Flow sensor responsive to fluid within a range from above a predetermined minimum to below a predetermined maximum and nonresponsive to fluid flows beyond said range

Claim 1

A flow sensor responsive to fluid flows within a range from above a predetermined minimum to below a predetermined maximum to indicate that flow is within that range and that the minimum flow has been exceeded but nonresponsive to fluid flows below the predetermined minimum or above the predetermined maximum to avoid giving a false indication of fluid flow, comprising in combination: (1) a housing having an inlet and an outlet and a through flow fluid passage therebetween; (2) a flow responsive valve disposed across the fluid passage in a manner to control flow therebetween, comprising; (a) a valve seat; (b) a valve member movable towards and away from the valve seat and having opposed faces said member including means for receiving downstream fluid pressure on a downstream face, (c) bias means biasing the valve member into a normally closed position against the valve seat with a force resisting upstream fluid pressure against upstream valve face tending to bias the valve downstream; (d) said means for receiving downstream fluid pressure including a flow controlling orifice open to flow past the valve member between the housing inlet and outlet at all times; and (e) a first fluid flow passage downstream of the valve seat and in communication with fluid pressure through said orifice, said valve member including bore means for communicating said downstream fluid pressure to said first passage; (3) a differential pressure indicator having (a) cooperating actuating and indicating magnetic elements, the actuating element movable between a first position in which it retains the indicating element in a nonindicating position and a second position in which the indicating element can move into an indicating position; the actuating element having opposed pressure faces and being movable towards one of the two positions according to the pressure differential therebetween; (b) said first passage communicating fluid pressure to one of the actuating element pressure faces, and a second fluid passage communicating fluid pressure upstream of the valve member to the other pressure face; (c) bias means retaining the actuating element in a first position to retain the indicating element in a nonindicating position at pressure differentials thereacross up to a predetermined minimum; and at pressure differentials exceeding the minimum to move away from the indicating element and release it to signal the reaching of such minimum pressure differential; and (d) means in the second fluid passage delaying communication of fluid pressure therethrough to delay actuation of the actuating element.