Description

Overview

Air brake pilot relay valve R-12P is a special purpose relay for trailers and converter dollies. It reinforces the service control signal so distant trailer axles see pressure that closely matches the lead trailer brakes. As a result, double and triple trailer combinations gain more even braking and better stability during light applications. Workshops use this valve when they need a 0 psi crack pressure relay that keeps control and delivery pressures closely aligned along the whole combination.

Features

• 0 psi crack and differential design that passes on small control inputs quickly so light pedal applications still reach the rear trailers effectively.
• Two 1/2″ NPT supply ports and four 3/8″ NPT delivery ports, which give installers flexible plumbing options on multi axle trailers.
• Pilot operated relay layout that boosts the control signal rather than acting as a simple on off valve, therefore helping keep braking smooth and progressive.
• Compact air brake pilot relay valve body that suits chassis or dolly mounting near the axles, which can reduce line length and speed up response.

Specifications and Materials

This R-12P pilot operated valve uses two 1/2″ NPT supply ports, four 3/8″ NPT delivery ports and a 1/4″ NPT control port with a dedicated exhaust outlet. The 0 PSI crack pressure means the valve starts relaying air as soon as control pressure rises off zero, which helps trailer chambers see the same application signal as the dolly brakes.

During service braking, supply air flows through the valve to the delivery ports until delivery pressure matches the control pressure, then the relay section balances and holds the signal. During release, the valve opens the exhaust path so air can leave the brake chambers quickly and restore free rolling.

Part number: AB8475.

Manufacturer technical guide for the Bendix R-12P trailer relay valves

Compatibility and Fitment

This cross-reference listing means this valve is a suitable replacement for the part numbers and applications shown. Some changes in air line plumbing may be required. 109264, 065476, 109001, 109002, 109424, 109446, 65476.

Compliance and Safety

Before any work on an air brake pilot relay valve, park on level ground, chock the wheels and drain the air system. Next, mark every hose and port so you can reconnect lines to the correct locations on the new valve. After installation, recharge the system and check every joint with an approved leak detection solution. If any wheel shows slow apply or release, stop the job and ask a heavy vehicle brake specialist to review the circuit.

Trailer Applications

Workshops fit this R-12P air brake pilot relay valve to long wheel base trailers and converter dollies in multi trailer sets. It usually mounts near the trailer service relay valve or reservoir so it can boost the control signal locally. In addition, the valve can act as a slave to an ABS controller on remote axles that need a matching pressure response. Always follow the original trailer brake layout or an approved modification drawing when choosing the mounting point.

Cross-reference and Suitability

This part cross-references to or suits the following equivalent part numbers and compatible alternatives:

Use this table as a guide when identifying existing trailer valves and checking that the R-12P pattern suits your application.

Why Choose ICS Trailers

ICS Trailers focuses on air brake parts for heavy trailers, so we match pilot relay valves to real fleet conditions rather than light trucks. Our team checks port sizes, crack pressure and common cross references carefully, therefore you can select a replacement with confidence. In addition, we back each listing with practical information so workshops can keep downtime low and maintain stable braking across multi trailer combinations.

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