A valve of this class has become known from German Utility Patent No. DE-GM 84 25 137. This prior-art valve has valve bodies arranged in the same direction in a valve housing at a connecting rod, and these valve bodies come to lie on flange-like valve seats in the valve housing in the closed position in the same direction. Elastomeric sealing rings, which seal the flow channels leading from the interior space of the valve housing to the outside via the valve seats in the closed position of the valve bodies, are provided between the valve seats and the valve bodies.
It is disadvantageous in the prior-art valve that tolerances of the double fit between the valve bodies and the corresponding valve seats can be compensated only partially via the elasticity of the sealing rings in the closed position. It may happen due to the rigid coupling of the valve bodies via the connecting rod that even though a valve body is in contact with the valve seat belonging to it, a leakage flow develops between the other valve body and the valve seat. This leakage flow can be stopped only via a closing force of corresponding strength acting on the valve bodies.
A demand oxygen system, which has a valve body on a valve seat in a valve housing and a compensation piston rigidly connected to the valve body for admission pressure compensation, has become known from Swiss Patent No. CH-PS 466 051. A control lever, which is in contact with a control diaphragm of the demand oxygen system, is mounted in the valve housing in an articulated manner, and it actuates the compensation piston and the valve body during a deflection of the control diaphragm, as a result of which pressurized gas can flow into the control diaphragm space formed by the control diaphragm and the inner space of the valve housing.
It is disadvantageous in the prior-art metering valve that a substantial static friction must be overcome during the actuation of the compensation piston, because the compensation piston is accommodated axially displaceably in a hole of the valve housing with an O-ring seal. The static friction leads to reduced sensitivity of response of the demand oxygen system. Even though it would be possible to compensate the static friction to a certain extent by a larger control diaphragm, doing so would considerably interfere with the ease of handling of the demand oxygen system.