The Castair DM75 is a 3/4 HP motor designed to mount a Castair refrigerated compressed air dryer directly onto your compressor. Specifically, it's listed for the RD59-11K dryer and smaller — Castair's lineup of refrigerated dryers rated at 59 CFM and below. The DM75 comes with a 3/4-inch NPT 3-ball valve bypass, metal flex hose, and vibration pads, giving you everything needed to mount the dryer on the compressor unit itself rather than on the wall or floor nearby.
Why Mount the Dryer on the Compressor?
Refrigerated compressed air dryers are most commonly wall-mounted or floor-mounted downstream of the compressor and tank. That's the standard installation — and it works fine. But compressor-mounted installation has practical advantages in smaller shops or installations where floor space is tight:
- Single footprint: Compressor and dryer occupy one location instead of two
- Shorter plumbing runs: Dryer connects directly to the compressor discharge, reducing the amount of piping needed
- Cleaner installation: No separate mounting bracket, wall hardware, or floor stand required
- Easier relocation: If the compressor moves, the dryer moves with it
The trade-off is that the dryer must be sized appropriately to handle the compressor's discharge temperature and CFM. At compressor discharge, air temperatures can reach 100°F or higher. Castair refrigerated dryers are rated at 100°F inlet and 100°F ambient. If your compressor discharges hotter than 100°F, dryer capacity is derated — at 150°F inlet, capacity drops to 55% of the rated CFM. For the RD59-11K mounted via DM75, that means at 150°F inlet air you're effectively getting 32–33 CFM of drying capacity rather than 59 CFM.
Compatible Dryer Models
The DM75 motor mount kit is designed for Castair refrigerated dryers in the RD59-11K size and smaller:
- RD25-6K: 25 CFM @ 37°F dew point, 3/4" NPT, 115V/1ph, 3.0A, 57 lbs, 10.6x17.9x19.6"
- RD59-11K: 59 CFM @ 37°F dew point, 3/4" NPT, 115V/1ph, 6.5A, 73 lbs, 10.6x19.1x22.4"
For the RD71-15K or larger dryers, use the DP100 instead — a standalone bypass plumbing kit that does not mount directly to the compressor.
What's Included with DM75
- 3/4" NPT 3-ball valve bypass assembly — allows dryer to be isolated for service without shutting down the compressor
- Metal flex hose — absorbs vibration between compressor discharge and dryer inlet, reducing stress on dryer connections
- Vibration isolation pads — isolates dryer from compressor vibration to extend dryer life
About Castair Refrigerated Dryers
When you add the DM75 mounting kit, you're pairing it with one of Castair's refrigerated dryers. Here's what those dryers do and how they're built:
- 37°F dew point: All Castair refrigerated dryers are designed to maintain a 37°F pressure dew point, which ensures that at the point of expansion (air tools, paint guns, pneumatic controls), condensation is minimal even in warm shop conditions
- Refrigerant: R134a and R407c — environmentally friendly refrigerants with quick-connect for recharge
- Heat exchanger: Stainless steel for even heat transfer and longevity
- Drain: Automatic moisture drain that only cycles when water is present — conserves compressed air compared to timer-based drains
- Electrical: 115V, 1-phase, 60Hz with 9-foot three-prong cord
- Max inlet pressure: 232 psig
- No programming required: Simple dew point indicator, no computer logic
- UL listed
When to Choose DM75 vs. DP100
- DM75 (this unit): For compressor-mounted installation on RD59-11K or smaller dryers. Use when you want the dryer physically on the compressor and your dryer is in the smaller size range.
- DP100: For RD71-15K or larger dryers. This kit plumbs the bypass but does not mount the dryer on the compressor — the dryer stands alone or is wall-mounted. Use when the dryer is too large or heavy for compressor mounting, or when a separate mounting location is preferred.
Why Buy From Air Compressor Factory Direct?
- Specialist since 2016 — we stock Castair dryers and mounting accessories
- Free shipping on qualifying orders
- Free tech support at 866-217-0063 — we can help you size the right dryer and confirm the DM75 fits your installation
- Full manufacturer warranty on all Castair equipment
- Honest guidance — if you need the DP100 or a larger dryer, we'll tell you before you order
Call 866-217-0063 for quick answers and help!
