Lecture 6
PNEUMATIC CIRCUIT OF MOTOR AND TRAILOR COACH
The compressed air is required in EMU rake for following purpose: -
i) For keeping pantograph in raised portion.
ii) For working of RPC equipments
iii) For working of Hooter and wipers
iv) For application of EP and auto brakes.
The Compressor is fitted in under frame of Motor coach, it works on 1500 V DC. It is controlled by compressor governor and is started by 110 V DC supply.
In Motor Coach, the air from atmosphere is sucked through suction strainer where the dust is arrested and only clean air is allowed to go ahead. This air goes to low-pressure chamber where the air is compressed to the pressure of 3.0 Kg./cm2. This compressed air further goes to intercooler where the air is cooled. Then the air passes through an automatic drip valve (ADV) where the moisture of the air is blocked and only dry air is allowed to go further to HP (High pressure) chamber. Here the air is compressed to the pressure 5.6 Kg/cm2 to 7.0 Kg/cm2. This compressed air goes to after cooler, where the air is again cooled.
This cooled air goes to Main reservoir through a non-return valve (NRV) where the air is stored. These are two main reservoirs and between there is a cooling pipe. Now the compressed air from the main reservoir goes to MR pipe through a pipeline filter and main MR cock. A connection for compressor governor is taken before Pipe Line Filter. The compressor governor switches on and off the compressor when the pressure is below 5.8 Kg/cm2 and above 7.00 Kg/ cm2, respectively. In case of leakage of compressor governor, compressor governor cock isolates it, which is in series with it. In case of compressor governor setting does not stop the compressor working when the pressure is above 7.0 Kg/ cm2, then excess pressure is exhausted through the safety valve when the pressure is above 7.2 Kg/ cm2. In this way the MR pipe is charged and this pressure is supplied to C coach & A coach through MR hose pipe and coupling cock.
A connection of air is given to the RPC Reservoir from MR pipe, through a strainer or pipeline filter, reducing valve or limiting valve and non-return valve. Reducing valve reduces the MR pressure from 7.0 Kg/ cm2 to 5.0 Kg/ cm2. As RPC equipment and Pantograph requires 5.0 Kg/ cm2 air pressure.
The air is stored in RPC reservoir to supply to RPC equipment and pantograph even if MR pipe pressure drops. The air from RPC reservoir further goes to RPC equipment and pantograph through screw down cock.
An another connection of air is given to hooter reservoir from MR pipe, this air further goes to hooter through hooter cock, foot operated valve (FOV) and stainer.
A connection of air from MR pipe is given to combined brake unit through stainer and EP (Electro Pneumatic) cock, for EP brake
Application.
The air from MR pipe is also charges the brake pipe (BP) and the equalising reservoir. When the isolating cock switch (ICS) is open, the ICS reduced the MR pressure 7.0 Kg/cm2 to the pressure 4.7 Kg/cm2 before charging the BP and equalizing reservoir.
When the pilot valve in Master Controller is operated it activities the emergency application valve (EAV) and the air in Brake pipe is connected to exhaust through a deadman cock. A control governor is provided which ensure that the pressure in the BP (Brake Pipe) is exactly 4.7 Kg/ cm2. The brake pipe is also connected to C coach and A coach. brake pipe through BP hosepipe and coupling.
The air in BP also charge auxiliary reservoir through the auto cock and combined unit. The air of auxiliary reservoir is given to brake cylinder when the brake pipe pressure reduced towards zero. The air is given to brake cylinder from MR pipe and auxiliary reservoir. Through the additional limiting valves, which reduce the air pressure to 1.8 Kg/ cm2, safety valve and release and bogie cock. The safety valve leakes air, if the air pressure is 2.0 Kg/ cm2. In case of non-function of ALV. The case of brake binding the air in brake cylinder is released through releasing valve.
The pressure of air in MR pipe and brake pipe is shown duplex gauge, the pressure of air in brake cylinder is seen in brake cylinder gauge. The pressure of air in brake cylinder gauge is taped before the bogie cock.
