As will be apparent from the illustrations the complete flow switch comprising orifice plate, differential pressure sensitive element and switching mechanism are combined in a single compact assembly which enables easy installation between pipe flanges, models being available for pipe sizes 15 - 250 mm diameter. 

These sensors incorporate a spring loaded pressure sensitive flexible diaphragm, which when deflected by pressure drop across the orifice plate, actuates directly by push rod a snap action S.P.D.T. microswitch at the flow setting selected on the adjustment scale.

Each instrument can be provided with one of seven standard orifice ratios which enables a wide range of flow rates to be accommodated. When using fluids other than fresh water these values will of course alter. It should be also noted that the head loss values are those occurring immediately across the orifice and that up to 50% of this head loss can be recovered by providing at least ten diameters of straight plain pipe either side of flow switch. 

Each instrument is tested before despatch and switch set point marked on adjustment scale. If specially ordered this scale can be calibrated to indicate the adjustable range of flow rate in litres per hour or other units of measurement as required. The accuracy of such calibration will be affected by many external factors such as fluid temperature change, pipe layout etc., but experience has shown this to be within +/-5% for a given set of conditions.