Cast Air OR2 — 2" O-Ring for Air Compressor Tank Inspection Plug
This is the Cast Air OR2, a 2" O-ring designed specifically for use with the 2" inspection plug on Cast Air air compressor tanks. If your tank inspection port is leaking — either slowly seeping air at the plug or weeping moisture — this O-ring is almost certainly the cause. It is a wear item. It sees pressure cycling and temperature cycling every time the compressor runs, and over time the rubber hardens, compresses permanently, or develops small tears that prevent a reliable seal. Replacing it is a five-minute job that costs less than five dollars and eliminates the leak entirely.
This O-ring is the correct size and material specification for Cast Air tank inspection plugs. Using an off-the-shelf O-ring from a hardware store is a gamble — the dimensions may be close but not exact, and the rubber compound may not be rated for the pressures and temperatures inside a compressor tank. The OR2 is the right part for the job.
What the Inspection Plug and O-Ring Do
- Inspection plug (IP2): The 2" threaded plug that seals a port in the compressor tank. This port allows inspection of the tank interior and drainage of accumulated moisture. It is installed at the factory and rarely removed unless inspection or maintenance is required.
- O-ring function: The OR2 O-ring seats between the plug body and the tank port face (or in a groove on the plug itself), providing the primary seal that holds tank pressure. Without a good O-ring, the plug may appear tight but will leak at the sealing surface.
- When to replace: Any time you remove the inspection plug for tank inspection or moisture draining, replace the O-ring before reinstalling the plug. This is standard practice. O-rings that have been compressed under pressure for extended periods often will not reseal reliably when reinstalled.
Identifying When This O-Ring Has Failed
- Visible leak at inspection plug: Soap test shows bubbles forming around the plug threads or seating face
- Compressor cycling more frequently: A slow tank leak causes pressure to drop faster, triggering the pressure switch sooner than it should
- Audible hiss near the plug: A failed O-ring may produce a faint hissing sound when the tank is at operating pressure
- Moisture staining around the plug: Even a minor seep can leave rust staining or moisture streaks on the tank surface near the plug
- Previous removal of the plug: If the plug has been removed at any point for inspection or cleaning, the O-ring should be replaced as a matter of course before reinstalling
Installation Notes
- Depressurize the tank completely before removing the inspection plug. This is not optional.
- Clean the seating surface on the tank port and the plug body before installing the new O-ring. Any grit, rust, or old rubber residue will prevent the new O-ring from sealing correctly.
- Lubricate lightly with a compatible O-ring lubricant or clean compressor oil before installation. This helps the O-ring seat properly and prevents tearing during installation.
- Do not overtighten the plug. The O-ring does the sealing work. Overtightening crushes the O-ring beyond its design compression and can damage it immediately.
- Pressure test after reinstalling the plug. Run the compressor to operating pressure and soap-test the plug before returning the machine to service.
Related Parts
- IP2 — 2" Inspection Plug: The plug itself. If the plug is damaged, corroded, or cross-threaded, replace the whole plug along with the O-ring.
- OR2 — 2" O-Ring (this part): The sealing O-ring. Replace whenever the plug is removed or if a seal leak is present.
If your plug is in good condition, you only need the OR2. If the plug has been damaged or the threads are questionable, order the IP2 inspection plug and install a fresh OR2 with it.
Technical Specifications
- Part Number: OR2
- Description: 2" O-Ring for Inspection Plug
- Application: Cast Air air compressor tank inspection port
- Compatible plug: IP2 (2" Inspection Plug)
- Size: 2" nominal
- Price: $4.62
Why Buy From Air Compressor Factory Direct?
We stock Cast Air OEM replacement parts including the OR2 O-ring because getting the right specification matters even on small parts. An O-ring that is 0.05" too large in cross-section or 1/8" off in ID will not seal correctly, and you will be back to troubleshooting a leak that should have been fixed. The OR2 is the correct part for Cast Air inspection plugs — dimensionally accurate and made from the appropriate rubber compound for compressor service.
- Free shipping on qualifying orders
- Free tech support: Call 866-217-0063 if you are not sure whether the OR2 is the right O-ring for your specific Cast Air model
- Full manufacturer warranty on all parts
- Honest guidance: We will tell you if you need just the O-ring or the whole inspection plug assembly — not just add both to your cart
Call 866-217-0063 for quick answers and help!
