a turbine wheel and gear system rotate an output shaft in response to flow , where the output shaft is connected to a clutch cup that engages a clutch and valve disk . the disk cooperates with a valve seat formed on a piston to permit / prevent flow within the piston . during flow , the clutch clamps to the disk , and the piston and disk move downstream until an associated control member hits a stop , opening the valve , while the piston continues downstream . the clutch rotates the disk and control member , and if a maximum flow volume occurs , the control member rotates to an interrupt position and is released from the stop , closing the valve . passages allow restricted flow to disengage the clutch and permit a spring to move the piston and valve upstream until engaging a reset cam that rotates the control member back to an initial position .