The Castair DP100 is the bypass plumbing kit for Castair refrigerated dryers in the RD71-15K size and larger — specifically designed for installations where the dryer is not mounted directly on the compressor. Unlike the DM75 (which physically mounts the dryer on the compressor), the DP100 is a standalone bypass assembly that plumbs the dryer into the air system with a proper 3-ball valve bypass, allowing you to isolate and service the dryer without shutting down your compressor. The dryer itself sits separately — wall-mounted, floor-mounted, or on a stand — and the DP100 handles the bypass plumbing between the compressor and the dryer.
Why Larger Dryers Need a Separate Installation
Castair's larger refrigerated dryers — the RD71-15K (71 CFM, 110 lbs), RD113-60K (107 CFM, 119 lbs), and RD161-37K (161 CFM, 137 lbs) — are too large and heavy to mount directly on the compressor. The weight alone makes compressor mounting impractical. These units need their own mounting location, typically near the compressor but supported independently.
The bypass plumbing is critical for any dryer installation, regardless of size: you need to be able to route compressed air around the dryer if it requires service, a refrigerant recharge, or if the dryer fails. Without a proper bypass, a dryer problem means the entire compressed air system is down. With the DP100 bypass in place, you open the bypass valve, close the dryer isolation valves, and the shop keeps running while the dryer is serviced.
Compatible Dryer Models
DP100 is for Castair refrigerated dryers at RD71-15K and larger:
- RD71-15K: 71 CFM @ 37°F dew point, 1" NPT, 115V/1ph, 7.5A, 110 lbs, 11.8x23.7x22.8"
- RD113-60K: 107 CFM @ 37°F dew point, 1" NPT, 115V/1ph, 9.0A, 119 lbs, 11.4x30.5x24.5"
- RD161-37K: 161 CFM @ 37°F dew point, 1.5" NPT, 115V/1ph, 11.4A, 137 lbs, 11.4x33.7x24.5"
For dryers smaller than the RD71-15K (RD25-6K or RD59-11K), use the DM75 or DM75E compressor-mounted kit instead.
What's Included with DP100
- 3-ball valve bypass assembly — allows dryer to be isolated from the air system for service
- Plumbing fittings for connection to dryer
Note: The DP100 is a bypass/plumbing kit only. The dryer, compressor, and all other system components are sold separately. Exact component list and dimensions for the DP100 are not published in Castair's public specifications — contact us to confirm what's included and verify compatibility with your installation before ordering.
How the Bypass Works
The 3-ball valve bypass configuration in the DP100 follows standard compressed air installation practice:
- Normal operation: Air flows from the compressor through the inlet isolation valve, through the dryer, and out the outlet isolation valve into the distribution system. The bypass valve is closed.
- Dryer service mode: Close both dryer isolation valves, open the bypass valve. Air bypasses the dryer and flows directly to the distribution system. The dryer is now isolated and can be serviced, recharged, or replaced with the compressor still running.
- This is required for any production environment where compressed air cannot be interrupted for dryer maintenance.
Sizing Your Dryer for the Compressor
Dryer capacity is rated at 100°F inlet air, 100°F ambient, at 100 psi. If your compressor discharges at higher temperatures — which is common at the compressor outlet before an aftercooler — capacity is derated. At 150°F inlet air, capacity drops to 55% of the rated CFM. For a 71 CFM dryer, that means 39 CFM effective capacity at 150°F inlet. Size your dryer based on your actual inlet temperature, not just your compressor's total CFM output.
Why Buy From Air Compressor Factory Direct?
- Specialist since 2016 — we stock Castair dryers and plumbing accessories and can help design your installation
- Free shipping on qualifying orders
- Free tech support at 866-217-0063 — call us to confirm the right bypass kit and dryer size for your compressor
- Full manufacturer warranty on all Castair equipment
- Honest guidance — if you need the DM75 instead (for a smaller dryer), we'll tell you
Call 866-217-0063 for quick answers and help!
