Gas flow indicator having a magnetic field sensitive switch that _is responsive to the position of a magnet secured to a piston

A gas flow indicator, comprising

• a cylinder having an input aperture and an output aperture and defining a generally cylindrical inner chamber between the apertures;
• a cylindrical piston constrained within the inner chamber for movement between the input aperture and the output aperture, whereby gas flowing in through the input aperture and out the output aperture goes around the piston and also forces the piston toward the output aperture;
• a spring positioned between the piston and the output aperture for forcing the piston away from the output aperture;
• a magnet secured to the piston;
• and
• a magnetic field sensitive switch positioned on the outside of the cylinder for being closed by the magnetic field of the magnet upon movement of the piston within the cylinder to a predetermined position dependent upon a predetermined force of gas flow in through the input aperture;
• whereby an indication of the state of gas flow through the cylinder may be provided in accordance with whether the switch is open or closed;
• wherein the inside diameter of the inner chamber in the region adjacent the input aperture is only slightly larger than the outside diameter of the piston so that gas flowing in through the input aperture forces the piston toward the output aperture end of the inner chamber and flows around and by the outside of the piston in said slightly larger diameter region;
• and
• wherein the inside diameter of the inner chamber in the region adjacent the output aperture is substantially larger than the outside diameter of the piston, with the transition in the size of the diameter of the inner chamber being defined by a step adjacent a position occupied by the piston notwithstanding how close the piston is to the output aperture, to thereby decrease the rate at which the piston is moved toward the output aperture in response to the flow of the gas as the rate of gas flow is increased while maintaining continued movement of the piston toward the output aperture, and to thereby damp variations in piston movement at the endpoint of a movement of the piston to a position of equilibrium determined by the rate of gas flow.