Double acting hydraulic cylinders work by admitting and removing pressurized oil, ether, mineral or water composites from an enclosed space. The pressure acts upon a piston with an attached rod that extends and retracts according to the amount of fluid in the chamber. Even a small motor with pressurized fluid can create tremendous work force. The popularity of hydraulic cylinders in agricultural, automotive, power generation, oil and gas, construction, demolition, material handling, aerospace and transport industries among others can be attributed to the significant energy gains they allow.
Double acting hydraulic cylinders can lift, turn, tilt, press, steer, pull and push heavy machine components and attached loads along any linear plane making them useful in cranes, lifts and braking mechanisms alike. While the length and plane of these hydraulic cylinders are fixed, double action offers powered motion for both extension and retraction whereas single action cylinders provide motion in only one direction. Although this requires a larger reservoir of compressed fluids, double acting hydraulic cylinders are often preferred over their unidirectional counterparts as they offer greater mechanical versatility, higher speed operation and tighter control.
While specific models may vary, the basic construction and function of double acting hydraulic cylinders remains relatively uniform. The main body of the cylinder is a round or rectangular tube shaped device enclosed at each end with a cap. This chamber houses and connects all other cylinder components. In one or both end caps there is a sealed hole through which the piston rod is extended and retracted as needed. A cold-rolled piece of metal or ceramic, the rod is attached to a piston within the main cylinder.
The hydraulic piston is a disc-like device that fits perpendicular to the cylinder walls, filling the cross-section of the barrel. This divides the cylinder into two separate compartments. Several seals are placed around the piston head and the rod opening to ensure that fluid does not leak in, out or from one side of the chamber to the other causing a loss of pressure and decreased functionality. In either end is an intake and exhaust valve where the fluid is introduced and removed.
When the pressurized fluid is forced into the section of the cylinder below the piston, the rod is extended while the inverse retracts it. The degree of piston rod extension and retraction correlates with the amount of fluid entered into the enclosed cylinder shaft. This length, known as the stroke, is one of the most important considerations when selecting the proper hydraulic cylinder for a given application. Additional concerns include body type and material, operating pressure, maximum working pressure, rod diameter and bore diameter.