Found this one that was suggested for perfect application.
Designed for use where space is limited. May be installed in trouble spots previously neglected or improperly vented.
The valve is always in a closed position until the air collects in the valve shell. When sufficient air accumulates to replace the waer, the float drops and the float lever pulls downward on the self-closing valve, unseating it. As the air passes out of the vent, liquid again fills the valve shell which raises the float, causing the valve to seat once again. As fast as air accumulates, this action is repeated.
For use on systems with pressures up to 50 pounds.
No air chamber required.
size: 2 5/8inches x 1 1/2inches
Bright brass finish.