Lefoo Air Compressor Pressure Switch with Unloader, 1 and 4 Port, 95/125 and 140/175 PSI

A pressure switch is what makes a compressor a compressor instead of a pump with a motor on it. It cuts motor power at the cut-out pressure, restores it at cut-in, and the built-in unloader bleeds head pressure off the discharge line each time it stops so the motor restarts against no load. If your compressor trips its breaker on restart, hums and will not turn over, or never shuts off, the switch and its unloader are the first two things to check. These are the Lefoo LF10 and LF17 switches, the series that replaces most single-phase reciprocating compressor controls.

Models and ratings

• LF10-1H-125 (U1128), 95/125 PSI factory setting, adjustable 35 to 150 PSI, 30 to 40 PSI differential, 1 port, 20 A, 1/4 in. FPT, unloader with 1/4 in. fitting, auto/off lever
• LF10-4H-125 (U1120), 95/125 PSI factory setting, adjustable 35 to 150 PSI, 30 to 40 PSI differential, 4 port, 20 A, 1/4 in. FPT, unloader with 1/4 in. fitting, auto/off lever
• LF10-L-4H-125 (U1140), 95/125 PSI factory setting, adjustable 35 to 150 PSI, 30 to 40 PSI differential, 4 port, 20 A, 1/4 in. FPT, UL listed, unloader with 1/4 in. fitting, auto/off lever
• LF10-L-4H-125 metric (U1142), same as above but with a 6 mm unloader fitting instead of 1/4 in.
• LF10-1H-175 (U1125), 140/175 PSI factory setting, adjustable 50 to 175 PSI, 30 to 50 PSI differential, 1 port, 20 A, 1/4 in. FPT, unloader with 1/4 in. fitting, auto/off lever
• LF10-4H-175 (U1126), 140/175 PSI factory setting, adjustable 50 to 175 PSI, 30 to 50 PSI differential, 4 port, 20 A, 1/4 in. FPT, unloader with 1/4 in. fitting
• LF17-1H-175 (U1130), 140/175 PSI factory setting, adjustable 40 to 250 PSI, 30 to 65 PSI differential, 1 port, 24 A, 1/4 in. FPT, unloader with 1/4 in. fitting

How to choose

Three things decide it. First, pressure range: match the switch to what the compressor is rated for, 95/125 for a standard shop machine and 140/175 for a high-pressure two-stage. Second, ports: a 1-port switch threads straight onto the tank, a 4-port manifold gives you tappings for the gauge, the safety relief valve and the discharge line so you are not building a tee assembly. Third, amperage: the switch has to carry the motor's full load current, so size it at or above the motor nameplate. The LF17 at 24 A covers motors the 20 A LF10 will not, and its 40 to 250 PSI adjustment range is the widest in the group.

Installation notes

Kill power at the breaker before touching the switch, and bleed the tank to zero before breaking the air connection. Transfer the unloader tube to the new switch in the same orientation, and seal the FPT port with thread sealant rated for air, not tape that can shed into the switch. After power-up, check the actual cut-in and cut-out against a gauge rather than trusting the factory setting, and adjust the range screw before touching the differential screw.

Typical applications

Single-phase reciprocating and piston compressors, portable and stationary shop units, twin-tank and wheelbarrow compressors, and as a replacement for worn Square D, Furnas and Condor controls where the electrical rating and port layout match.

Lefoo LF10 and LF17 air compressor pressure switches with integrated unloader, in 1 port and 4 port layouts, 95/125 PSI and 140/175 PSI, 20 A and 24 A, with 1/4 in. FPT tank connection.