Your cart is empty
Browse our catalog to find the parts you need.
These images are illustrative and may not match the product exactly. Always verify by part number — or confirm instantly with the assistant using a photo or VIN.
PAI · Air System
802552
In stock · ships from Knoxville
The 802552 is a charging-style relay emergency valve used on heavy-duty truck and trailer air brake systems.
Confirm the part fits before you buy. Applications and interchange numbers are researched and audited per part.
Verified fitment for 3 applications
Add your truck to see whether it's one of them
All confirmed applications for this part number.
Mack Trucks
Volvo Trucks
Other applications
Mack Trucks
Volvo Trucks
Other applications
Designed as an aftermarket replacement for Mack and Volvo original parts, but also fits various older trucks and trailers with 4.5 PSI crack pressure, charging-style systems. Do not use on converter dollies, turntable axles, or lift axles. Verify compatibility with your specific air system before installation.
Part data verified against 2 catalog sources
Numbers this part supersedes or interchanges with. Showing 13 of 13.
Different year, make, or config? Get a confirmation against your truck in under a minute.
It acts as a fast-acting relay between the air reservoir and the service brake chambers, ensuring quicker brake application and release. The valve includes a 4.5 PSI crack pressure and a ratio feature that provides a 1:1.5 boost during panic stops for less than 0.01 seconds. It is commonly used to replace the original equipment on pre-FMVSS-121 Mack and Volvo trucks, as well as many other older trailers. Replace this valve if you experience slow brake response, air leaks, or improper pressure balance in the system.
Part Number: 802552
RELAY VALVE
Vendor: PAI Industries
Dealer: Knox Trailers
Compatibility, alternatives, and more
Parts commonly needed alongside air system
