The Castair RDD40SV is the solenoid valve replacement part for the RDD40 refrigerated compressed air dryer. The automatic demand drain on a Castair refrigerated dryer is controlled by a solenoid valve — it opens to eject condensate when liquid is detected and closes immediately after, without bleeding compressed air unnecessarily. When this solenoid fails, the dryer either loses its automatic drain function entirely (moisture starts passing through) or the drain stays open continuously (constant air loss and noise). The RDD40SV replaces that solenoid valve directly.
This is a standard service part for RDD40 series dryers in regular shop service. Solenoid valves wear out — coil insulation breaks down over time, the plunger develops wear, or internal seals fail. In high-cycle environments where the compressor runs frequently and the dryer drain is operating dozens of times per hour, solenoid replacement every few years is normal maintenance, not a failure event.
Symptoms of a Failed Drain Solenoid
- Continuous air bleed from the drain: Solenoid is stuck open — valve plunger or seat is worn, or the coil is shorted. Replace the solenoid valve.
- No drainage, moisture at tools: Solenoid is stuck closed — coil burned out or plunger seized. The dryer is chilling the air but cannot eject the condensate, so it re-evaporates back into the airstream downstream.
- Intermittent drainage: Coil is marginal, plunger is sluggish — replace before it fails completely.
- Solenoid buzzing or overheating: Coil failure in progress. Replace immediately.
Key Features
- Direct replacement: OEM Castair solenoid valve for the RDD40 dryer drain circuit
- Demand-drain design: Valve only opens when condensate is detected — conserves compressed air vs. timer-based drains
- Application-specific: Matched to the RDD40 drain circuit voltage and flow requirements
What's in the Box
- Castair RDD40SV replacement solenoid valve for RDD40 refrigerated dryer
Note: Installation requires basic electrical and pneumatic disassembly skills. Depressurize the dryer and disconnect power before replacing. Contact us at 866-217-0063 for installation guidance.
Compatible Equipment
- Castair RDD40 series refrigerated compressed air dryers
- Confirm with your unit model and serial number — call 866-217-0063 before ordering if unsure
Technical Specifications
- Part Number: RDD40SV
- Manufacturer: Castair (Cast Air, Inc.)
- Application: Castair RDD40 refrigerated compressed air dryer, drain circuit
- Component type: Solenoid valve
- Electrical specifications: Contact us for coil voltage and wiring details — 866-217-0063
Why Buy From Air Compressor Factory Direct?
We carry Castair service parts and can help you identify the correct solenoid for your RDD40 dryer. If you are troubleshooting a drain problem and are not certain which component has failed, call us before ordering — we can walk through the diagnosis with you. Free shipping on qualifying orders, free pre-sale technical support, genuine Castair parts.
Call 866-217-0063 for quick answers and help!
