder types. The function you want your cylinder to perform determines if you should use a single-acting or a double-acting hydraulic cylinder.
Single-acting hydraulic cylinder
Singe-acting cylinders create force in only one direction, be that a push or pull action. These cylinders are also known as “plunger” cylinders. They are used in lifting applications where pressure from the hydraulic pump extends the hydraulic cylinder and a mass or a spring retracts it. Single-acting cylinders have only one port where the pressurised oil from the hydraulic pump flows in. This extends the piston in one direction which compresses the spring attached to the piston. The spring or the attached mass will retract the piston rod after releasing the air back through the cylinder port where it entered.
There are two different types of single-acting cylinders: the push and pull-type cylinders. As the names suggest, the push-type will allow the air entering to push the piston out of the cylinder. The pull-type allows the oil entering the hydraulic cylinder to pull the piston inside the cylinder. Single-acting cylinders are ideal for one-way linear movement. They are used in hydraulic jacks and forklifts.
Advantages of single-acting cylinders
- They are inexpensive to produce which means it will not break the bank to purchase one
- Their design is very simple which means less maintenance
- They use fewer seals than a double-acting cylinder
- Since there is only one port, you will save money on valve and piping costs
Disadvantages of single-acting cylinders
- There is a reduction in the thrust generated by the cylinder due to the opposing force of the spring.
- The spring wears after a while, making the strokes of the hydraulic cylinder inconsistent at that time.
Double-acting hydraulic cylinders
Double-acting hydraulic cylinders have pressure flowing from two ports. One of the ports is where the “advance” hydraulic hose fitting connects to. The hydraulic power of the pump causes the cylinder to extend through that first port. Attached to the second port is the “retract” hydraulic hose fitting. The double-acting hydraulic cylinder uses hydraulic power to extend and retract the cylinder. Force is generated in both directions, unlike the single-acting cylinder that produces force in only one direction. This gives the cylinder the ability to both push and pull.
Pressurised fluid alternates between both sides of the piston, creating the push and pull forces that move the piston rod. The application in which these hydraulic cylinders are installed has more control over its movement. Different levels of movement are achieved by using 2-, 3-, or 4-way position valves. Double-acting hydraulic cylinders are used in mobile applications like the boom of a TLB or to control the steering in an excavator.
Advantages of double-acting cylinders
- They can apply pressure in two directions
- They are stronger and faster than single-acting cylinders
- They are more efficient and use less energy
- Greater control over the movement
Disadvantages of double cylinders
- They are more expensive than single-acting cylinders
- Bigger housing might be required
If you need your equipment to perform a movement in one direction you should choose a single-acting hydraulic cylinder. If the moving part of your machine has to move in two directions, you should use a double-acting hydraulic cylinder.