AS Speed Controller — Push-Lock Elbow, BSPP
The SMC AS series is the most widely used pneumatic cylinder speed controller in North American industrial automation — a needle valve with a one-touch tube fitting that mounts directly in the cylinder port line to regulate piston speed. As an authorized SMC Corporation of America distributor, Automation Distribution stocks 684 AS series speed controller SKUs covering every body size, mounting style, thread type, and specialty configuration: standard elbow, push-lock elbow, inline push-lock, stainless steel, with flow indicator, low speed, clean room, flame resistant, and tamper-proof variants.
How AS series speed controllers work
An AS speed controller installed between a solenoid valve and a cylinder port acts as a variable orifice in the exhaust line. As the cylinder extends or retracts, air leaving the opposite port passes through the needle valve — turning the needle clockwise reduces the exhaust orifice, slowing the piston. Turning counterclockwise opens the orifice, allowing the piston to move faster. This is called meter-out control and is the standard approach for most cylinder speed control applications because restricting exhaust (rather than supply) produces stable, consistent piston speed under varying loads.
Each cylinder port gets its own AS controller — one for extend speed, one for retract speed — giving independent control of both directions.
AS series configurations
AS — Standard elbow (NPT thread)
The base AS series: one-touch tube fitting on the tube side, NPT male thread on the port side, elbow body. Screws directly into the cylinder port or a valve sub-base port. Available in body sizes 1–4 covering M5, 1/8", 1/4", and 3/8"–1/2" NPT ports, with compatible tube OD from ø3.2mm (1/8") through ø16mm (5/8"). The standard choice for the vast majority of cylinder port speed control installations.
AS-F / AS-FM — Push-lock elbow and inline
Push-lock variants add a secondary locking mechanism to the one-touch collet so the tube cannot be accidentally released by pushing on the fitting body — important in high-vibration environments or where inadvertent tube release would be a safety or process concern. Available in elbow (AS_F) and inline (AS_FM) body styles. The FM inline version is specified when the cylinder port geometry or panel layout doesn't permit an elbow orientation.
AS-FG — Stainless steel, push-lock
Stainless steel body and needle for corrosion resistance in wash-down, food processing, outdoor, and chemical environments where standard zinc-alloy body would corrode. Available in elbow and inline configurations with push-lock tube retention. Specified as a direct replacement for standard AS controllers wherever the environment demands stainless wetted surfaces.
AS-FS / AS-FSM / AS-FSC — With flow indicator
The AS-FS adds a visible flow indicator window to the needle body — a colored indicator moves with the needle position, providing visual confirmation that airflow is occurring and indicating approximate needle setting without a separate gauge. Useful in multi-cylinder panels where visual status monitoring during commissioning or maintenance reduces diagnostic time. AS-FSM (metric thread indicator) and AS-FSC (combined metric/NPT) are variants for specific thread environments. Available in elbow configuration, body sizes 1–4.
AS-FM (Low Speed) — Fine flow control for slow cylinder applications
The low speed AS-FM variant uses a finer needle thread pitch and modified orifice geometry to provide precise flow control at very low flow rates — for applications requiring slow, controlled cylinder motion where the standard needle adjustment range is too coarse. Specified for press-fit operations, precise positioning strokes, and delicate part handling where consistent very low speed is required.
AS-FPQ / AS-FPG — Clean room series
Clean room AS speed controllers use fluororesin (PTFE-equivalent) internal seals and lubrication-free construction to eliminate particulate and outgassing concerns in semiconductor, pharmaceutical, and medical device manufacturing environments. AS-FPQ uses a conductive body for ESD-sensitive environments; AS-FPG uses a standard clean resin body. Both are available in elbow configuration with one-touch tube fitting.
JAS — With built-in one-touch fitting, compact
The JAS series integrates the one-touch fitting and speed controller needle into a single compact body — shorter overall length than the standard AS elbow where panel space is constrained. The built-in fitting accepts the same tube OD sizes as KQ2 fittings. Specified for tight cylinder port areas where a standard AS elbow would conflict with adjacent hardware.
Tamper-proof
Tamper-proof AS controllers include a locking cover or require a special tool to adjust the needle, preventing unauthorized speed setting changes after initial commissioning. Specified in applications where consistent cycle time is a quality or safety requirement and ad-hoc field adjustments must be prevented.
AS — BSPP (G thread), face seal
AS speed controllers with BSPP (G thread) port connections use a flat face seal rather than a tapered thread seal. Specified for cylinders and valve sub-bases with metric G thread ports — common in European-origin equipment operating in North American facilities, or in mixed metric/inch machine designs. The tube-side connection is the same standard one-touch fitting as NPT variants.
AS series part number guide
Example: AS2301F-N01-08A
AS = series; 2 = body size (1 = M5/ø3.2–4mm, 2 = 1/8" NPT/ø4–8mm, 3 = 1/4" NPT/ø6–10mm, 4 = 3/8"–1/2" NPT/ø8–16mm); 3 = suffix position (01 = standard, 11 = universal thread); 0 = body style; 1 = variant code; F = push-lock one-touch fitting; N01 = 1/8" NPT thread (N = NPT, G = BSPP/G thread, number = size); 08 = tube OD in mm (08 = 8mm); A = with sealant.
The body size number is the single most important selection digit — it determines both the port thread size range and the compatible tube OD range. Mixing body sizes with incompatible port/tube combinations is the most common ordering error on AS controllers. When in doubt, call 1-888-600-3080 — our application team can cross-reference from your cylinder port thread and tube size to the correct AS part number.
Meter-in vs. meter-out: which to use
AS speed controllers installed in the standard orientation restrict exhaust flow (meter-out). This is correct for the majority of horizontal and most vertical cylinder applications because back-pressure in the exhaust side stabilizes piston motion against varying loads. If installed in reverse orientation, they restrict supply flow (meter-in) — this is sometimes appropriate for vertical cylinders with heavy loads descending under gravity, where metering the supply prevents the load from free-falling ahead of the air. For most applications, meter-out is the correct default. If you're unsure which orientation is appropriate for your application, contact our technical team.