Fluid flow indicators

1,124,012. Fluid-flow indicator. BRITISH OXYGEN CO. Ltd. Jan. 11, 1966 [Oct. 12, 1964], No.41539/64. Heading G1R. A fluid-flow indicator for insertion in a pipeline system comprises a main valve 8 having a valve member 11 movable between an open position in which it offers only a small resistance to the flow of fluid through the valve in one direction, and a closed position in which it offers a large or infinite resistance to flow through it in the opposite direction, and means 10 not controlled by the valve member for indicating when the pressure on the downstream side of the valve member when in its closed position is less than the pressure on its upstream side by more than a chosen amount giving an indication of fluid-flow or halt of fluid-flow. The flow indicating device shown Fig. 3 comprises a valve member 24 having ports 38 and biased against valve seat 25 by spring 26 with passages 28, 29 leading off the main flow channel 23 on either side of the valve. The passages apply pressure to the outer sides of two diaphragms 30, 31 which enclose a chamber 32 having a pressure responsive electric switch to give a signal when there is a difference in pressure between the two channels 28, 29. The device may be used in breathing apparatus.