Bendix Commercial Vehicle Systems R-12P PILOT RELAY VALVE 4/11 - Manual (Page 5)

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FIGURE 9 - REDUCTION OF SUPPLY PRESSURE
LOAD PISTON
INLET/EXHAUST
VALVE
CONTROL
PORT
DELIVERY PORT
SUPPLY PORT
RELAY PISTON
RESERVE SPRING
SEALS EXHAUST
EQUALIZING (SLOW) EXHAUST (SEE FIGURE 8)
As described earlier, the result of any service brake
application with a Bendix
® R-12P ™ valve is air pressure
balance above and below the relay piston. If the brake
valve is modulated slowly upon release so that pressure
beneath the piston is not great enough to open the exhaust,
delivery air will pass through the equalizing orifi ce and out
the control port to be exhausted.
REDUCTION OF SUPPLY PRESSURE
Figure 9 shows the R-12P ™ valve with no supply pressure.
With no supply air, the reserve spring is strong enough
to hold the relay piston on the exhaust seat, but it is not
strong enough to overcome the force of the inlet/exhaust
valve spring. So both inlet and exhaust valves are closed.
Service Brake Applications with Reduced Supply
Pressure
Rapid Application - Use of Supply Line Single Check
Valve
If a rapid service brake application is made, control air
moves the relay piston and opens the inlet valve; but there
is no supply air to deliver. Control air then travels into the
supply port. The single check valve in the R-12P
™ valve
supply port (shown in Figure 2) prevents this air from
escaping to atmosphere through the open or damaged
supply source. Control air also passes through the
equalizing orifi ce and out the delivery port, assuring no
reduction or loss of control signal to subsequent vehicles.
Equalizing (Slow) Application
If an equalizing (slow) service brake application is made
with reduced supply air pressure, control air passes
through the equalizing orifi ce and out the delivery port to
subsequent vehicles in the train.
Control air cannot escape to atmosphere because the
reserve spring keeps the exhaust closed.
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.
No two vehicles operate under identical conditions, as a
result, maintenance intervals may vary. Experience is a
valuable guide in determining the best maintenance interval
for air brake system components. At a minimum, the valve
should be inspected every 6 months or 1500 operating
hours, whichever comes fi rst, for proper operation. Should
the valve not meet the elements of the operational tests
noted in this document, further investigation and service
of the valve may be required.
SERVICE CHECKS
1. Remove any accumulated contaminants. Visually
inspect the valve’s exterior for excessive corrosion
or physical damage. Repair/replace the valve as
necessary.
2. Inspect all air lines connected to the valve for signs
of wear or physical damage. Repair/replace as
necessary.
3. Test air line fi ttings for excessive leakage and tighten
or replace as necessary.
OPERATIONAL AND LEAKAGE TESTS
1. Block the vehicle’s wheels and fully charge the air
system.
2. Apply and release the service brakes several times
and check for prompt response of the brakes at all
appropriate wheels.
3. With the air system fully charged, apply a soap solution
to the R-12P ™ valve exhaust port. Leakage of a 1”
bubble in 5 seconds is permissible.
4. Make and hold a full brake application and again apply
a soap solution to the R-12P ™ valve exhaust. Leakage
of a 1” bubble in 3 seconds is permissible.
5. With the brakes still applied, apply a soap solution
around the valve where the cover meets the body. No
leakage at this point is permitted.
If the valve does not function as described; or if leakage is
excessive, repair the valve or replace it at any authorized
parts outlet.