When the pressure in BP is increased, the balance in the diaphragm assembly in the main valve is upset due to pressure raise in chamber 2, causing the position assembly to move downward and thus opening the exhaust valve. Ari from BC is released through passage of hollow stem and finally is let off to atmosphere through the “release choke goods” in freight condition and through both release choke – goods & release choke – passenger in passenger service condition.
Pressure in chamber 11of cut off valve under the seal caused the guide to lift up making the pin free the guide will not come down till the BC pressure reaches as low a value as 0.2bar and till such time valve 6 would be kept closed isolating CR and eliminating over charge in to CR Hedding. When the operating lever is pulled briefly, the locking rod slides down and gets wedged in between double release valve and its seat and facilitates draining of air from chamber 1 and also all the connected chambers. This upsets the balance of the diaphragm assembly and open the exhaust valve air from BC will be released and also the pressure in chamber 8 is reduced till a new balance is achieved thus facilitating a partial brake release. If the operating lever is pulled fully for a long time, the double release valve in the lower cover will be moved off their seats permitting complete draining of the entire system.