Sectional Views; Application/Exhaust Or Release; Anti-Compounding; Operation - BENDIX R-12-R-14 RELAY VALVES Manual

EXHAUST
SEAT
EXHAUST
PORT
FIGURE 2 - SECTIONAL VIEWS
All parts are interchangeable between the R-12
valves with the exception of the detail components of the
™
R-14 valve 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 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.
2
RELAY
PISTON
INLET/
EXHAUST
ASSEMBLY
RETAINING
RING
R-12V
™ and R-14
EXHAUST COVER
EXHAUST
SEAT
RETAINING
RING
™
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 (SIMULTANEOUS
SERVICE AND PARK APPLICATION)
In those applications where the R-14
control spring brake chambers, the anti-compound feature
may be utilized. With the anti-compound feature of the
™
R-14 valve 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
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 valve, 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 valve 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 as described
under the section of this manual entitled Application.
PREVENTIVE MAINTENANCE
Important: Review the Bendix Warranty Policy before
performing any intrusive maintenance procedures. A warranty
may be voided if intrusive maintenance is performed during
the warranty period.
BALANCE/QUICK EXHAUST PORT
(ANTI-COMPOUND)
DIAPHRAGM
RELAY
PISTON
INLET
EXHAUST
VALVE
ASSEMBLY
EXHAUST
PORT
R-14H
™
relay valve is used to
™
valve is removed and a line is