Bendix R-7 MODULATING VALVE User Manual

®

Bendix® R-7™ Modulating Valve

SD-03-4504

	EXHAUST	CONTROL
		PORT		EXHAUST
		SUPPLY	INLET
	MOUNTING		VALVE
		PORT	SPRING	CONTROL
	HOLE (2)
				PORT
			INLET	CONTROL
	DELIVERY (2)		EXHAUST	PISTON
			VALVE	DOUBLE CHECK
			MOUNTING	VALVE(SUPPLY
				PORT & BALANCE
			SURFACE
	BALANCE			PORT)
			INLET
	PORT			SINGLE
			VALVE
			SEAT	CHECK
			BALANCE	VALVE

		PISTON
	MOUNTING	INNER SPRING	DELIVERY
			PORT (2)
	HOLE (2)
		SUPPLY
		OUTER SPRING	ADJUSTING SCREW

BALANCE

CONTROL

EXHAUST

FIGURE 1 - EXTERIOR & INVERTED VIEW

DESCRIPTION

The R-7™ modulating valve is used in conjunction with a dual air brake system and spring brake actuators, and performs four functions:

1.Limits hold-off pressure to the spring brake actuators (adjustable).

2.Provides for quick release of air pressure from the spring cavity of the spring brake actuator allowing a fast application of the spring brake actuators.

3.Modulates spring brake actuator application should a failure occur in the service brake system.

4.Prevents compounding of service and spring forces.

The valve has one 1/4" control, one 3/8" supply, one 1/4" balance, two 3/8" delivery NPTF ports, and an exhaust port protected by an exhaust diaphragm. The valve incorporates two 13/32" holes for mounting.

FIGURE 2 - SECTIONAL VIEW

Note for model year 2001 and later International Trucks only: There is an inverted R-7™ valve, which appears inverted from the other pictures in this document. A standard R-7™ valve and an inverted R-7™ valve are not interchangeable. See Figure 1 for a picture of an inverted R-7™ valve.

OPERATION - CHARGING SPRING BRAKE ACTUATORS (FIGURE 3)

Air pressure used to control the spring brake actuators enters the valve through the supply port, passing through one side of the double check valve, through the open inlet valve, over the balance piston, and out the delivery ports to the spring brake actuators. When air pressure in the spring brake actuator cavity has released the spring brake actuators and when air pressure on top of the balance piston is sufficient to overcome the force of the balance piston spring, the balance piston moves allowing the inlet valve spring to close the inlet valve, shutting off further air pressure from the reservoir supplying the modulating valve.

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			#1 RES.
SECONDARY SERVICE CIRCUIT
	EXHAUST		#2 RES.
CONTROL	PORT	CONTROL	DUAL BRAKE
PORT		PISTON	VALVE
			PRIMARY
			SERVICE
			CIRCUIT
			BALANCE
			PORT
			DOUBLE
			CHECKVALVE
SPRING			SUPPLY
BRAKE			PORT
ACTUATOR
INLET/EXHAUST		SINGLE	PARK
VALVE
		CHECK
			CONTROL
		VALVE
			VALVE
PRIMARY -		BALANCE PISTON
SECONDARY -

PARK -

+ SPRING BRAKE HOLD-OFF PRESSURE - SERVICE AIR PRESSURE

o ATMOSPHERE PRESSURE

FIGURE 3 - CHARGING

					#1 RES.
	SECONDARY		EXHAUST		#2 RES.
	SERVICE	CONTROL		CONTROL
	CIRCUIT		PORT
		PORT		PISTON	DUAL BRAKE
					VALVE
					PRIMARY SERVICE
					CIRCUIT
					BALANCE
					PORT
					DOUBLE
					CHECKVALVE

SPRING

BRAKE

ACTUATOR

INLET/EXHAUST

VALVE

PRIMARY -

SECONDARY -

PARK -

	SUPPLY
	PORT
SINGLE	PARK
CHECK	CONTROL
VALVE	VALVE

BALANCE PISTON

+ SPRING BRAKE HOLD-OFF PRESSURE - SERVICE AIR PRESSURE

o ATMOSPHERE PRESSURE

SECONDARY SERVICE CIRCUIT		#1 RES.
EXHAUST		#2 RES.
CONTROL PORT	CONTROL	DUAL BRAKE
PORT	PISTON
		VALVE
		PRIMARY SERVICE
		CIRCUIT
		BALANCE
		PORT
		DOUBLE
		CHECK
		VALVE
		SUPPLY
SPRING		PORT
BRAKE
ACTUATOR	SINGLE	PARK
	CHECK	CONTROL
INLET/EXHAUST	VALVE	VALVE
VALVE
PRIMARY -	BALANCE PISTON
SECONDARY -
PARK -

+ SPRING BRAKE HOLD-OFF PRESSURE - SERVICE AIR PRESSURE

o ATMOSPHERE PRESSURE

FIGURE 5 - SERVICE APPLICATION LOSS OF PRIMARY CIRCUIT

OPERATION - SERVICE APPLICATION WITH LOSS OF AIR IN PRIMARY CIRCUIT (FIGURE 5)

A service application made with a loss of air in the primary circuit would result in reduced air pressure delivered to the lower area of the control piston. Air pressure from the secondary circuit on top of the control piston would force the piston down, opening the exhaust valve and allowing air pressure in the spring cavity of the spring brake actuator to release and the spring brake actuator to apply the brakes.

The pressure differential between the primary and secondary circuits regulates the amount of air pressure released from the spring cavity of the spring brake actuator. This results in a total brake application on the rear axle which is proportionate to the braking on the other axles.

FIGURE 4 - NORMAL SERVICE APPLICATION

NOTE: The force of the spring below the balance piston is adjustable by an external screw on the modulating valve. This adjustment is normally made so that the inlet valve will close at a slightly greater pressure than the hold-off pressure of the spring brake actuator, but below maximum system pressure.

OPERATION - NORMAL SERVICE APPLICATION (FIGURE 4)

When a service application is made by actuating the dual brake valve, air from the primary circuit is delivered to the lower side of the control piston through the balance port, and air from the secondary circuit is delivered to the top of the control piston through the control port. Because air pressure from the primary and secondary circuits are not equal, there will be a slight movement of the control piston.

			#1 RES.
SECONDARY
SERVICE	EXHAUST		#2 RES.
CIRCUIT	PORT	CONTROL	DUAL BRAKE
CONTROL
PORT		PISTON	VALVE
			PRIMARY SERVICE
			CIRCUIT
			BALANCE PORT
			DOUBLE
			CHECKVALVE

SPRING

BRAKE

ACTUATOR INLET/EXHAUST VALVE

PRIMARY -

SECONDARY -

PARK -

SUPPLY

PORT

	SINGLE	PARK
		CONTROL
	CHECK
		VALVE
	VALVE
	BALANCE PISTON

+ SPRING BRAKE HOLD-OFF PRESSURE - SERVICE AIR PRESSURE

o ATMOSPHERE PRESSURE

FIGURE 6 - SERVICE APPLICATION LOSS OF SECONDARY CIRCUIT

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