Parking brake system

In a vehicle having a normally spring applied, fluid pressure releasable brake (130), a brake pressure line (133), a brake exhaust line (138), a fluid pressure supply line (134), a fluid reservoir return line (136), a manual pump (166) having an inlet line (184) communicating with the fluid reservoir line (136) and an outlet line (180), the improvement comprising:

• a valve (140) including:
• a first port (154) in communication with the fluid pressure supply line (134);
• a second port (146) in communication with the brake pressure line (133);
• a third port (148) in communication with the manual pump outlet line (180);
• a fourth port (150) in communication with the brake exhaust line (138);
• a fifth port (152) in communication with the fluid reservoir return line (136);
• a restrictive orifice (192) communicating the second (146) and third (148) ports;
• and
• a valve element (156) selectively movable between first (5), second (8), and third (6) positions, the valve element (156) including means (160, 162) for communicating the first port (154) with the second port (146) and the third port (148) with the fourth port (150) for communication of fluid supply line pressure to the brake (130) for normal operation thereof when the valve element (156) is in said first position (5), for communicating the first port (154) with the fifth port (152) and the third port (148) with the second port (146) for manual pressurization of the brakes (130) when the valve element (156) is in said second position (8), and for communicating the first port (154) with the third port (148) and the fourth port (150) with the fifth port (152) for bleeding of the brakes (130) when the valve element (156) is in said third position (6).