PREVOST LE MIRAGE XLII BUS SHELLS, Руководство по обслуживанию

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to be conveniently used as either a service or spring brake
relay valve. An exhaust cover is installed that protects the
1/8" balance port when the R-14 anti-compound feature is
not in use.
All parts are interchangeable between the R-12 and R-14
with the exception of the detail components of the R-14
cover. Both valves make extensive use of non-metallic
internal components. For ease of servicing, the inlet/
exhaust valve can be replaced without the need for line
removal.
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 piston 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
also is effective on the bottom area of the relay piston.
When air pressure beneath the piston equals the service
air pressure above, the piston lifts slightly and the inlet
spring returns the inlet valve to its seat. The exhaust re-
mains 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 ex-
hausted, 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, re-
leasing the brakes.
ANTI COMPOUNDING (SIMULTANEOUS
SERVICE AND PARK APPLICATION)
In those applications where the R-14 Relay Valve is used
to control spring brake chambers, the anti-compound
feature may be utilized. With the anti-compound feature
of the R-14 connected, a service application made while
the vehicle is parked is countered by a release of the
parking brakes. To utilize this feature, the exhaust cover
of the quick release portion of the R-14 is removed and a
line is installed which is connected to the delivery of the
service brake valve or relay valve. With no air pressure at
the service port of the R-14, the parking brakes are applied.
If a service brake application is made, air from the service
brake valve enters the exhaust port of the quick release of
the R-14 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
INLET/
EXHAUST
ASSEMBLY
EXHAUST COVER
FIGURE 2 - SECTIONAL VIEWS
RELAY
PISTON
INLET
EXHAUST
VALVE
ASSEMBLY
R-14H
R-12V
RETAINING
RING
EXHAUST
SEAT
RELAY
PISTON
EXHAUST
SEAT
RETAINING
RING
EXHAUST
PORT
DIAPHRAGM
BALANCE/QUICK EXHAUST PORT
(ANTI-COMPOUND)
EXHAUST
PORT