An air brake chamber is a component of an air brake system that converts compressed air pressure to mechanical force. The brake chamber contains a rubber diaphragm, which expands when air pressure is applied to it, and extends a push rod that ultimately applies the vehicle's brakes.
The air enters the chamber through a valve located on the front of the brake pedal and is delivered to the service brakes. The valve opens and delivers higher air pressure as you press the brake pedal harder.

Brake Chambers are made in different styles, types and sizes. Each has a corresponding pushrod stroke-adjustment limit.
Almost all commercial vehicles use a type of brake chamber that is held together by a clamp assembly. The Ontario Highway Traffic Act and regulations have set adjustment limits for these type of chambers.
Service Chambers
When the relay valve on a trailer allows air to enter a service chamber, air increases in pressure, displaces the rubber diaphragm and extends the steel push rod which ultimately applies the vehicle's brakes.
Spring Brake Chambers
A spring brake chamber is similar to a service chamber but has an additional chamber attached that gives it the ability to apply a parking brake when air is purposefully removed from the rear section of the chamber or an emergency brake when the air brake system fails and traditional braking is not possible.
The most common spring brake chamber is a 30/30 type with 24/30 and 30/36 being other examples. There are also long stroke variants that can add an extra margin for safety ensuring full brake application on systems that may be slightly out of adjustment or they are used to eliminate brake drag on some systems.