If you need power, there’s nothing like a hydraulic cylinder to deliver a big punch. It’s the workhorse of the industrial world for the heaviest lifters and movers, including bulldozers and dump trucks. Hydraulic cylinders are commonly used in mobile applications. Bore sizes can range from a few inches to several feet in diameter.
Pneumatic cylinders are typically used on industrial machinery and rely on compressed air pressure from 15-110 psi. Pneumatic cylinders tend to have less overall cost associated when compared to hydraulic cylinders. Pneumatic cylinders offer more main body choices, including extruded aluminum profiles for easier integration into machinery.
Designing around them requires knowledge of pressure, force, and safety considerations. But it all starts with understanding the difference between a single and double acting hydraulic cylinder.
The heart of the device is the actuating cylinder piston which has pressurized air or hydraulic fluid pumped against it. If the fluid comes in one side and pushes the piston, it’s a single acting type. If there is fluid on both ends with a return line, it is double acting. That’s what it comes down to – whether you have one air or hydraulic service line at one end or two lines, one at each end.
Here's how a double acting pneumatic cylinder works: Compressed air is forced into the port at one end of the cylinder to push the piston forward, then into the opposite port to push the piston back. The alternating pressure moves the load a specified distance and then automatically retracts the piston for the next forward stroke. This process can be accomplished with a simple on-off control valve.
Here's how a double acting hydraulic cylinder works: Hydraulic fluid is pumped into one port to extend the piston, then pumped into the opposite port to return the piston to its original position. This is essentially the same as for the pneumatic cylinder, except that the two service lines carry hydraulic fluid instead of compressed air.
A single acting cylinder is simpler, so there is less to maintain. With only one line, the action of the cylinder is determined entirely by the pressure on that one line. They often have a spring or something similar to push or retract the piston rod, but they might rely on the force on end to push it back. Simplicity is always good for equipment that needs to be rugged and reliable.
A double acting cylinder alternates cycles of pressurized fluid to both sides of the piston and creates extend and retract forces to move the piston rod, permitting more control over the movement. Using a control system made up of a 2-, 3-, 4- way position valve would be required to achieve the desired movement for your application.
What it comes down to when selecting which type of cylinder is the amount of control that you need versus what you can afford to have in place. If the heavy lifting, so to speak, is only in one direction, a single acting hydraulic or pneumatic cylinder may be your best bet. If you are moving a part in two directions and need to have full control, it’s best to have a double acting hydraulic or pneumatic cylinder.
Be sure to discuss your application with a technical sales professional who can assist you with your cylinder selection and offer you other tips that you may not have considered when choosing the right hydraulic or pneumatic cylinder for your application.
The workhorses of linear power delivery are always going to be hydraulic or pneumatic cylinders. Whether you need control or ruggedness can often be how you make your choice. Whether the simplicity of a single or double acting hydraulic cylinder is your best bet, you can be sure that with the right design the force will always be with you.
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