GILLIG LOW FLOOR, Руководство по обслуживанию

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233
Air System
Brake Relay Valve (Bendix R-4)
The parking brake relay valve (Figure 6-35) re-
ceives air from the brake treadle valve and sends
air (at the same pressure and higher volume) to the
rear spring brake chambers. This speeds up the ap-
plication and release of the brakes.
Operation
Application
Air pressure delivered to the service port enters the
small cavity above the piston and moves the piston
down. The exhaust seat moves down with the pis-
ton and seats on the inner or exhaust portion of the
inlet/exhaust valve, sealing off the exhaust passage.
At the same time, the outer or inlet portion of the
inlet/exhaust valve moves off its seat, permitting
supply air to flow from the reservoir, past the open
inlet valve, and into the brake chambers.
balance
The air pressure being delivered by the open inlet valve is also effective on the bottom area of the relay
piston. When air pressure beneath the piston equals the service air pressure above, the piston lifts slight -
ly and the inlet spring returns the inlet valve to its seat. The exhaust remains closed as the service line
pressure balances the delivery pressure. As delivered air pressure is changed, the valve reacts instantly to
the change, holding the brake application at that level.
exhaust or release
When air pressure is released from the service port and air pressure in the cavity above the relay piston
is exhausted, air pressure beneath the piston lifts the relay piston and the exhaust seat moves away from
the exhaust valve, opening the exhaust passage. With the exhaust passage open, the air pressure in the
brake chambers is then permitted to exhaust through the exhaust port, releasing the brakes.
Anti-compounding
The anti-compounding feature prevents strain on the brake components caused by application of the ser-
vice brakes while the parking brake is applied. To use this feature, the exhaust cover of the quick release
portion of the R-14 is removed and a line connected to the delivery of the R-12DC relay valve. With no
air pressure at the service port of the R-14, the parking brake is applied. If a service brake application is
made, air from the service brake valve enters the exhaust port of the R-14’s quick release and moves the
diaphragm, blocking the service port. Air then proceeds into the cavity above the relay piston, forces the
piston down, closing the exhaust and opening the inlet to deliver air to the spring brake cavity.
Exhaust
Cover
Exhaust
Seat
Exhaust
Port
Diaphragm
Inlet/Exhaust
Valve Assembly
Balance/quick Exhaust
Port (Anti-compound)
Piston Relay
Retaining Ring
Figure 6-35, R-14 Relay Valve