The Cylinder That Hammered at Full Stroke: Cushioning and Flow Control, Not the Cylinder
A pneumatic cylinder extending and hitting the end stop at full speed. It made a loud bang every cycle. The customer thought the cylinder was defective. It was fine. It had no end-position cushioning. The piston was slamming into the end cap. This is about pneumatic cylinder cushioning, not about the cylinder being broken.
Why cylinders hammer
A basic pneumatic cylinder moves at full speed until the piston hits the end cap. At 6 bar, a Ø50 cylinder moves at 500 mm/s. The kinetic energy at the end is absorbed by the end cap. After thousands of cycles, the end cap cracks. The piston rod bends. The cylinder wears out prematurely.
The cushioning options
| Type | How it works | Best for |
|---|---|---|
| No cushioning (basic) | Full speed to end stop | Light loads, low speed |
| Adjustable pneumatic cushion | Trapped air at end, bled through needle valve | Most cylinders (standard) |
| External shock absorber | Hydraulic shock absorber at the end of travel | Heavy loads, high speed |
| Rubber bumpers | Elastomer pads in the end caps | Light loads, short stroke |
| Flow control valves | Restricts exhaust, slows the whole move | Any cylinder (not just ends) |
What we did
1. Adjusted the end cushioning. The cylinder had adjustable cushioning (needle valves at both ends). We turned them in to slow the last 10 mm of travel. The piston approaches the end at 50 mm/s instead of 500 mm/s. It seats softly. The bang disappeared.
2. Added flow controls. We installed one-way flow control valves on the exhaust ports. The cylinder’s speed is set (not full speed). We set it to 200 mm/s. The kinetic energy at the end is 1/6 of the full-speed value. The cushioning handles it easily.
3. Added external shock absorbers. For the heavy-load application (20 kg at 500 mm/s), we added hydraulic shock absorbers at both ends. They absorb the impact regardless of the load. The cylinder now reaches the end softly, every cycle.
The adjustment procedure
Run the cylinder at operating pressure and load. Turn the cushioning needle valve in (clockwise) until the end-of-stroke is soft. If it’s too slow, back it off. The right setting: the cylinder reaches the end with a “thud,” not a “bang.” The last 10 mm should take 0.1-0.2 seconds. If the cushioning is too tight, the cylinder may not reach full stroke.
The cylinder cushioning rule: A cylinder that hammers at the end needs adjustable cushioning. Turn in the needle valves. Add flow controls to slow the overall speed. Use external shock absorbers for heavy loads. The cylinder that hammered wasn’t broken — it was running at full speed into a hard stop.
