FLUID PRESSURE CONTROL VALVE DEVICE ARRANGED FOR FAIL-SAFE OPERATION

摘要

FLUID PRESSURE CONTROL VALVE DEVICE ARRANGED FOR FAIL-SAFE OPERATION In a proportioning type control valve device in which a piston valve assemblage is actuated to service position in accordance with a differential between brake pipe and control reservoir pressures on opposite sides of an actuating piston abutment forming a part of the piston valve assemblage, there is provided on the control reservoir side of the piston abutment a bellows device that is normally held under compression by the presence of control reservoir fluid pressure so as to be normally disengaged from the piston and engageable therewith only in the absence of control reservoir pressure to serve as the reference against which reductions in brake pipe pressure are measured to establish the actuating force on the piston abutment. When disengaged from the piston abutment under the influence of the control reservoir pressure, the bellows holds a control spring housed within the bellows under compression. This control spring acts through the bellows to provide the desired reference force on the piston abutment in the absence of sufficient control reservoir pressure to hold the bellows under compression.