Vent valve device having disabling means

A vent valve device for locally venting a railway car brake pipe when an emergency rate of reduction of the fluid pressure carried in said brake pipe is initiated, comprising:

• (a) a housing having an inlet port to which said brake pipe is connected, a vent port, a first chamber communicated with said inlet port, and a second chamber;
• (b) flow restrictor means between said first and second chambers for controlling the rate at which fluid pressure is released from said second chamber in response to a reduction of said brake pipe pressure to thereby establish a predetermined pressure differential between said first and second chambers when said brake pipe pressure is reduced at an emergency rate;
• (c) piston valve means for establishing fluid pressure communication between said inlet port and said vent port in accordance with said predetermined pressure differential being established between said first and second chambers;
• and
• (d) disabling means selectively operable to an actuated position for releasing fluid under pressure from said second chamber to prevent said predetermined pressure differential from being established between said first and second chamber, said disabling means being automatically resettable, from said actuated position to a de-actuated position in which the release of fluid pressure from said second chamber is cut-off, when fluid pressure in said second chamber is reduced below a predetermined value.