101/121 Differential Pressure Switch

101/121 differential pressure switches are rugged, field-mounted instruments that incorporate a flexible modular design providing cost effective sensing solutions. The two-piece piston design allows for complete differential pressure reversal without damage. Process pressure is sensed by a diaphragm-piston combination. Hi-side system pressure acts on the piston to product force Fh. It is counteracted by the adjustable range spring force Fs and Lo-side system pressure acting on the backside of the piston to produce force Fl. The resultant force Fd acts on the piston and overcomes the force of the adjustable range spring [Fd= Fh – (Fl + Fs)] and moves a shaft that actuates (deactuates) an electrical switching element.