As a earlier Loco Pilot of Indian Railway I try to answer this. Train brakes operates through air pressure. air pressure create in Loco through two or three compressors. the created pressure store in four main reservoirs.
They are MR 1,2,3 and 4. These MR( main reservoir) situated two either sides of locomotive in under frame. MR maintain at 10 Kg/Cm. Here is pic of one main reservoir.
Each wagon is provided with a brake pipe and a feed pipe ( only in twin pipe brake system in passengers train).Brake pipe is green and feed pipe is white in co lour. here is pic where angle cocks are white and green in colour .
At the both ends of BP and FP one BP & FP isolating angle cock and BP & FP air hose pipe is fitted . The air hose pipe have a palm coupling .
The BP & FP of all wagons or coaches are coupled to making a single BP and FP running from locomotive to brake van. The all angles cocks are kept in open positions.
The angle cocks in front side of loco and back side of brake van are kept in closed positions. The BP pressure is Kg/cm and FP is 6 Kg/cm.
Working system:- every wagon has a DV ( distributor Valve) which has three connections. One is with BP, second one is with A.R. ( auxiliary reservoir) and third one is with B.C. ( brake cylinder).
The DV is balanced with 5 Kg BP air pressure. When BP pressure reduced by A 9 handle from loco by Loco pilot DV has been unbalanced and send the air pressure proportionately from A.R. to B.C. thus brakes applies.
When Loco pilot put A 9 handle in release position BP regain to 5 K.g and DV again get back to balance position. This time the air pressure of BC exhaust through DV and brakes release.
In twin pipe FP charged the another reservoir named CR ( control reservoir) in 6 Kg. In twin pipe CR’s kg pressure make DV balance quickly and brakes release faster than single pipe operation. thus in passenger train brakes release quickly than freight train. freight train operate in mainly single pipe and passenger train operate in twin pipe system. Here is pic of under frame of a wagon for your ready reference.
from left first one is BC , second is DV third is AR.
Images source Google.
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