The Castair PSL1X is a 95-125 PSI pressure switch with an integrated unloader valve. It is the standard replacement switch for belt-drive, single-phase piston compressors running in the standard shop pressure range. The unloader valve is the key feature — when the motor shuts off at 125 PSI, the unloader bleeds the residual pressure from the pump discharge line so the motor can restart at 95 PSI against a free-spinning pump. Without this function, a single-phase motor tries to start under load, which trips thermal overloads and burns start capacitors. The PSL1X at $39.85 is inexpensive insurance for a motor that costs much more to replace.
How the Unloader Works
When the switch opens at 125 PSI cut-out, it simultaneously opens the unloader valve. Air bleeds back from the discharge line through a small copper tube to the pump intake. This drops the pressure on the pump head to near-zero. When pressure falls to 95 PSI and the switch closes to restart the motor, the pump starts against atmospheric pressure on the discharge side rather than against 100+ PSI of trapped air. The motor accelerates to speed quickly, the check valve closes, and compression resumes normally. This cycle happens dozens of times per day on a busy shop compressor, and the unloader is what makes it reliable long-term.
Key Features
- Operating range: 95 PSI cut-in / 125 PSI cut-out
- Unloader valve: Integrated — bleeds head pressure at every shutdown cycle
- Corrosion resistant cover: Weather and moisture resistant for shop installation
- Easy to adjust: Differential and cut-out pressure field-adjustable
- UL/CSA listed: Commercial electrical safety listed
Configuration Options at 95-125 PSI
- PSL1 — No unloader ($36.31)
- PSL1X — With unloader, no on/off lever ($39.85) — this unit
- PSL1MIX — With unloader and on/off lever ($40.73)
- PSL4MIX — With unloader, on/off, and four-way valve
When Do You Need This vs. Stepping Up or Down?
The PSL1X is correct for any single-phase belt-drive compressor running 95-125 PSI without a built-in on/off lever on the existing switch. If your existing switch had an on/off lever, order the PSL1MIX instead. If you are running a 145-175 PSI system, this is the wrong range — order the PSH1X. If your system has a four-port manifold connection, check the PSL4MIX. For most single-phase shop compressors in the 95-125 PSI range, the PSL1X is the right standard replacement.
Technical Specifications
- Part Number: PSL1X
- Manufacturer: Castair (Cast Air)
- Pressure range: 95-125 PSI
- Unloader valve: Yes, integrated
- On/Off switch: No
- Certifications: UL/CSA listed
- Cover: Corrosion resistant
- Price: $39.85
What's in the Box
- 1x Castair PSL1X pressure switch with integrated unloader valve
Why Buy From Air Compressor Factory Direct?
We stock the complete Castair component lineup. The PSL1X is a direct OEM-equivalent replacement — not a generic aftermarket switch that may have different port sizing or wiring configuration. Free shipping on qualifying orders. Call our tech line if you need help confirming the right switch for your compressor.
Call 866-217-0063 for quick answers and help!
