M1 and M4 differences
9013 Pressure switch
The M4 form is for a Low pressure cut off, the contacts will open at 10 psi below the set cut in pressure. This is used to protect pipe from low pressure collapse in boost pump applications, and pumps running dry in low flow conditions. The M1 form is for a Maintained manual cut-out lever, the switch will stay off when lever is manually set in the off position. The lever will then need to be reset manually to start the operation again. It is primarily used during extended shutdowns.