The working principle of the quick release valve. In the non-pressurized state, the skin membrane is in a free state. When the 1st source line has steam, the pressure pushes the membrane down. Compressed air is introduced to the number 1 source line, causing the skin membrane to curve down, compressed air to the brake chamber. When the pressure at port 1, suddenly decreases, causes the membrane to curve upwards. This leads to compressed air being released through the number 3 vent. Make the brake chamber depressurized as quickly as possible.