Double Acting Cylinder
Linear actuators produce linear motion as its output. It consists of a rigid cylinder capable of withstanding the pressure supplied to it. Each cylinder is provided with a maximum of two ports for supplying pressurized oil and for collecting return oil. A piston with the output shaft connected to it is placed inside the cylinder. The piston along with the output shaft can move freely back and forth inside the cylinder along its axis. Inner surface of the cylinder is highly polished to make a close fit with the piston to ensure a smooth and steady piston movement. Piston seals are provided on the piston to avoid oil leak when oil is allowed to expand inside the cylinder. The output rod is provided with rod end eye for connecting with the end equipment.
Output shaft is also called output rod.
The movement by which the output shaft or rod extends out of the cylinder is referred as forward stroke.
The movement by which output shaft retracts into the cylinder is referred as reverse stroke.
Double acting cylinder has two ports F and R each on either end of the cylinder. The output shaft connected to the piston protrudes out from only one side. Direction of output shaft movement is controlled by appropriately directing the pressure supply through the ports F and R. When pressure supply is introduced in to the cylinder through port F, the piston is pushed towards the right and oil in the right side of the piston is directed to the reservoir. Thus the output shaft executes forward stroke when pressurized oil is supplied to port F. To reverse the direction of the output shaft, direction of fluid flow is reversed. Now pressure supply is introduced through port R so the piston is pushed towards left and the output shaft retracts into the cylinder producing reverse stroke. Direction of fluid flow is changed with a four way direction control spool valve. Cushioning mechanism is provided to prevent damages and vibrations produced due to the impact of piston on the cylinder ends.
