Meter-Out vs Meter-In Speed Control: How to Choose and Decode SMC AS Speed Controllers
2026-11-03A cylinder that moves too fast slams into its end stops; one that moves too slowly costs cycle time. Most machines fix this with a speed controller, a one-way flow control valve fitted at the cylinder port. Where you throttle the air matters, though. Throttle the wrong side, or mount the valve backwards, and the needle does nothing while the piston rod lurches out. This guide uses the official SMC AS series and Festo GRLA/GRLZ catalogues to explain meter-out versus meter-in control, how to tell the two apart from the part number, and what to check during installation.
How a speed controller works
A typical cylinder speed controller combines an adjustable needle valve with a check valve. In the controlled direction, air has to pass the needle and is throttled. In the opposite direction, the check valve opens and air flows almost freely. That makes every speed controller directional, so the first decision is which air stream you want to restrict.
- Meter-out (exhaust air flow control): supply air flows freely into the cylinder; exhaust air leaving the cylinder is throttled.
- Meter-in (supply air flow control): supply air entering the cylinder is throttled; exhaust air flows freely out.
Meter-out or meter-in: which one to use
Festo’s GRLA/GRLZ catalogue is clear about where each method fits:
- Double-acting cylinders: use exhaust air flow control. With free-flowing supply air and throttled exhaust air, the piston moves between two air cushions, which Festo says improves motion even when the load changes.
- Single-acting cylinders: the extend and return strokes share one port, so you need both supply and exhaust one-way flow control to set the two speeds independently. Alternatively, a flow control valve without a check valve throttles both directions at once; Festo notes this approach is often used on single-acting or small cylinders because it is simple.
SMC also offers the ASD dual speed controller, which integrates two needle valves and two check valves in one body so it can meter in and meter out at the same time. SMC lists its uses as preventing stick-slip, controlling single-acting cylinders, keeping speed stable under load fluctuation and low-speed control of small-bore cylinders.
| Application | Usual method | Notes |
|---|---|---|
| General speed control of a double-acting cylinder | Meter-out, one valve per port | Festo: smoother motion under changing load |
| Single-acting cylinder | Meter-in plus meter-out, or bidirectional throttling | One port, so both directions must be handled |
| Low speed, stick-slip prevention | SMC ASD dual speed controller | Meter-in and meter-out in one valve |
| Adjusting air blow flow | Restrictor without check valve | SMC recommends the -X214 or -X21 option, not a standard speed controller |
Decoding an SMC AS speed controller part number
SMC’s catalogue for the push-lock AS-F series uses AS2201F-01-06SA as its ordering example. Each field means:
| Field | Example | Meaning |
|---|---|---|
| Body size | 2 | 1: M5; 2: 1/8 and 1/4; 3: 3/8; 4: 1/2 |
| Type | 2 | 2: elbow; 3: universal |
| Control type | 0 | 0: meter-out; 1: meter-in |
| Fitting | 1F | With One-touch fitting |
| Thread type | Nil | Nil: R; N: NPT; G: G thread (face seal) |
| Port size | 01 | 01: 1/8; 02: 1/4; 03: 3/8; 04: 1/2 (M5 on body size 1) |
| Tubing O.D. | 06 | Metric: 23 = ø3.2, 04 = ø4, 06, 08, 10, 12 and 16 for ø6 to ø16 |
| Seal method | S | Nil: without sealant; S: with sealant |
| Lock type | A | A: push-lock type |
So AS2201F is an elbow meter-out controller, AS2211F an elbow meter-in controller, and AS2301F and AS2311F are the universal-type equivalents. Part numbers without the trailing A are the version that locks the needle with a lock nut.
You can also tell them apart on the machine. According to SMC, the knob is grey on meter-out types and light blue on meter-in types, while the release button is light grey for metric tubing and orange for inch tubing.
Key AS-F specifications (push-lock, brass)
- Fluid: air
- Proof pressure: 1.5 MPa
- Maximum operating pressure: 1 MPa; minimum operating pressure: 0.1 MPa
- Ambient and fluid temperature: −5 to 60 °C (no freezing)
- Tubing: nylon, soft nylon, polyurethane, FEP, PFA (take care at maximum pressure with soft nylon or polyurethane)
For comparison, Festo’s GRLA/GRLZ catalogue lists 0.2 to 10 bar operating pressure and −10 to 60 °C ambient and media temperature for the QS push-in versions. GRLA is the exhaust air (meter-out) valve and GRLZ the supply air (meter-in) valve.
Installation and adjustment checklist
- Check the flow direction. SMC warns that a valve mounted backwards will not control speed and the actuator may lurch suddenly. Match the flow symbol on the body before you fit it.
- Start fully closed and open slowly. Close the needle completely, then open it gradually until you reach the target speed. Clockwise closes the needle and slows the actuator; counterclockwise opens it and speeds it up.
- Lock the setting. On push-lock types, press the knob down and confirm it no longer turns either way. On lock-nut types, tighten the nut, because a loose nut lets the speed drift.
- Do not use pliers or over-rotate the knob. The needle is retained so it cannot fall out; forcing it past fully open causes damage.
- Do not use a speed controller as a shut-off valve. SMC states these products allow some leakage, and cranking the needle shut to stop all leakage can damage the equipment.
Published flow figures (sonic conductance C and critical pressure ratio b) are representative values. Real cylinder speed also depends on tubing length and size, the solenoid valve and the load, so the final setting is always made on the machine. For sizing the cylinder itself, see our pneumatic cylinder bore sizing guide; for choosing the valve that drives it, see the directional control valve guide. If you are matching mini cylinders across brands, the ISO 6432 cylinder cross reference may also help.
FAQ
How many speed controllers does a double-acting cylinder need?
Usually two meter-out controllers, one on each port, so extend and retract speeds can be set separately. If only one direction needs control, fit one on the port that exhausts during that stroke.
Why won’t my cylinder slow down after fitting a speed controller?
First check that it is not mounted backwards and that a meter-in valve has not been fitted where a meter-out valve was intended. Then confirm the needle was adjusted from fully closed and that the lock is engaged.
Can a single-acting cylinder use a standard meter-out valve?
Only for one direction. To set extend and return speeds independently you need a meter-in and meter-out combination, or a dual speed controller such as the SMC ASD. SMC also notes that the return speed of a single-acting cylinder varies with operating conditions, so check the maximum return speed table in its catalogue.
Can I use a speed controller to adjust an air blow nozzle?
SMC says speed controllers are designed to control actuator speed; for air blow, use a restrictor without the check valve function (-X214 or -X21).
Need help matching a part number?
Send us the cylinder model, bore, port thread and tubing size, and we will help you check which speed controller fits: doskee@dustry.ltd.
Sources: SMC catalogue “Speed Controller with One-touch Fitting AS Series, Push-lock Type” (How to Order, Specifications, Specific Product Precautions); SMC “ASD Series Dual Speed Controller” catalogue; Festo “One-way flow control valves GRLA, GRLZ” catalogue. Always confirm details against the manufacturer’s latest official documentation.