(a) Cushion end Cylinder: A cylinder in which the piston has cushion nose on one side or both sides, for gradual deceleration of the piston near the end of its stroke is known as cushion end cylinder.
• It reduces the shock or the impact load on the end covers of the cylinder.
• Pneumatic cylinders are capable of very high speed and considerable shock; force can be developed on the end of the stroke. Smaller cylinders often have fixed cushioning i.e. rubber buffers to absorb the shock and prevent internal damage to the cylinder.
• On large cylinders, the impact effect can be absorbed by an air cushion that decelerates the piston over the last portion of the stroke.
• This cushion traps some of the exhausting air near the end of the stroke before allowing it to bleed off more slowly through the adjustable needle valve.
• The normal escape of the exhausting air to the outlet port is closed off as the cushion nose enters the cushion chamber, so that air can only escape through the adjustable restriction port. The trapped air is compressed to a relatively high pressure which breaks the inertia of the piston.
• When the piston reverses, the cushion chamber acts as a check valve to allow air flow to the piston. The cushioning stroke should be as short as possible.
• To decelerate heavy loads or high piston speeds, an external shock absorber is required.
• Cushions are not a speed controlling device.
• Effect of cushioning is very much dependent on the amount of cushion opening in the cylinder bore.