Bendix Commercial Vehicle Systems R-8P PRESSURE EQUALIZING PILOTRELAY - Manual (Page 2)

2
FIGURE 2 - OPERATIONAL VIEW OF APPLICATION FIGURE 3 - OPERATIONAL VIEW OF BALANCED POSITION
BALANCE (FIG. 3)
The air pressure being delivered by the open inlet valve also
is effective on the bottom area of the R-8P
™ valve relay piston.
When air pressure beneath the piston equals the service air
pressure on top of the piston, the piston lifts slightly and the
inlet/exhaust valve is returned to the inlet seat. The exhaust
remains closed as the delivery pressure balances with the
service line pressure. Balancing of the pressure above and
below the piston through the orifice of the R-8P
™ valve piston
assures that the service and delivery pressures are equal
and 0 p.s.i. differential exists. As delivered air pressure to
the R-8P
™ valve service port is changed, the valve reacts,
holding the desired application pressure.
EXHAUST OR RELEASE (FIG. 4)
When air pressure is released from the service port and air
pressure in the cavity above the piston of the R-8P
™ valve is
exhausted, air pressure beneath the piston lifts it upward,
further seating the inlet/exhaust valve against the inlet seat.
Raising the exhaust seat of the piston off the inlet/exhaust
valve, opens the exhaust. This allows the delivery air pressure
to rapidly exhaust to atmosphere. As air pressure under the
piston drops, the spring force above the piston will push the
piston downward, once again placing the exhaust seat of
the piston in contact with the inlet/exhaust valve. Any pressure
remaining under the piston will pass through the piston orifice
and be exhausted at the brake valve.
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 first, 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.
PISTON
ORIFICE
R-8P ™
VALVE
PISTON
RESERVOIR
INLET/EXHAUST
VALVE ASSEMBLY
BRAKE
VALVE SPRING
DELIVERY
VENT
RELAY
VALVE
SERVICE
BRAKES
SERVICE
SUPPLY
PISTON
ORIFICE
R-8P ™
VALVE
PISTON
RESERVOIR
INLET/EXHAUST
VALVE ASSEMBLY
BRAKE
VALVE SPRING
DELIVERY
VENT
RELAY
VALVE
SERVICE
BRAKES
SERVICE
SUPPLY
EXHAUST
FIGURE 4 - OPERATIONAL VIEW OF RELEASE
PISTON
ORIFICE
R-8P ™
VALVE
PISTON
RESERVOIR
INLET/EXHAUST
VALVE ASSEMBLY
BRAKE
VALVE SPRING
DELIVERY
RELAY
VALVE
SERVICE
BRAKES
SERVICE
SUPPLY
EXHAUST