Lecture Note No

PRINCIPLE OF OPERATION OF EK TYPE DISTRIBUTOR VALVE- By M.K.DE, LECTURER/IRIMEE

Introduction: Air brake is replacing vacuum brake system continuously since introduction on account of its merits over former system. Efficiency of highly appreciated air brake system largely depends on reliability of single equipment –DISTRIBUTOR VALVE (DV)

Standardised version of DV RDSO has standardised two types of DV for use in Indian Railways. They are: KNORR type C3W (WABCO) type Though there are few differences between these two types DV in respect of their construction and internal mechanism, by & large both are working on the same principles.

Function of DV The functions of DV are:  To control brake application as required by the driver.  To control release of brake as required by driver.  To isolate brake system when required.  To release brake manually when required.

Principle of working a) Charging:  Air pressure of 5 kg/cm2 is fed to each DV from loco compressor through main reservoir, C-2 relay valve, MU-2B valve and A-9 valve in the loco and through train pipe and dirt collector in the coach/wagon. The normal requirement of free air delivery is 3000ltr. /min.for a rake. Controlled air pressure flows into DV through Common pipe bracket placed at the back of the distributor valve. While the DV isolating cock is vertical, BP inlet passage of R-charger remains open. BP pressure flows directly to above of the main diaphragm. The pocket above the main diaphragm is termed as BP pressure zone of distributor valve. This pressure line is diverted to A-controller and after passing through the choke of A- controller, this pressure flows to below of the main diaphragm. The pocket below the main diaphragm is termed as CR pressure zone of distributor valve. This pocket is connected to control reservoir of 6-litre capacity positioned at the back of the common pipe bracket. BP line flows from R-charger (initial pocket) to and through Intermediate piece with cone of R-charger (middle pocket) to Auxiliary reservoir. Auxiliary reservoir pressure flows through two parallel paths viz. Maximum pressure limitter and Minimum pressure limitter.This pressure line is brought to top cover valve assembly and R-charger(third pocket). Main line pressure is restricted to flow to Brake cylinder line. BP, CR, AR pressure lines are restricted to flow to atmosphere. BC line is connected to atmosphere through DV.  In case of twin pipe working Auxiliary reservoir is fed by Feed pipe at a pressure of 6kg/cm2. b) Brake application  To initiate brake application BP pressure is lowered by operating A-9 valve. Pressure difference across the main diaphragm is realised. Higher CR (compared to BP) pressure inflates main diaphragm upward. Due to upward inflation, 3-pressure valve lifts the valve

plate from its seating and opens BC inlet passage. AR pressure then gets connected to BC line and brake cylinder pressure starts building up.  Pressure from AR to BC line flows through two independent paths. One path is through unrestricted path of minimum pressure limitter. This results in immediate rise of brake cylinder pressure. As pressure rises to 0.8kg/cm2, minimum pressure limitter closes this path. This helps in overcoming brake-rigging resistance. This is known as INSHOT BRAKE APPLICATION.  AR pressure now flows through maximum pressure limitter only. In this path flow is restricted by the provision of application choke. The size of the choke dictates the time to raise brake cylinder pressure. This path is closed when BC pressure reaches to 3.8 kg/cm2.  As BP pressure reduces, CR pressure has the tendency to flow back to BP line. The BC pressure working on A-controller valve checks the back flow of CR to BP line.  During BP reduction by the driver, each DV vents certain amount op brake pipe pressure through U-controller port. This helps in uniform brake propagation in the entire rake. This local reduction of BP line stops when BC pressure reaches to 0.8kg/cm2.  BC pressure working on equalising diaphragm tries to bring down 3-pressure valve. As soon as downward brake cylinder force equals to upward CR force in conjunction with BP pressure, hollow stem comes down maintaining both BC inlet & outlet passage closed. Brake cylinder pressure settles at this point. This is known as SELF-LAPPING. Thus graduated brake application takes place. c) Brake Release  When BP pressure is recharged to 5kg/cm2 pressure differences across the main diaphragm vanishes. The hollow stem comes down. This closes BC inlet passage and opens BC out let passage. BC pressure vents to atmosphere through release choke.  If BP pressure is enhanced but at lower pressure than CR pressure, BC pressure sets at some other lower value by self-lapping process. This is graduated release. d) Isolation  Rotating the isolating handle to horizontal position isolates DV. In this position AR pressure vents to atmosphere. There is sudden drop of BP pressure as AR drops .This is due the fact that BP tries to charge AR and simultaneously vents to atmosphere along with AR. This causes immediate brake application. For isolating DV following procedure is to be followed. 1. Close AR Isolating cock. 2. Isolate DV handle. 3. Pull Quick Release Valve and ensure that brake releases. d) Manual Release  The physical action for manual release involves single pulling of quick release lever attached with bottom cover of distributor valve. In normal condition, CR pressure is restricted to flow to atmosphere by providing K-ring on the pin assembly.  By pulling lever of the Quick Release Lever, Pressure rod (of QRV) lifts the pin assembly. CR pressure gets passage to flow to atmosphere through holes provided on control sleeve and then through passage of pressure rod. CR pressure starts venting to atmosphere till it equalises with BP pressure.  Since BP and CR pressures are equal, brake cylinder pressure starts releasing similar to normal RELEASE.