The Cast Air AFD1 is a float-operated automatic drain valve for compressed air filter bowls, priced at $77.77. It fits all Castair filter bowls via a 1/8" NPT connection. If you are running Castair inline filters — at individual shop drops, at the main line, or in a spray booth — and those filter bowls are collecting water that requires manual draining, the AFD1 makes the draining automatic. No timers, no solenoids, no electrical work. A mechanical float inside the bowl rises with the water level and opens the drain when the condensate reaches a threshold, then closes when the bowl is clear.
Filter bowls exist to pull moisture and particulates out of the air stream before the air reaches tools, paint guns, and pneumatic equipment. But a filter bowl is only useful if the condensate it collects actually gets removed. A bowl that overfills passes moisture downstream just like no filter at all. Manual bowl draining is one of those maintenance tasks that is easy to perform when someone remembers, and easy to skip when a shop is busy. The AFD1 removes the human element entirely.
How a Float Drain Works
Inside the AFD1 is a mechanical float — the same basic principle used in a toilet tank or a carburetor float bowl. As condensate collects at the bottom of the filter bowl, the float rises with the water level. When water reaches the drain threshold, the float mechanism opens a drain port and evacuates the condensate. When the bowl is drained, the float drops and the drain port closes. The cycle repeats automatically every time condensate accumulates. No electricity. No programming. No adjustments.
This passive mechanical approach is what makes float drains suitable for locations where running power to the filter is impractical — which describes most inline filter installations. The AFD1 threads directly into the bowl's existing drain port and replaces whatever manual drain fitting was there before.
Key Features
- Float-Operated Automatic Drainage: Mechanical float actuates drain port automatically — no timers, solenoids, or electricity required
- 1/8" NPT Connection: Threads into the standard drain port on all Castair filter bowls
- Universal Castair Bowl Fitment: Fits all Castair filter bowl sizes in the AFD series
- Passive Mechanical Operation: No consumable electronic components, no power supply, no timer battery
- Continuous Protection: Drains as condensate accumulates, not on a fixed schedule — matches actual moisture load
- Prevents Bowl Overflow: Keeps filter bowls operating within capacity so they actually filter instead of passing water
- Simple Installation: Thread-in replacement for existing manual drain fitting on compatible filter bowls
- Cast Air Quality: Built to the same manufacturing standard as the Castair compressor and filter product line
Why Filter Bowl Draining Matters
An inline compressed air filter does two things: it removes particulates and it separates condensate. The condensate collects in the bowl at the bottom of the filter housing. In a high-humidity environment or on a compressor that runs hard, a filter bowl can fill up in hours. When it fills, moisture carries over into the downstream air stream. At a spray gun, that means fisheye, blushing, and adhesion failures. At an air tool, it means accelerated internal corrosion and shortened tool life. At a pneumatic control, it means stuck valves and erratic operation.
The AFD1 keeps the bowl drained so the filter keeps doing its job. This is especially important at high-volume stations — main line filters, booth supply filters, and any point-of-use filter that sees significant airflow during peak hours.
What's in the Box
- 1x Cast Air AFD1 bowl float drain valve
- 1/8" NPT thread fitting for standard Castair filter bowl drain ports
Available Configurations
Cast Air offers two float drain valve options for filter bowls. The correct one depends on your filter bowl series:
- AFD1 — $77.77 (this part): Watts Bowl float drain. 1/8" NPT connection. Fits all Castair filter bowls. Use this if you have standard Castair inline filters.
- AFD3 — $47.74: THB Bowl float drain. 1/4" NPT connection. Fits Castair THB-series filter bowls specifically. Lower cost, different bowl series. If you have THB bowls, use the AFD3.
For automatic tank draining (the receiver tank itself, not the filter bowl), see the ADVS ($119.43) or ADVSM ($154.00) air-operated tank drain valves.
When Does a Shop Need the AFD1
Choose the AFD1 when:
- You have Castair inline filter bowls that currently require manual draining
- Your filter bowls are in a humid environment and accumulate condensate quickly
- You want automatic bowl draining without any electrical work at the filter location
- You are upgrading from manual drain petcocks on existing Castair filter bowls
- You are installing new Castair filters and want automatic drainage from the start
Choose the AFD3 instead when:
- Your filter bowls are the THB series — the AFD3 is the correct fit for THB bowls and is $30 less
Note on tank draining: The AFD1 and AFD3 are filter bowl drains only. They do not mount on or drain the receiver tank. For tank drain automation, use the ADVS or ADVSM air-operated tank drain valves.
Technical Specifications
- Part Number: AFD1
- Manufacturer: Cast Air (Castair), Minnesota
- Type: Bowl float drain valve — automatic, mechanical
- Connection Size: 1/8" NPT
- Compatible Bowl Series: All Castair filter bowls (Watts Bowl series)
- Operation: Mechanical float — no electricity required
- Drain Trigger: Float-activated when condensate reaches threshold level
- Price: $77.77
- Country of Origin: USA (Minnesota)
Why Buy From Air Compressor Factory Direct?
Air Compressor Factory Direct has stocked Cast Air compressors and accessories since 2016. We carry the full Castair filter and drain accessory line, so you can get both the filter and the correct drain valve from a single source. If you are not sure whether your bowl series takes the AFD1 or the AFD3, call us — give us the filter part number and we will tell you exactly which drain fits.
Every order ships free. Full manufacturer warranty. Our tech support is staffed by people who work with compressed air systems daily, not a general call center. We stock these parts because shops need them, and we will get you the right one the first time.
Call 866-217-0063 for quick answers and help!
