Low pressure selector

Low pressure selector apparatus adapted for connection to at least two sources of pneumatic pressure, comprising:

• a housing, including first, second and third ports and a cavity formed by walls therein, said second and third ports being adapted for connection to such pneumatic sources, respectively, said cavity including a first wall forming a first cavity portion of a first cross section and second and third walls forming second and third cavity portions at least including segments of greater cross section than said first portion, said second and third cavity portions adjoining opposite ends of said first cavity portion, said first, second and third ports communicating with said first, second and third cavity portions, respectively;
• a piston mounted for reciprocating movement within said cavity between first and second positions in response to pressure appearing at said second and third ports, a drop in pressure appearing at said third port relative to pressure appearing at said second port causing said piston to move to said first position and a drop in pressure appearing at said second port relative to pressure appearing at said third port causing said piston to move to said second position, said piston including first and second surface portions at its respective ends and a third surface portion disposed between said first and second surface portions and including an annular depression circumferentially about said piston for communicating pressure about said piston to access said first port;
• first and second sealing members mounted on said first and second surface portions of said piston, at least one of said first and second sealing members being disposed to slidably engage said first wall of said cavity to at least partially define the axis of movement of said piston, said first sealing member being disposed to be in sealing engagement with said first wall when said piston is in said first position to prevent communication between said first port and said second port, and said second sealing member being disposed to be in sealing engagement with said first wall when said piston is in said second position to prevent communication between said first port and said third port, said sealing members being mutually disposed for sealing engagement of only one of said sealing members with said first wall at least when said piston is in said first or second positions and for cooperation with said second and third walls to permit communication between said first port and said third port when said piston is in said first position and to permit communication between said first port and said second port when said piston is in said second position.

Low pressure indicator apparatus for monitoring at least two sources of supply pressure in a vehicle pneumatic brake system, comprising:

• a housing, including a cavity formed by walls therein and first, second and third ports, said second and third ports being adapted for connection to said sources of supply pressure and all of said ports communicating with said cavity;
• piston means mounted for reciprocating movement within said cavity between first and second positions in response to pressure appearing at said second and third ports, a drop in pressure appearing at said third port relative to pressure appearing at said second port causing said piston means to move to said first position and a drop in pressure appearing at said second port relative to pressure appearing at said third port causing said piston means to move to said second position, said piston means including sealing means for cooperation with said walls forming said cavity to permit communication between said first port and said third port and prevent communication between said first port and said second port when said piston means is in said first position and to permit communication between said first port and said second port and prevent communication between said first port and said third port when said piston means is in said second position;
• and
• pressure responsive monitoring means connected to said third port for signaling reduction in pressure appearing at said third port below a preset minimum.

Low pressure indicator apparatus for monitoring at least two sources of supply pressure in a vehicle pneumatic brake system, comprising:

• a housing, including first and second chambers formed by walls therein, a passage for providing communication between said first and second chambers and first and second ports adapted for connection to such sources of supply pressure, said first and second ports being in communication with said first chamber;
• first piston means mounted within said first chamber for reciprocating movement therein between first and second positions in response to pressure appearing at said first and second ports, a drop in pressure appearing at said second port relative to pressure appearing at said first port causing said first piston means to move to said first position and a drop in pressure appearing at said first port relative to pressure appearing at said second port causing said first piston means to move to said second position, said first piston means including sealing means for cooperation with said walls forming said first chamber to permit communication of pressure between said second port and said passage and prevent communication of pressure between said first port and said passage when said first piston means is in said first position and to permit communication of pressure between said first port and said passage and prevent communication of pressure between said second port and said passage when said first piston means is in said second position;
• second piston means mounted within said second chamber for reciprocating movement therein between first and second positions in response to pressure appearing at said passage;
• means for urging said second piston means to said second position;
• and
• flag means mounted on said housing for indicating when said second piston means is in said second position.

A vehicle pneumatic system including a low pressure selector, at least two sources of supply pressure and pressure responsive monitoring means, the low pressure selector comprising:

• a housing, including a cavity formed by walls therein and first, second and third ports, said first, second and third ports being adapted for connection respectively to said pressure responsive monitor means and said sources of supply pressure;
• piston means mounted for reciprocating movement within said cavity between first and second positions in response to pressure appearing at said second and third ports, a drop in pressure appearing at said third port relative to pressure appearing at said second port causing said piston means to move to said first position and a drop in pressure appearing at said second port relative to pressure appearing at said third port causing said piston means to move to said second position, said piston means including sealing means for cooperation with said walls forming said cavity to permit communication of pressure between said first port and said third port and prevent communication of pressure between said first port and said second port when said piston means is in said first position and to permit communication of pressure between said first port and second port and prevent communication of pressure between said first port and said third port when said piston means is in said second position.