A hydraulic cylinder is a hydraulic actuator that performs linear motion. There are two styles, single rod cylinder, and double rod cylinder. This time, we are talking about the double-acting one.
The double-acting hydraulic cylinder has an oil inlet and an oil outlet on both sides of the piston and reciprocates by applying pressure to both sides. Are you curious about the inner structure of the cylinders? Let’s go and find it.
There includes a piston, a cylinder tube (cylinder block) and a piston rod (FIG. 1) in one double acting hydraulic cylinder. The protruding side of the piston rod is called the rod side and the side without the piston rod is called the cover side.
1. Push force
Push stroke is the stroke that pushes the piston rod out of the cover side (figure 1, left). When the hydraulic oil flows Q from the cover side port into the volume chamber, pressure p acts on the piston and exerts a force pushing the piston rod out (the force is F). The piston moves to the right at a speed of U, and the hydraulic fluid flows from the port on the rod side to the tank. At this point, F = Ac ×p and U = Q/A, respectively. A is the cross-sectional area of the piston under the pressure acting on the cylinder, which is called an effective cross-sectional area.
2. Pull force
The pull stroke is the return stroke of the piston rod to the cylinder tube (figure 1, right). When the hydraulic oil flows from the rod side port with flow Q, pressure p acts on the piston and exerts a force (the force is F) that returns the piston rod to the cover side. The piston moves to the left at a speed of U, and the hydraulic fluid flows at atmospheric pressure from the port on the cap side to the tank. The cylinder pulling force F and piston velocity U are expressed as F = A r ×p and U = Q/A r, respectively. A is the cross-sectional area of the effective piston on the rod side.
The push and pull force F is the ideal cylinder force, which is open to the downstream tank and it ignores all friction and leakage effects. Due to these effects, the actual cylinder force and piston speed will be reduced then.
Here comes the inner structure of double acting hydraulic cylinders. It’s mainly composed of a cylinder tube, front and rear cover, piston rod, piston and buffer plunger (figure 2).
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Post time: Mar-18-2020