The Cylinder That Slammed Into Its Stops
A pick-and-place cylinder extended at full 6 bar pressure. The customer wanted it faster. They opened the flow control all the way. The cylinder shot across 200 mm in 0.3 seconds and slammed into the end cap — the impact shook the fixture, the part shifted, and the cylinder’s cushion did nothing (it was sized for a slower speed). After three months, the end cap cracked, the seal blew, and air sprayed across the line. The root cause was not the cylinder — it was a flow control that was treated as an on/off valve. Flow controls are not “open for speed”; they are precision adjustments that balance speed against impact.
Pneumatic cylinder speed is controlled by flow controls — but only if you use them correctly. Here is how to adjust them without destroying the cylinder.
Flow Controls: Meter-Out, Not Meter-In
A flow control valve restricts the air to or from the cylinder. There are two configurations:
- Meter-in: Restricts the air entering the cylinder. Slow to start, but the exhaust is unrestricted. This causes jerky motion (the load can run away).
- Meter-out: Restricts the air leaving the cylinder (the exhaust). This controls the speed smoothly — the air behind the piston acts as a cushion. This is the correct configuration for most pneumatic cylinders.
The rule: use meter-out (exhaust-side) flow controls on both ports. The cylinder that slammed into its stops had the flow controls installed as meter-in (intake-side). The exhaust was unrestricted, so the cylinder ran away at the end of stroke.
The flow control rule: Install flow controls on the exhaust side (meter-out). This gives smooth, controlled speed. Meter-in causes runaway and jerk. The cylinder that slammed was a meter-in installation.
Why You Do Not Run the Cylinder at Full Speed
A cylinder at full pressure and full flow moves fast — but it impacts the end cap hard. The end cap cushion (a built-in restrictor at the end of stroke) is designed to absorb the impact at a moderate speed. At full speed, the cushion cannot absorb the energy, and the piston hits the end cap. The fix is not a stronger cylinder — it is a slower speed. A 200 mm stroke at 0.5 m/s takes 0.4 seconds. That is fast enough for most pick-and-place. Running at 2 m/s saves 0.3 seconds but destroys the cylinder in months.
The Speed You Actually Need
Cylinder speed is selected by the cycle time, not by the maximum. If the cycle allows 0.5 s for the extend, and the stroke is 200 mm, the required speed is 0.4 m/s. Set the flow control to achieve that. Do not “open it all the way” and see what happens — calculate the speed first. Most pick-and-place applications work at 0.3–0.8 m/s. Above 1 m/s, the impact becomes a problem.
Adjusting the Flow Control: The Procedure
- Set the flow control at mid-range (turn fully closed, then open 2 turns).
- Cycle the cylinder once; observe the speed and end-of-stroke impact.
- If it is too slow, open the control a quarter turn.
- If it slams at the end, close it a quarter turn.
- Repeat until the cylinder moves at the target speed with a soft end-of-stroke.
- Lock the adjustment (the locknut on the flow control).
- Run 20 cycles; verify consistent speed and no banging.
When the Cylinder Will Not Slow Down
If the flow control is fully closed and the cylinder still moves fast, there is an internal bypass: the piston seal is leaking, or the flow control is installed on the wrong port. Check which port the flow control is on. On a double-acting cylinder, you need a flow control on both ports (one for extend, one for retract). If only one is installed, the other direction is uncontrolled.
A Cylinder Speed Checklist
- What speed does the cycle require (m/s)?
- Are flow controls installed on both ports (meter-out)?
- Is the cylinder speed below 1 m/s (impact safe)?
- Does the end-of-stroke impact sound soft (not a bang)?
- Is the flow control adjustment locked (locknut)?
- Does the cylinder move smoothly (no jerk)?
- After adjustment, does the speed stay consistent over 20 cycles?
- Is the end cap cushion set correctly (if adjustable)?
- Has the cylinder been re-adjusted after a load change?
- Is there any air leak past the piston seal (drift)?
The Bottom Line
The cylinder that slammed into its stops was a flow control used as an on/off valve. Pneumatic speed is set by meter-out flow controls, adjusted to the cycle’s required speed, and locked. The cylinder that lasts is the one that moves at 0.5 m/s with a soft stop — not the one that shoots across at 2 m/s and cracks its end cap.
