Description

Overview

This air brake pilot relay valve helps reinforce the service brake signal on long wheel base trailers and converter dollies. It takes a relatively small control pressure and uses it to move air quickly from the supply line into the spring and service brake chambers. As a result, the valve helps distant trailer and dolly brakes respond with the same strength as the closer axles during both light and moderate applications.

Features

• Pressure equalising pilot relay design that maintains a 0 psi differential between control and delivery during normal operation, which supports balanced braking across the combination.
• Large 3/4″ NPT supply port with three delivery outlets sized for typical heavy trailer brake chambers so installers can route lines efficiently.
• Dedicated 1/4″ control port that lets the air brake pilot relay valve follow service brake pressure closely, even during light pedal applications.
• Compact relay body that suits chassis or dolly mounting near the rear axles, which helps shorten air line runs and reduce application lag.

Specifications and Materials

This R-8P style air brake pilot relay valve uses one 3/4″ NPT supply port, three delivery ports nominally sized 1/2″, and a 1/4″ control port. The internal design provides a 0 psi differential between control and delivery so all brakes in the combination see a similar pressure signal during service applications. This layout suits long wheel base towing trailers and converter dollies that need faster response and improved brake balance.

Crack pressure is effectively 0 psi, so the valve starts to relay air as soon as control pressure rises from the service valve. This behaviour helps even the most distant trailer axle contribute its share of braking effort, which can improve lining life balance across the vehicle set.

Part number: AB8474P.

Manufacturer style technical guide for the Bendix R-8P pilot relay valve.

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. 287114X, 107455, KN28300, R8P.

Compliance and Safety

Always park the vehicle on level ground, chock the wheels and fully drain the air system before you remove any relay valve. Then mark each hose and port so you can refit lines to the correct locations during installation. After you fit the new valve, recharge the system, carry out a full leak test with a suitable leak detection solution, and verify that all trailer and dolly brakes apply and release evenly from the driver’s seat.

Trailer Applications

Workshops commonly mount this air brake pilot relay valve on the chassis or converter dolly frame close to the rear axles. In this position, the valve can fill and exhaust the spring or service brake chambers quickly, which reduces lag compared with a foot valve only circuit. It suits long wheel base semi-trailers, B-double sets and converter dollies that must maintain stable brake balance across multiple trailers. However, always confirm valve choice and location against the original brake design or with a qualified brake specialist before you change any circuit layout.

Cross-reference and Suitability

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

Use this cross-reference list as an identification guide, then match ports, crack pressure and mounting against the vehicle’s existing valve before final selection.

Why Choose ICS Trailers

ICS Trailers focuses on heavy trailer braking and suspension parts, so you get components selected for real fleet conditions rather than light automotive use. Our team checks port sizes, crack pressure and cross references carefully, consequently you can match an air brake pilot relay valve with confidence. In addition, we back every listing with clear technical information so workshops can keep downtime low and maintain safe, predictable braking across the fleet.

Browse Air Brake Parts at ICS Trailers.