Spring brakes start to drag as pressure drops to 60 psi, and they release as pressure rises to 60 psi. Yet a full service brake application can be 100 psi. The coil spring in most spring parking brake chambers can exert a force of between 1,500 and 2,000 pounds. With a service brake application of 100 psi, a typical Type 30 brake chamber can produce a force of 30 × 100 = 3,000 pounds.