Detailed introduction to the working principles of different types of cylinders

Cylinder working principle


1. Single-acting cylinder


Only one chamber can input compressed air to achieve movement in one direction. Its piston rod can only be pushed back with the help of external force;usually with the help of spring force, diaphragm tension, gravity, etc.


The characteristics of single-acting cylinders are:



1) Only one end inlets (exhausts) air, the structure is simple and the air consumption is small.                                            


2) Use spring force or diaphragm force to reset, and part of the compressed air energy is used to overcome the spring force or diaphragm tension, thus reducing the force output of the piston rod.


3) Spring, diaphragm, etc. are installed in the cylinder, and the stroke is generally shorter;compared with a double-acting cylinder of the same volume, the effective stroke is smaller.


4) The tension of the cylinder return spring and diaphragm changes with the deformation, so the output force of the piston rod changes during travel.


Due to the above characteristics, single-acting piston cylinders are mostly used for short strokes. Its thrust and movement speed are not required in occasions such as air lifting, positioning and clamping devices. This is not the case with single-acting plunger cylinders, which can be used in long-stroke, high-load applications.





2. Double-acting cylinder


A double-acting cylinder refers to a cylinder that can input compressed air into two chambers respectively to achieve bidirectional movement. Its structure can be divided into double piston rod type, single piston rod type, double piston type, buffer type and non-buffer type. This type of cylinder is the most widely used.





Double-piston rod double-acting cylinder There are two types of double-piston rod cylinders: cylinder fixed and piston rod fixed.
When the cylinder is fixed, the load it carries (such as the workbench) is integrated with the two piston rods of the cylinder. The compressed air enters the two chambers of the cylinder in sequence (one chamber is for air intake and the other is for exhaust). The piston rod drives the workbench to move left and right. The movement range of the workbench is equal to 3 times its effective stroke s. The installation takes up a lot of space and is generally used on small equipment.
When the piston rod is fixed, for the convenience of pipeline connection, the piston rod is made hollow, and the cylinder and the load (workbench) are integrated. The compressed air enters the two chambers of the cylinder from the left or right end of the hollow piston rod, so that the cylinder drives the workbench. To move left or right, the movement range of the workbench is twice its effective stroke s. Suitable for medium and large equipment.





3. Buffer cylinder


1—Piston rod;2—Piston;3—Buffer plunger;4—Plunger hole;5—One-way seal;6—Throttle valve;7—End cover;8—Air hole





Buffer cylinder For cylinders with high speed near the end of the stroke, if necessary measures are not taken, the piston will hit the end cover with great force (energy), causing vibration and damaging the parts. In order to make the piston move smoothly at the end of the stroke without causing impact. Buffer devices are added at both ends of the cylinder, which are generally called buffer cylinders. The buffer cylinder is shown in the figure above. It is mainly composed of piston rod 1, piston 2, buffer plunger 3, one-way sealing ring 5, throttle valve 6, end cover 7, etc.
The working principle of the buffer cylinder is: when the piston moves to the right driven by compressed air, the gas in the right chamber of the cylinder is discharged through the plunger hole 4 and the air hole 8 on the cylinder head. When the piston moves near the end of its stroke, the buffer plunger 3 on the right side of the piston blocks the plunger hole 4. When the piston continues to move to the right, the remaining gas sealed in the right chamber of the cylinder is compressed and slowly passes through the throttle valve 6. And the air hole 8 is discharged. If the pressure generated by the compressed gas is balanced with all the energy of the piston movement, a buffering effect will be achieved, so that the piston moves smoothly at the end of the stroke without impact. By adjusting the opening of the throttle valve 6, the exhaust volume can be controlled, thereby determining the pressure in the compressed volume (called the buffer chamber) to adjust the buffering effect. If the piston is moved in the reverse direction, compressed air is input from the air hole 8 to directly open the one-way valve 5 and push the piston to move to the left. If the opening of throttle valve 6 is fixed and cannot be adjusted, it is called a non-adjustable buffer cylinder.​
There are many types of buffer devices installed in the cylinder, and the above is just one of them. Of course, measures can also be taken on the pneumatic circuit to achieve a wide variety of buffer devices installed in the cylinder.