Technical Bulletin
Bulletin No: TCH-003-056
Subject:

Initial Release Date: 11-20-2019

Revision Date: 2-10-2023

Page: 1 of 1

BENDIX® PP-1® & PP-8™ PARK CONTROL VALVE WEAR AND REPLACEMENT NOTICE

This bulletin applies to all Bendix® PP-1® and PP-8™ valves in applications where the exhaust port is plumbed
external to the cab. It is mostly applicable to vehicles used in high-park-brake-cycle count applications, like refuse
vehicles or city buses.
When a heavily-worn PP-1 or PP-8 control valve is combined with restrictive exhaust plumbing, the vehicle park
brake force may be reduced. Valve wear may be the result of high-park-brake-cycle count and/or sideloading.
Sideloading can be caused by pushing or pulling the valve button at an angle and not in line with the valve or from
hanging objects from the button. See the table below for troubleshooting recommendations.
Bendix® PP-1®
Control Valve

Bendix® PP-8™
Control Valve

Valve
Bottom
View

PP-1
Located here for
PP-1 & PP-8 valves

Exhaust Port

Bendix® Valve
Model

Exhaust Port
Port Size
1/8” NPT

PP-1 & PP-8
®

™

1/4” NPT

Fitting

Tube

No

No

Yes

Yes or No

No

No

Yes

Yes or No

Recommendation
Maintain valve per Service Data sheet SD-03-3611.
Follow the procedure below.
Maintain valve per Service Data sheet SD-03-3611.
Follow the procedure below.

DIAGNOSING A LEAKING PP-1 AND PP-8 PARK CONTROL VALVE
When performing any inspection or service, follow the steps below and refer to the guidelines outlined in the PP-1
and PP-8 Service Data sheet SD-03-3611, or instruction sheet as applicable.
1. Run the vehicle until the air system reaches full reservoir pressure (120-135 psi). Turn off the vehicle.
2. Move the control valve button & plunger from side to side and up and down. Do not push the button in. If there
is any play, or if audible leakage is detected, the valve must be replaced.
3. Identify the dash valve exhaust hose location (generally near the grill). With the button pulled out (exhaust position),
there should be no audible leakage. Rotate the button and plunger in a clockwise direction – stopping every 90º
to check for leakage. A second inspector near the end of the exhaust hose would be helpful for this procedure.
There should be no audible leakage in the cab or from the exhaust hose at any point of rotation. Using a soap
solution, check for leaks. The allowable leakage should not exceed a 1” bubble in 5 seconds at any location on
the valve.
4. Push the button in (applied position) and check for leaks. The leakage should not exceed a 1” bubble in 3 seconds
at any location on the valve.
5. Reduce the supply pressure. At a pressure from 60 to 20 psi, depending on the spring installed, the button should
pop out automatically, exhausting the delivery volume. (This does not apply to the PP-8 or some PP-1 valves
without an automatic exhaust feature).
For additional assistance contact the Bendix Tech Team at 1-800-AIR-BRAKE, option 2
(1-800-247-2725, option 2) or techteam@bendix.com.
TCH-003-056 Rev 001 © 2023 Bendix Commercial Vehicle Systems LLC, a member of Knorr-Bremse • 2/23 • All Rights Reserved