Gas by-pass valve

A microvalve for controlling the flow of a pressurized oxygen gas or other gas from a source of the gas to a user, the valve comprising a casing having wall means defining a valve chamber and a guide cylinder longitudinally adjoined along a central longitudinal axis, the valve chamber being larger than the guide cylinder in respective cross sections transverse to the longitudinal axis, the wall means comprising an annular shoulder in the casing at the joinder of the valve chamber and the guide cylinder and transverse to the longitudinal axis, at least one gas inlet port defined by the wall means fluidically connected to the valve chamber and at least one gas outlet port defined by the wall means, the shoulder defining a valve seat on an axis spaced from the central longitudinal axis and fluidically connected to the outlet port, a plunger slidably positioned in the valve chamber and selectively moveable within the valve chamber along the longitudinal axis toward and away from the shoulder, the plunger having a first end transverse to the longitudinal axis and operatively engaging the shoulder in a valve closed position, the plunger comprising means at the first end defining a peripheral groove, and a compressible O-ring defining a front annular surface mounted on the plunger peripheral groove for movement with the plunger between a valve-open position in which the O-ring is spaced from the valve seat to permit gas flow through the valve seat to the outlet port and the valve-closed position in which the front annular surface of the O-ring is compressed against the shoulder with only a portion of the front annular surface engaging the valve seat to close the valve seat and prevent gas flow through the valve seat to the outlet port, means for normally holding the plunger in one of the two positions, and actuating means for moving the plunger to the other of the two positions.