The Castair B11.5 is a replacement V-belt for Cast Air air compressor drive systems. The B-section designation identifies this as a standard B-profile industrial V-belt — 21/32 inch top width, 13/32 inch depth — used in compressor drive applications where the pulley and sheave dimensions call for this cross-section. The 11.5 designation indicates the belt's pitch length in inches.
V-belts on air compressors are wear items. They stretch, crack, and glaze over time. On a cast iron two-stage compressor like the Cast Air C1 or C2 series, a worn belt means slippage at the pump sheave — lost CFM, increased motor load, and eventual belt failure. Keeping a spare on the shelf is standard practice for any shop that runs on compressed air.
Belt Identification
- Section: B (21/32" top width x 13/32" depth)
- Pitch Length: 11.5 inches (verify against your compressor's belt specification before ordering)
- Type: Standard industrial V-belt
- Application: Air compressor drive — motor pulley to pump flywheel/sheave
When to Replace
- Belt shows cracking along the sidewalls or bottom
- Belt surface is glazed (shiny, smooth) rather than matte — glazed belts slip
- Belt has stretched beyond the adjustment range of the motor mount
- Belt squeals under load at startup
- Visible fraying or chunking on the belt surface
Installation Notes
Always replace belts with the compressor depressurized and the disconnect locked out. On Cast Air compressors, the motor mount typically slides on rails for belt tension adjustment. After installing a new belt, set tension so the belt deflects approximately 1/2 inch under moderate finger pressure at the midspan. Recheck tension after the first 4-8 hours of operation — new belts seat and stretch slightly during break-in.
If your compressor runs a paired belt (some models use two matched belts), replace both belts at the same time. Running a new belt with an old stretched belt creates uneven loading and accelerates wear on both.
Compatibility Note
Manufacturer data for the B11.5 specifically is limited. Verify your compressor model's belt specification in the parts breakdown or on the manufacturer's label before ordering. Contact Cast Air at (320) 796-0851 or us at 866-217-0063 with your compressor model number to confirm the correct belt length for your unit.
What is in the Box
- One replacement V-belt, B11.5 specification
Why Buy From OEM Diagnostic Tools?
We have specialized in professional shop equipment since 2016. Free shipping on all orders, free technical support at 866-217-0063, and Cast Air manufacturer warranty. Call us with your compressor model number and we will confirm the correct belt before you order.
Call 866-217-0063 for quick answers and help!
