AD27-C-A Auto-Drain Bowl for SMC AF20/AW20 Filters

Technical specifications

Engineer’s tip: “Pay attention to the minimum trigger pressure — 0.1 MPa. If pressure in your line regularly drops below this threshold (for example overnight or when the compressor is idle), the auto drain simply won’t open, and residual condensate has to be drained manually,” notes Vitalie Boluchevschi, Chief Engineer at Acvatron SRL.

Design features

• Transparent polycarbonate housing allows visual monitoring of the condensate level without disassembly.
• Float mechanism: as condensate accumulates, the float rises, opens a small pilot valve, pressure enters the control chamber and pushes the main piston down — the drain opens without any operator action.
• N.C. type (normally closed): when there’s no pressure in the system, the drain valve stays closed, preventing spontaneous air or condensate leaks while the compressor is off.
• Compatible with the standard SMC size-20 modular air-preparation line — fits without modifying existing piping.
• Compact size and low weight make on-site replacement easy, without removing the entire filter from the line.

Installation guidelines

1. Depressurize the relevant section of the line before replacing the bowl.
2. Unscrew the standard bowl from the AF20/AW20 filter and remove the old seal.
3. Fit the new bowl seal (included) into the housing’s seat.
4. Thread the AD27-C-A bowl on by hand until snug — do not overtighten, as polycarbonate is sensitive to excessive torque and impact.
5. If required, connect a drain tube to the M5 × 0.8 port (or fit a plug if condensate does not need to be routed to a drain system).
6. Gradually re-pressurize the system and check the joint for leaks both visually and with soapy water.

Compatibility and equivalents

The AD27-C-A bowl fits SMC AF20 and AW20 series filters and filter-regulators. The designation AD27-A (without the drain-port thread suffix) is also common — the only difference is the drain-port execution, while the underlying float mechanism is identical.

⚠️ Thread mismatch warning: the drain port on this bowl uses a metric M5 × 0.8 thread — it is neither BSP (G) nor NPT. When sourcing a fitting or plug for the drain tube, the M5 metric thread can easily be mistaken for an imperial thread of similar visual diameter — they are not interchangeable, and forcing a mismatched fitting can strip the plastic housing’s threaded seat. Verify the thread with calipers, or confirm with an Acvatron specialist before ordering.

Common installation mistakes

• Overtightening the bowl with a tool — cracks the polycarbonate and causes leaks. The bowl should only be hand-tightened.
• Using an NPT/BSP fitting instead of the metric M5 × 0.8 on the drain port — strips the thread.
• Ignoring the minimum trigger pressure (0.1 MPa) — expecting auto-drain operation in a low-pressure system, causing the bowl to overfill.
• Installing without a new seal — micro-leaks at the housing/bowl joint.
• Abrupt pressurization/depressurization cycles — accelerates wear on the polycarbonate housing; frequent sudden pressure swings should be avoided.

Practical application examples

• Replacing a clouded or cracked stock bowl on an AF20 filter at a small workshop’s compressor station.
• Upgrading an air-preparation line from manual to automatic condensate drainage — useful for sites without permanent staff on hand.
• Fitting an AW20 filter-regulator in a paint-shop or woodworking pneumatic system, where visual monitoring of condensate level matters.

Expert opinion

“The AD27-C-A bowl is one of those parts that seems minor until you deal with the consequences of a missed manual drain: water in the line, corrosion inside pneumatic tool cylinders, valve malfunctions. For small compressors, especially under 0.75 kW, I always recommend the N.C. version — it prevents air leakage at compressor start-up, unlike N.O. versions,” comments Vitalie Boluchevschi, Chief Engineer at Acvatron SRL.

FAQ

Does the AD27-C-A fit the AF30 or AF40 filter? No, this bowl is sized for size-20 units (AF20/AW20). Larger filters use bowls from the AD37/AD47 series.

Do I still need to drain condensate manually if the auto drain is installed? Residual condensate that accumulates while the system is unpressurized should be drained manually at the end of the shift — the N.C. auto drain won’t open with no pressure in the line.

What’s the minimum pressure needed for the auto drain to trigger? 0.1 MPa — at lower line pressure, the float mechanism may not open the drain valve reliably.

Can I use a metal fitting in the M5×0.8 drain port? Yes, but the thread must be strictly metric M5×0.8 — not BSP and not NPT.