Fluid flow indicator

A gas flow indicator comprising:

• a housing defining a cylindrical flow passage having axially spaced first and second ends;
• gas supply means for supplying gas to said first end of said cylindrical passage;
• gas discharge means for discharging gas from the second end of said cylindrical passage;
• a cylindrical piston member having first and second terminal ends and an exterior diameter which is substantially less than the diameter of said passage, said piston member being axially positioned in said cylindrical passage with said first terminal end facing said first end of said passage and mounted for sliding movement from a first position adjacent said first end of said passage to a second position adjacent said second end of said passage when gas flow through said passage exceeds a predetermined level;
• a flow passageway extending through said piston member from an inlet adjacent the first terminal end to an outlet spaced axially from said first terminal end;
• said flow passageway including a flow control orifice therein;
• a metering ring formed circumferentially in said cylindrical flow passage and extending radially inwardly into closely spaced relationship with the exterior of said piston member, the location of said metering ring being such as to lie between said first terminal end of said piston member and said outlet of said flow passageway when said piston member is in said first position and between said first end of said cylindrical passage and said first terminal end of said piston member when said piston member is in said second position;
• and,
• means responsive to movement of said piston member from said first position to said second position for providing a signal exterior to said housing indicative of movement of said piston member.