The flowing fluid may pass through both thevariable piston annulus and/or the bypass
valve. A pressure drop is created across thepiston due to the flow rate of the fluid.
Increasing differential pressure causes thepiston to move and compress the range
spring. When the piston magnet is carried farenough, the switch magnet is attracted and
the output snap switch is actuated. Theamount of bypass valve opening determines
the flow rate switching point.