Bendix Commercial Vehicle Systems PP-DC User Manual

Bendix® PP-DC® Park Control Valve

SD-03-3619

BUTTON

SUPPLY

FIGURE 1 - BENDIX® PP-DC® PARK CONTROL VALVE

EXHAUST

DELIVERY

SUPPLY

DESCRIPTION

The Bendix® PP-DC® park control valve is a push-pull, manually operable on/off valve. It is dash board-mounted and provides in-cab control of truck or bus parking brakes.

The valve is pressure sensitive—it automatically moves from the applied to the exhaust position when total system pressure drops below 20 to 40 psi. (Note that this is a Bendix mandated requirement. Refer to Bendix Technical Bulletin TCH-003-051). Also, manually pulling the button will apply the parking brakes.

The PP-DC valve body is made of non-metallic, noncorrosive material, and the cover is available in several variations (see Figure 1). The valve is designed to accept pipe thread ﬁ ttings or push-to-connect ﬁ ttings that use SAE J844 non-metallic air brake tubing.

Ports:

Port Embossed I.D. Primary Reservoir Supply SUP 11 Secondary Reservoir Supply SUP 12 Delivery DEL 21 Exhaust EXH 3

product specification and not a

BUTTON

COVER

EXHAUST

SUPPLY

EXHAUST

OPERATION

GENERAL

The PP-DC valve receives its supply of air from the primary service reservoir or the secondary service reservoir, whichever is at the higher pressure. When the button is pushed in, the valve delivers air to the spring brake chambers (usually through a spring brake valve such as the Bendix valve). The air releases the spring brakes for normal vehicle

operation.

To apply the parking brakes, the button is pulled out, which exhausts the PP-DC valve delivery and releases air from the spring brake chambers.

When total system pressure drops below 20 to 40 psi, the valve will automatically “pop out,” which removes the hold-off air in the chambers and applies the spring brakes.

PARKING BRAKES RELEASED

To release the parking brakes, the push-pull button is pushed in. The PP-DC valve plunger moves, closing the exhaust port with the exhaust seal and allowing the plunger o-ring to move past the guide spool. Supply air then travels out the delivery port to release the brakes.

SR-7® valve and a relay, or quick release,

Bendix®

ADB-22X

Disc Brake

Antilock

Modulator

(4 places)

Quick Release

Valve

™

Brake Valve

To Accessories

Air Dryer

Bendix

PP-DC®

Park Control

Valve

Bendix

PR-3™/ PR-4™

Valve

Bendix

EC-60

Controller

Front

Axle Reservoir

™

Electronic

Disc Brake

Service

Relay Valve

ADB-22X

™

Bendix

SR-7

Spring Brake

Modulating

Valve

Supply

Reservoir

Air Compressor

Air disc & drum brake actuation combined on a single axle are shown for pictorial purposes only.

FIGURE 2 - TYPICAL 4 X 2 TRUCK SCHEMATIC WITH BENDIX

Note that Figure 3 shows the primary service reservoir supplying the Bendix

PP-DC® valve. The double check valve diaphragm has sealed the secondary reservoir supply port and allows air to pass from the primary reservoir into the PP-DC valve.

If primary service reservoir pressure drops below secondary service reservoir pressure, the double check valve reacts as shown in Figure 4. It seals the primary service reservoir supply port and supplies the Bendix PP-DC park control valve with air from the secondary service reservoir. The push-pull button remains in and the spring brakes remain released.

PARKING BRAKES APPLIED

Figure 5 shows the PP-DC valve in the parking-brakesapplied position. This will occur when the driver manually pulls out the push-pull button, or when the total system pressure drops to below 20 to 40 psi.

As shown in Figure 6, when the button “pops” out, the exhaust seal moves to open the exhaust port to the atmosphere, allowing delivery line pressure to exhaust. The plunger o-ring moves to seal off supply pressure. Spring brake hold-off air is exhausted through the spring brake relay valve.

Rear

Axle Reservoir

PP-DC® PARK CONTROL 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 PP-DC valve should be inspected every six (6) months or 1500 operating hours, whichever comes ﬁ rst, for proper operation. Should the PP-DC 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 wear or physical damage. Repair/replace as nec essary.

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. Repair or replace as necessary.

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