BENDIX R-8P PRESSURE EQUALIZING PILOTRELAY User guide

SD-03-1061A

Bendix®R-8P™Pressure Equalizing Pilot Relay Valve

DELIVERY

PORTS

SUPPLY PORT

SPRING

FIGURE 1 - CUTAWAY AND EXTERNAL VIEW

VENT

PISTON

BODY

SERVICE

(CONTROL)

PORT

EXHAUST

INLET/EXHAUST

VALVEASSEMBLY

DESCRIPTION

The R-8P™pressure equalizing pilot relay valve is a device

designed to reinforce the control signal on long wheel base

towing trailers and converter dollies.

Unlike a standard relay valve which typically has a 4 p.s.i.

crack pressure and similar differential between control and

delivery, the R-8P™valve has a 0 p.s.i. differential.

On the converter dolly and long wheel base towing trailers,

the R-8P™valve reinforces the service brake application

signal without the differential found in standard relay valves.

The 0 p.s.i. differential of the R-8P™valve assures that all

trailer and dolly brakes will receive the same strength control

signal even during light brake applications.

By providing a balanced pressure signal to all trailer and

dolly brakes, the R-8P™valve helps achieve overall vehicle

brake balance and stability. The R-8P™valve also helps

improve brake lining wear balance on combination vehicles

by causing even the most distant brake to contribute its

share of braking effort.

OPERATION

APPLICATIONS (FIG. 2)

When a service brake application is made, air delivered from

the brake valve enters the service port of the R-8P™valve.

As air pressure fills the space above the piston, it begins to

force the piston down. Because of the spring force above

the piston, the piston exhaust seat is already in contact

with the inlet/exhaust valve, sealing off the exhaust. As the

piston begins to move downward it forces the inlet/exhaust

valve off the inlet seat, allowing air from the reservoir to be

delivered out the delivery ports of the R-8P™valve in direct

proportion to the pressure received at the service port.

Any differential between service and delivery pressure caused

by friction or resistance to the movement of the piston

(commonly called crack pressure and normally in the range

of 2 to 4 p.s.i.) is eliminated due to passage of air through

the orifice in the piston.

COVER

SUPPLY PORT

DELIVERY PORT

PISTON

ORIFICE

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

VALVEASSEMBLY

BRAKE

VALVE

SPRING

DELIVERY

VENT

RELAY

VALVE

SERVICE

BRAKES

SERVICE

SUPPLY

PISTON

ORIFICE

R-8P™

VALVE

PISTON

RESERVOIR

INLET/EXHAUST

VALVEASSEMBLY

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

VALVEASSEMBLY

BRAKE

VALVE

SPRING

DELIVERY

RELAY

VALVE

SERVICE

BRAKES

SERVICE

SUPPLY

EXHAUST

FIGURE 5 - SCHEMATIC OF TYPICAL DOLLY SYSTEM

CONTROL FROM

TOWING TRAILER

SUPPLY FROM

TOWING

TRAILER

S = SUPPLY

SUPPLY TO

SECOND TRAILER

RE-6™RELAY

EMERGENCY

VALVE

SV-1™

SYNCHRO VALVE

SC-1™SINGLE

CHECK VALVE

CONTROL TO

SECOND TRAILER

R-8P™

RELAY VALVE

OPERATION AND LEAKAGE TEST

1. Block the wheels and fully charge the air system. Adjust

the brakes.

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 exhaust of the R-8P™valve. 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-8P™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 is unable to pass

these operation and leakage tests, repair or replace it

with a new or genuine Bendix remanufactured unit,

available at any authorized parts outlet.

WARNING! PLEASE READ AND FOLLOW

THESE INSTRUCTIONS TO AVOID

PERSONAL INJURYOR DEATH:

When working on or around a vehicle, the following

general precautions should be observed at all times.

1. Park the vehicle on a level surface, apply the

parking brakes, and always block the wheels.

Always wear safety glasses.

2. Stop the engine and remove ignition key when

working under or around the vehicle. When

working in the engine compartment, the engine

should be shut off and the ignition key should be

removed. Where circumstances require that the

engine be in operation, EXTREME CAUTION should

be used to prevent personal injury resulting from

contact with moving, rotating, leaking, heated or

electrically charged components.

