The Castair PSL4MIX is the top-configuration pressure switch in the 95-125 PSI range. It includes an integrated unloader valve, a manual on/off lever, and a four-way valve port arrangement. This is the switch for duplex compressor setups, multi-head pump configurations, or any system where the unloader needs to vent to multiple points. If your system uses standard single-port plumbing, the PSL1X or PSL1MIX is the correct choice — the PSL4MIX is for systems specifically designed for four-way operation.
Four-Way Valve Configuration — What It Means in Practice
The four-way configuration provides additional unloader ports beyond the standard single-port PSL1X. On a duplex compressor running two pump heads from one shared tank and one pressure switch, the four-way allows both pump heads to unload simultaneously at shutdown. Both motors then restart unloaded on the next pressure cycle. This is critical on two-pump systems — if only one pump head unloads, the other motor starts against head pressure, burning through start capacitors on that side. The PSL4MIX solves this with a single switch that handles both unload paths.
Key Features
- Operating range: 95 PSI cut-in / 125 PSI cut-out
- Unloader valve: Included with four-way configuration
- On/Off lever: Manual lever for controlled shutdown
- Four-way valve ports: Multiple unloader connections for duplex or complex plumbing
- Corrosion resistant cover: Shop-grade protection
- UL/CSA listed: Commercial electrical safety certification
Full Lineup — 95-125 PSI Pressure Switches
- PSL1 — No unloader, no on/off
- PSL1X — With unloader, no on/off
- PSL1MIX — With unloader and on/off
- PSL4MIX — With unloader, on/off, and four-way valve (this unit)
High-pressure (145-175 PSI) equivalent is the PSH4MIX.
When Do You Need the PSL4MIX?
Order the PSL4MIX when your compressor has multiple pump heads sharing one pressure switch, or when the existing plumbing has a four-port manifold at the switch connection. If you are replacing a single-pump compressor switch, you are ordering more than you need — use the PSL1MIX. If you are not sure how many unloader ports your existing switch has, count the copper or brass tubes running from the switch body back to the pump heads. One tube means PSL1X or PSL1MIX; multiple tubes means PSL4MIX.
Technical Specifications
- Part Number: PSL4MIX
- Manufacturer: Castair (Cast Air)
- Pressure range: 95-125 PSI
- Unloader valve: Yes, four-way configuration
- On/Off switch: Yes, manual lever
- Certifications: UL/CSA listed
- Cover: Corrosion resistant
What's in the Box
- 1x Castair PSL4MIX pressure switch with four-way unloader valve and on/off lever
Why Buy From Air Compressor Factory Direct?
We stock specialty Castair components including the four-way switch configurations that most general suppliers do not carry. If you are building or servicing a duplex compressor system, call us — we can help you confirm the correct switch and verify availability. Free shipping on qualifying orders.
Call 866-217-0063 for quick answers and help!