IN ‘C’ COACH
The MR pressure is stored in the supplementary reservoir through pipeline filter & supplementary isolating cock (SIC). The air is further given to combined brake unit for EP brake application, through a strainer and EP cock.
A connection of air from MR pipe is given to hooter reservoir, then the air is goes to hooter through hooter cock, foot operated valve (FOV) and a strainer. Also from hooter reservoir a air connection to given to wiper through its cock.
The MR air is given to brake pipe and equalizing reservoir through pipe line filter, feed cut off magnet valve or its by pass cock and ICS, when ICS opened the ICS reduced the air pressure to 4.7 Kg/ cm2
The air in brake pipe is connected to exhaust though dead man’s cock and emergency application valve when the Master controller handle set life up in on position. The pilot valve is operated and brake exhausts through exhaust valve, which activate the emergency application valve and the brake pipe discharge heavily and auto brake are applied. The air in brake pipe is also connected to exhaust through dead man’s cock, emergency application valve (in normal position) exhaust magnet valve and it by pass cock, AWS applied auto brakes.
The air path to combined unit is just similar to B coach or Motor coach except a tapping is taken of air before bogie cock, which given air to the self lapping cylinder in the ICS, which helps in gradually application and lapping of EP brake. The same pressure is seen in brake cylinder gauge.
The air in brake pipe is also connected to exhaust when guard emergency brake cock is turned ‘ON’ and the auto brake are applied. The pressure is brake pipe is also seen in GUARDS gauge.
IN ‘A’ COACH
The MR air is stored in supplementary reservoir through pipeline filter/strainer given to combine isolating cock. The air is further given to combined brake unit for EP brake application, through a strainer and EP cock.
The air in BP is connected to combined unit through auto cock, the air path after it is just similar to that of B coach, except here there is no tapping for brake cylinder gauge and self lapping cylinder.
In B coach there are 8 brake cylinders and in C coach and A coach. There are four brake cylinders.
The MR reservoir, supplementary reservoir, hooter reservoir, RPC reservoir and pipe line filters connected in MR pipe has a drain value for draining the moisture and dust in the air.
The auxiliary reservoir, equalizing reservoir and pipeline filter connected to BP do not have drain valve.
AUXILIARY COMPRESSOR (BABY COMPRESSOR)
When the MR pressure is zero then the raising of the pantograph a small compressor known as Auxiliary compressor or baby compressor will be used the initial pressure. The auxiliary compressor works on 110V supply from battery. But when the baby compressor is not working than a bamboo stick is used to raise the pantograph. It is not advise to use bamboo stick during rainy season.
PANTOGRAPH
Pantograph is an equipment provided on the roof of the Motor coach, for current collection. It is held in its raised position by air pressure, in addition it has a spring tension. If pantograph is removed from the panto frame than the frame will remain in raised position, which means weight of the pan is also essential for lowering the pantograph. The pantograph used for EMU services is fitted with a single pan and designed to be raised by compressed air and lowered by a spring. There are three adjustable springs fitted on pantograph out of which two springs balance weight of moving parts and in addition provided the contact pressure. The inner [push down] spring operate lever roller and came to over come, the forces of the outer spring and hold the pantograph, positively in the down position. This effect of the inner spring is cancelled by the operation of the piston. When the air is admitted to the cylinder, the pantograph raise, comes into contact with OHE wire and exerts the required control pressure. Panto Control valve at the end of the cylinder contacts the raising and lowering of the pantograph in such a manner that: -
(a) When raising the speed is low, so that pantograph makes contact gently with the OHE, to avoid damage to pantograph and OHE wire.
(b) When lowering the contact with OHE wire is released quickly and the pantograph comes down slowly and rests on panto platform, very gently so as to avoid any damage to panto platform or panto frame. The minimum pressure required to raise pantograph is 3.5 Kg/ cm2
out 5.0 Kg/ cm2
pressure is set to panto cylinder to make a firm contact with OHE.