Controlling the speed of a pneumatic cylinder is one of the most common adjustments made during machine commissioning and production changeovers. Unconstrained cylinders move at maximum speed — often too fast for safe and reliable operation. Pneumatic speed controllers (also called flow control valves) give you precise, adjustable control over cylinder extend and retract speeds. This guide explains how they work and how to use them correctly.
How a Flow Control Valve Works
A pneumatic flow control valve contains a variable needle orifice — a tapered needle that can be screwed in or out to increase or decrease the aperture through which air passes. Reducing the aperture restricts flow and slows the cylinder. Opening it increases flow and speeds the cylinder up.
Most flow control valves also incorporate a one-way check valve. This is what makes meter-out (exhaust throttling) possible — the check valve allows free flow in one direction and forces all flow in the other direction through the needle orifice.
Meter-In vs Meter-Out
This is the most important concept in pneumatic speed control:
Meter-in restricts the air entering the cylinder. The needle valve is placed in the supply line. This creates a controlled build-up of pressure behind the piston.
Meter-out restricts the air exhausting from the cylinder. The needle valve is placed in the exhaust path. The air on the supply side fills the cylinder unrestricted; speed is controlled by how fast the exhaust side empties.
Meter-out is almost always the correct choice for pneumatic cylinders. Metering the inlet causes an “air spring” effect — if the load suddenly reduces, the compressed air behind the piston accelerates it to maximum speed. Meter-out maintains back-pressure in the exhaust side throughout the stroke, providing damping and consistent speed regardless of load variation.
Inline vs One-Touch Speed Controllers
Inline flow control valves screw into BSP threaded ports (typically the cylinder ports) with push-in tube connections on the other side. They are compact and mount directly on the cylinder.
Banjo-type speed controllers use a banjo fitting to mount at the cylinder port, allowing a very low-profile installation.
Inline tube-to-tube speed controllers fit into the tube run between the valve and cylinder — useful where the cylinder port is not easily accessible.
Setting Cylinder Speed Correctly
During commissioning, start with both speed controllers fully open and reduce the needle valve gradually until the cylinder moves at the desired speed. Then fine-tune:
- Start with the meter-out setting — restrict the exhaust until the cylinder moves smoothly at the target speed
- Check that the cylinder reaches the end of stroke with enough force and does not stall mid-stroke
- Adjust pneumatic cushioning (if fitted) separately — cushioning smooths the deceleration at end of stroke, while speed control sets the overall velocity
- Verify performance under full production load, as an unloaded cylinder may behave differently under the working load
Locking Settings to Prevent Drift
Once set correctly, flow control valve settings should be locked to prevent accidental or unauthorised adjustment. Most speed controllers have a locking nut or screw that fixes the needle position. Use it — a cylinder running at the wrong speed is a safety risk and a productivity problem.
Parker manufactures a comprehensive range of pneumatic flow control valves and speed controllers in all standard port sizes. Browse Parker flow control valves at Captivair for specifications and pricing.
Frequently Asked Questions
What is the difference between meter-in and meter-out in pneumatic speed control?
Meter-in restricts the air entering the cylinder, controlling how fast pressure builds behind the piston. Meter-out restricts the exhaust air leaving the cylinder. Meter-out is almost always preferred for pneumatic cylinders because it maintains back-pressure on the exhaust side throughout the stroke, giving consistent damped speed control regardless of load changes. Meter-in can cause sudden uncontrolled acceleration if the load reduces.
Why does my pneumatic cylinder surge at the start of stroke?
Surging at the start of stroke is usually caused by incorrect speed controller configuration. If you are using meter-in control, switch to meter-out. If already using meter-out, check that the exhaust side flow controller is correctly restricting (not fully open) and that the check valve in the flow controller is oriented correctly in the exhaust direction.
Where should I fit a speed controller on a pneumatic cylinder?
For meter-out control, the speed controller should be fitted at the cylinder port itself, oriented so the needle valve restricts the exhaust air and the check valve allows free flow in (from valve to cylinder). Fitting the speed controller close to the cylinder port minimises the dead volume between the controller and the cylinder, giving better speed response.
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