Description

Overview

Williams Controls designed the ratio relay valve to deliver proportional air pressure control for heavy-vehicle brake systems. Furthermore, the valve provides reliable modulation under varying loads, so multi-axle trailers keep a stable brake response and predictable feel. Additionally, its compact body and serviceable layout make a practical replacement when you refresh ageing trailer brake hardware.

Features

• Three-way, compensating, pilot-pressure-operated relay design.
• Output pressure proportional to control pressure for consistent braking.
• Adjustable output/control ratio on WM318 series variants for quick tuning.
• Suits heavy-vehicle trailer applications and FMVSS-type systems.

Specifications and Materials

Part number: A88053.
The WM318 family typically uses 1/4 NPT ports and an unthreaded exhaust, and the body uses durable materials with internal components built for reliability in pneumatic brake circuits. For engineering detail on the WM318 family, see the manufacturer technical catalogue manufacturer technical catalogue.

Compatibility and Fitment

Use this valve on ratio-controlled trailer brake systems where proportional output improves trailer balance. 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.
WM318-A, 112201

Compliance and Safety

Follow heavy-vehicle brake service procedures when you install this valve. First, depressurise the system before you disconnect lines. Then fit the valve using correct fittings and OEM torque values, and perform leak checks. Finally, conduct dynamic brake tests in a safe area before you return the trailer to service. Also, only qualified personnel should service air brake equipment.

Trailer Applications

For example, use this valve on tandem and tri-axle road freight trailers where ratio-controlled relay action improves braking balance. Moreover, it helps maintain consistent trailer response across typical Australian freight operating conditions.

Cross-reference and Suitability

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

Why Choose ICS Trailers

We focus on heavy-vehicle trailer parts with verified specs and clear guidance so you can service brakes with confidence. In addition, our team curates related pneumatic fittings and protection valves that work together reliably to keep your vehicles road ready. Browse Air Brake Parts at ICS Trailers