Mid-West Instrument”sModel 121 indicating differential-pressure switch is a heavy–dutyversion of the Model 120, featuring the same rugged, field-provenpiston/housing design. In addition, the switch has aheavy-duty, industrial-type terminal strip for either one or twoswitches. Wiring can be performed with 1/2″ NPT conduit interface and a removable cover. A variety ofswitching configurations is available with one or two hermeticallysealed switches in SPST, SPDT configuration with 240 V, three W, or 60W ratings. The switch isavailable in aluminum or 316 SS pressure housing with 316 SS andceramic internal parts.  Safe working pressure is 6,000 PSIG (zero to 400bar). Differential pressure rangesfrom zero to five PSID (zero to .3 bar) to zero to 110 PSID (zero to 7 bar) with +/- 2 percentaccuracy. The weather-resistant gauge front is of reinforcedengineered plastic for corrosion resistance.