Hydraulic Cylinders

By Jeff Bready, CFPS

A cylinder is an actuator that converts fluid power pressure and flow into mechanical linear motion; this can also be converted to limited rotary motion by levers, rack and pinions, and other means.

Hydraulic cylinders are found on presses, conveyors, lifts, dump trucks, garbage trucks, compactors, and clamps. All systems are designed by starting with the actuator.

What work do you want to perform? What is the weight of the load? Is it a vertical or horizontal movement? What distance does it have to travel? What time is allowed to extend and to retract? Fluid power can be pneumatic by using a gas such as air or hydraulic by using liquids such as mineral oils, water, synthetic oils or phosphate ester fluids.

The most common industrial cylinder is an NFPA tie rod double acting cylinder, which means the cylinder is powered in both extension and retraction. This cylinder type consists of a tube, tube seal, piston, piston seal, rod, rod seals, rod cartridge and end caps bolted with tie rods. They come with a wide variety of mounts such as: base, flange, trunnion and pivot. Proximity switches can be incorporated to give either end of stroke position indication or electronic feedback for infinite position control throughout the stroke of the cylinder. Some of the other types of cylinders are mill type, telescopic, multi-position and agricultural.

What type of piston seals and materials should be used? What size rod ensures it will not buckle? Does the application require a metallic rod scraper? Does it require one or more cushions? These and many other questions can be answered by contacting the Fluid Power Specialists at Quality Hydraulics & Pneumatics, Inc. to determine which hydraulic cylinder will work best for your application.