The spring brake assembly is bolted to a mounting bracket on the axle. The spring brake pushrod clevis is attached to a slack adjuster which is attached to a camshaft. As the spring brake pushrod is extended from the chamber, either by the parking/emergency brake or by service air pressure, the linear force of the pushrod is converted to rotational force by the slack adjuster and camshaft. This spreads the brake shoes against the brake drum.
When air is applied to the parking/emergency brake, the load of the heavy spring is released allowing the wheels to turn. When the driver steps on the brake pedal, a signal is sent to a relay valve that then sends air pressure to the service chamber of the spring brake. The air pressure causes the pushrod to extend which in turn applies the brake. This air pressure is released once the driver takes his or her foot off of the brake pedal.
The spring brake is designed to apply the the brakes automatically in the event that there is a loss of system air pressure. This happens because the air pressure holding back the heavy parking/emergency spring disipates allowing the spring to extend the pushrod which in turn applies the brake.
Brake chamber and spring brake actuators are used in Air braking system. mostly in heavy vehicles (Trucks).
Brake chambers are used in Front axles and spring brake actuators in Rear axles.
The main difference between Spring brake actuator and brake chamber is, Brake chamber doesn’t have hand-brake function but Spring brake actuator does have hand-brake function.
It has only one function, whenever air enters into the chamber, diaphragm gets expand and pushes the pushrod then the push rod pushes the slack adjuster then slack adjuster rotates the S-cam shaft and so on. when driver releases the brake pedal the return spring push back the diaphragm to its original position
Spring brake actuator:
See that GIF pic (donno GIF works on all devices), The red color one is second chamber , and blue one is normal brake first chamber. there is separation between those two chambers and there are different diaphragms for each chamber. (Refer the image)
First chamber/service brake chamber (Blue color) : when driver applies the brake , pressurised air enters into first chamber(See that blue colour), diaphragm expands and the diaphragm pushes the pushrod hence brakes applied. (Just like brake chamber working)
second chamber/Spring brake chamber (Red color): in this chamber pressurised air is available all the time, this pressurized air holding back the Large coil springs not to expand which connected to pushrod . so whenever driver applies the HandBrake the pressurized air which was holding the springs in second chamber gets released into atmosphere hence the large coil springs get expanded and pushes the Pushrod.