3. Do not attempt to install, remove, disassemble or

assemble a component until you have read and

thoroughly understand the recommended

procedures. Use only the proper tools and observe

all precautions pertaining to use of those tools.

4. If the work is being performed on the vehicle’s air

brake system, or any auxiliary pressurized air

systems, make certain to drain the air pressure from

all reservoirs before beginning ANY work on the

vehicle. If the vehicle is equipped with an AD-IS™

air dryer system or a dryer reservoir module, be

sure to drain the purge reservoir.

5. Following the vehicle manufacturer’s

recommended procedures, deactivate the electrical

system in a manner that safely removes all

electrical power from the vehicle.

6. Never exceed manufacturer’s recommended

pressures.

7. Never connect or disconnect a hose or line

containing pressure; it may whip. Never remove a

component or plug unless you are certain all

system pressure has been depleted.

8. Use only genuine Bendix®replacement parts,

components and kits. Replacement hardware,

tubing, hose, fittings, etc. must be of equivalent

size, type and strength as original equipment and

be designed specifically for such applications and

systems.

C = CONTROL

D = DELIVERY

E = EXHAUST

EM = EMERGENCY

FIGURE 6 - CUTAWAY

9. Components with stripped threads or damaged

parts should be replaced rather than repaired. Do

not attempt repairs requiring machining or welding

unless specifically stated and approved by the

vehicle and component manufacturer.

10. Prior to returning the vehicle to service, make

certain all components and systems are restored

to their proper operating condition.

REMOVAL

1. Block or hold the vehicle by means other than the brakes.

2. Drain all air brake system reservoirs.

3. Identify, mark and disconnect all air lines from the R-8P™

pilot relay valve.

4. Remove the R-8P™valve from its mount on the vehicle.

DISASSEMBLY OF VALVE (REFER TO FIG. 6)

1. Note and mark position of valve cover (6) to body (7).

2. Remove four 5/16"-18 hex screws and separate the cover

from the body (7).

3. Remove and discard sealing ring (3) from body (7).

4. Remove piston (8) and spring (9) from cover (6) and retain

all parts.

5. Remove and discard o-ring (2) from piston (8).

6. Remove screw (11), washer (12) and diaphragm (5) from

exhaust cover (10). Discard diaphragm (5).

7. Remove four 10-24 screws which secure exhaust cover

(10) to body (7).

8. Remove and discard inlet exhaust assembly (4) from

body (7).

9. Clean all remaining parts in a cleaning solvent equivalent

to mineral spirits. Make certain all surfaces, bores and

passages are clean and dry.

ASSEMBLY (REFER TO FIG. 6)

NOTE: Make certain both piston orifices are open and not

clogged. Grease all o-rings, o-ring grooves and bores

with a barium base lubricant.

1. Install diaphragm (5) and diaphragm washer (12) and

secure with screw (11). Torque screw to 15-25 inch

pounds.

2. Install inlet and exhaust valve assembly (4) in valve body

(7). Position exhaust cover assembly (10) so that all

holes are properly aligned and secure with four 10-24

screws. Torque screw to 20-30 inch pounds.

3. Install sealing ring (3) in valve body (7).

4. Install o-rings (1 and 2) on the piston (8).

5. Install spring (9) in valve cover (6) so that the large

diameter end of the spring will rest on the piston.

6. Install piston (8) (with its o-rings installed) in valve cover

(6). Note: Make certain spring (9) is centered and not

binding.

7. Install valve cover (6) on valve body (7) in same position

as marked in Step 1 of “Disassembly”. Secure the cover

to the body using four 5/16" hex head cap screws. Torque

to 120-150 inch pounds.

INSTALLATION

1. Mount the R-8P™valve to the vehicle using new bolts or

other hardware.

2. Connect air lines to the R-8P™valve using identification

made during Step 3 of “Removal” instructions.

3. Perform “Operation and Leakage Checks” before placing

vehicle in service.

SUPPLY

PORT

10 511 12 EXHAUST

DELIVERY PORTS

VENT

SERVICE

(CONTROL)

PORT

PISTON

ORIFICE

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