Diaphragm size - Dwyer® Pressure Switches are offered in three series based on diaphragm size. Series 1600 models have a 7-3/4" diaphragm diameter which provides the greatest actuating force for maximum sensitivity and repetitive accuracy. Series 1800 models with 4" diaphragms are compact and low in cost, yet they deliver excellent performance for OEM and general service. Series 1900 models have 3-1/2" diaphragms operating through Dwyer-engineered force-motion amplifier levers, assuring high sensitivity and repeatability in these compact, low cost switches.