Patent ID: 6121884
Filing Date: 2000-09-19
Classification: G01F,G01M,G01P

Abstract:
A gas flow detector (10) comprising a casing (12) having a gas inlet (14) and a gas outlet (16), a cylinder (24, 66) within said casing (12), a piston (38, 72) in said cylinder (24, 66), a flow path from said inlet (14) to a space below said piston (38, 76), a flow path from a space above said piston (38, 76) to said outlet (16), lifting of said piston from a lower position it occupies when there are equal gas pressures at said inlet and outlet to an upper position it occupies when the pressure at said outlet is lower than the pressure at said inlet, a magnet (44) carried by said piston at the lower end thereof and a magnetically operated switch (54) below the piston which is subjected to the field of said magnet (44) when said piston (38, 76) is in said lower position but not in the upper of said positions, characterized in that cylindrical surfaces of the piston (38, 76) and cylinder (24 66) seal said spaces off from one another whilst the piston is in its lower position, said cylindrical surfaces remaining in sealing contact during the initial part of the piston's upward travel in the cylinder, a flow path from said space below the piston to the space above the piston being opened only after the piston has completed said initial part of its upward travel.