Gas flow responsive signal output means

摘要

Signal output means (11) responsive to gas flow and particularly suited for use in gas flow indicator apparatus (10), has first and second pressure-datum valves (24, 25) arranged in downstream order in a gas conduit (16), the second pressure-datum valve (25) being arranged to open at a lower pressure difference than the first pressure-datum valve (24). A flueric amplifier (15) has a power jet port (28) connected to the gas conduit (16) on the upstream side of the first pressure-datum valve (24), opposed control pressure ports (26, 27) connected respectively to a chamber (22) formed between the first and second pressure-datum valves (24, 25) and to the gas conduit (16) downstream of the second pressure-datum valve (25), and a vent port (30) also connected to the gas conduit (16) downstream of the second pressure-datum valve (25). A pressure signal output by the flueric amplifier (15) in response to gas flow through the conduit (16) may be used to trigger a visual or audio warning device (14).