Passenger Emergency Alarm System:
The passenger emergency alarm system is provided between the main brake pipe and the alarm chain. When the alarm chain is pulled, the air pressure from the Brake pipe is vented out through the 8 mm choke provided in the Passenger emergency alarm valve. Due to the sudden drop in air pressure from the brake pipe in the system, the airflow indicator in the Locomotive deflects from its normal position and also gives hooting signal. By this, the driver comes to know about the drop in BP in the formation and he applies the brakes to stop the train.
The passenger emergency alarm system consists of two main parts:
- Passenger emergency alarm valve (PEAV)
- Passenger emergency alarm signal device (PEASD)
The passenger emergency alarm valve (PEAV) consists of a spring-loaded hollow piston fitted with a check valve at the bottom. It has also got a control chamber at the bottom of the piston and a brake pipe chamber at the top of the piston. An 8 mm diameter exhaust port is provided at the bottom of the valve to release the air from main brake pipe. The brake pipe chamber available at the top of the piston is connected with the PEASD through branch pipes.
The PEASD consists of a pilot valve which can be operated by pulling the chain by the passenger. It is also provided with two numbers of exhaust ports to facilitate the removal of air from the top of the piston (Brake pipe chamber) by pulling the chain.
During charging the brake pipe chamber and the control chamber of PEAV are charged with 5 Kg/Cm2, the control chamber is charged through the restricted passage. The air which is available at the brake pipe chamber at the top of the piston is also made available at the top of the pilot valve of PEASD.
During charging the spring loaded check valve closes the passage between main brake pipe and the exhaust of PEAV.When the chain is pulled by the passenger, the pilot valve in PEASD is lifted first.
The air from brake pipe chamber of PEAV is then released through the exhaust ports of PEASD and in turn, brings the pressure at the top of the piston to zero immediately. Due to the existence of control pressure at the bottom of the piston, the hollow piston gets lifted, which in turn connects the main brake pipe with the exhaust to deplete the air from main brake pipe to initiate brake application.
Resetting of PEASD:
Unlike vacuum brake, wherein turn the disc will automatically reset the valve, an air brake system in addition to the turning the disc, the key which is an integral part of PEASD has to be turned by 90 degrees clockwise.
In the recent modification, a wire rope is connected to the PEASD so that it can be reset from ground level eliminating the need to climb the coach for resetting the PEASD.