What is the purpose of the 'Spring Brake Chamber' (e.g. Type 30/30) in heavy vehicle air brake systems?

1. To act as a mechanical parking and emergency brake using a powerful spring when air pressure is lost
2. To absorb suspension shocks from the road surface using internal air springs
3. To increase the speed of air release when the foot pedal is released
4. To store reserve compressed air for up to three emergency stops