Pneumatic Flow Control Valve: Setting Cylinder Speed
A flow control valve sets the stroke speed of a pneumatic cylinder by throttling the air in one direction and letting it pass freely in the other. This guide explains the design, the difference between meter-in and meter-out control, and how to mount and select the valve.
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How does a flow control valve work?
A flow control valve combines two functions in one body: an adjustable throttle and a parallel check valve. In one flow direction the air is throttled through an adjustable needle or spindle, while in the opposite direction the check valve opens and lets the air pass almost unrestricted.
As a result, the throttling acts on only one of the two air flows. The adjusting screw changes the free cross-section and therefore the volume of air that can pass per unit of time. This lets you set the piston speed steplessly from full throttle to open flow.
- Throttle direction: adjustable cross-section limits the air flow.
- Free direction: check valve opens and bypasses the throttle.
- Adjusting spindle usually locked with a lock nut.
- Body styles: push-in fitting, elbow and inline versions.
Meter-in or meter-out - which is better?
The key to smooth motion is which air flow you throttle. Meter-out control throttles the air leaving the cylinder, meter-in throttles the air entering it. For double-acting cylinders, meter-out is almost always the right choice.
With meter-out control a back pressure builds up in the exhausting cylinder chamber. The piston is clamped between supply pressure and back pressure and therefore moves smoothly and without jerking, even under changing loads. Meter-in control lacks this back pressure, so the piston tends to stick and slip and lunges forward when the load changes.
How do you mount and adjust the valve?
The valve works best directly at the cylinder port, ideally as a push-in fitting screwed into the cylinder cap. This keeps the trapped air volume small so the control responds quickly. Each cylinder uses two valves, one per direction of motion.
To adjust, run the cylinder with the throttle nearly closed and then open it slowly until the desired speed is reached. Set both directions separately and secure the spindle with the lock nut. Always check the behaviour under real load, since speed and back pressure change with the applied force.
- Screw the valve straight into the cylinder, not into the valve manifold.
- Watch the exhaust direction: the free path points into the cylinder.
- Open slowly from fully closed, not the other way around.
- Check both end positions and adjust cushioning separately.
- Lock the spindle after setting.
What matters when choosing a valve?
The important points are the port thread, the tube diameter and the nominal flow. The valve has to match the cylinder volume and the desired stroke time: too small a cross-section limits the top speed, too large a one makes fine adjustment difficult.
Frequently asked questions
Why throttle the exhaust air and not the supply air?
Meter-out control creates a back pressure in the exhausting cylinder chamber that guides the piston smoothly and without jerking. Meter-in control lets the piston stick, slip and lunge when the load changes. For double-acting cylinders, meter-out is standard.
How many flow control valves does a cylinder need?
A double-acting cylinder gets two valves, one per direction of motion, so extend and retract speeds can be set independently.
Does the valve change the cylinder force?
No. A flow control valve only limits the flow rate and therefore the speed. Operating pressure and the resulting force stay the same.
Where is the valve best mounted?
As close to the cylinder port as possible, ideally as a push-in fitting in the cap. The small trapped volume gives fast response and stable control.
Looking for the right flow control valve?
We supply flow control valves as push-in, elbow and inline versions for all common cylinders and tube sizes.
Smooth motion
Meter-out control for even piston movement.
Wide range
Push-in, elbow and inline styles from stock.
Stepless
Fine speed adjustment with lock nut.
Expert advice
We help with nominal size and port thread.