Train and Main Line air?

[Deleted]

What's the difference between the two?

Taa muchly ,

Sam

[q8]

About 20Lb per sqaure inch. One (ML) is for the operation of doors and other air driven equipment. The other is (on older stocks) solely for the operation of the westinghouse air brake. On modern stocks there is no Westinghouse so only ML air is needed for all purposes.

[Colin]

Or in slightly more detail (if you don't mind Q8):

All trains have main line air, which is charged by the compressor's. It is used for the motors, doors, whistle, window wipers, coupler machinery, to apply the 'ep' brakes and, on trains that have it, (ie 'A' & 'C' stock) it supplies the train line.

As you can see, the train would be 'dead' without it, that's why it's known as the 'main line'.

The train line is supplied by the main line at a lower pressure and is used for the westinghouse (pure air brake), deadman, tripcock and other safety devices. Also if a train should separate, the train line is not 'protected' at the couplers, so any loss would force the westinghouse brake to apply (of course other things would happen, but that's the basics).

On more modern stock such as the 73ts or 'D' stock - the train train line is replaced by electrical circuits.


I'm sure SB will be along soon, arranging my stock refresher training early ;D ;D

[Deleted]

So presuming that you 'lost' Main Line air, would there be a valve or something to protect the train line air?

Taa,

Sam

[Christopher J]

Main Line Pipes have Star Valves on the ports of each car, so if for example two cars break away the the Valves will close on the end of the two disconnected Main Line Ports thus preventing Main Line Air escaping into the Atmosphere.

On Main Line air only Trains (73TS, D Stock ect) if there is a break away the 50v 'Round Train Circuit' will be broken causing an Emergency Brake Application.

Train Line Pipes don't have Star Valves, so if there is a break away on a Train Line Pipe, the air will escape into the Atmosphere causing the Triple Valves on each car to allow air from the Auxiliary Reservoirs to the Brake Cylinders to apply the brakes.

Main Line and Train Line are set to different pressures (if they were set at the same pressure, AFAIK they wouldn‘t work properly), Main Line Air is set to 85psi and Train Line is set to 70psi, when the Train Line is charged from the Main Line it goes though a 'Feed Valve' which changes the pressure down to 70psi, do you want me to explain how it works technically?

(Like this:)
Main Line Air (85psi) ---> FEED VALVE ---> Train Line Air (70psi)

[Colin]

ca55ie said:

So presuming that you 'lost' Main Line air, would there be a valve or something to protect the train line air?

Taa,

Sam

If main line air is lost, the train line will also be lost as it is supplied by the main line. Train line is not protected as it supplies saftey systems.

[Deleted]

christopherjolly said:

(Like this:)
Main Line Air (85psi) ---> FEED VALVE ---> Train Line Air (70psi)

Where did you copy that splurge from then ? ;D

With mainline air, the train can still operate up till about 4 bar, when the spring aplied parking brake comes on. This will only come off if the brakes are islolated or Main Line Air goes back above 4 bar.

[piccadillypilot]

christopherjolly said:

do you want me to explain how it works technically?

Yes please, I haven't got a clue. ;D

[Christopher J]

metapprentice said:

christopherjolly said:

(Like this:)
Main Line Air (85psi) ---> FEED VALVE ---> Train Line Air (70psi)

Where did you copy that splurge from then ? ;D

Copy? COPY!? All my own knowledge sir.

piccadillypilot said:

christopherjolly said:

do you want me to explain how it works technically?

Yes please, I haven't got a clue. ;D

Pistons, a High Pressure Spring, a Low Pressure spring and a Pilot Valve. I can explain it more deeper but it would mean making a diagram but I am not the most artistic sort. ;D

[Deleted]

piccadillypilot said:

christopherjolly said:

do you want me to explain how it works technically?

Yes please, I haven't got a clue. ;D

Yeah PP!!! ;D ;D

In the old 'Railway Training Centre' (halfway down Wood Lane between White City and Shepherds Bush) the 'train equipment' section had a room with pipes and reservoirs coloured red, blue, and green. These actually had compressed air in them - plus all the valves, operating handles, isolating cocks, and similar stuff that was fitted to trains in those days. Lots of chalk-dust (from the blackboard) was blown-up off the floor and into the air when the instructor set-up a defect (with air escaping from this pipework) for us to do the necessary isolations to 'get the train moving again'.

All of us 'oldies' will remember forever that main-line air is RED, train-line is BLUE, and equalising air is GREEN!!
That's the way we were taught how to deal with 'air' defects on trains in those bygone days.

On old ('A' and' C') stock, main line air is kept at 75-90 pounds per square inch, and train line air at 65 via a feed-valve.

Pete

[q8]

Brief explanation of a feed valve. A small piston with a 20lb spring behind it at the "rod" end. Mainline air at 85lb PSI pushes the piston back and charges the train line. When the air pressure behind the reaches 66lb PSI that combined with the 20lb spring pressure closes the valve. As train line air is used for braking or the pressure drops off it is maintained automatically but the valve. I have a diagram somewhere that I'll scan and post.

[Deleted]

christopherjolly said:

Copy? COPY!? All my own knowledge sir.

hhhhhmmmmmmm, seems just like you have copied it out of a text book! Oh well! ;D

[trainopd78]

colin said:

ca55ie said:

So presuming that you 'lost' Main Line air, would there be a valve or something to protect the train line air?

Taa,

Sam

If main line air is lost, the train line will also be lost as it is supplied by the main line. Train line is not protected as it supplies saftey systems.

EDIT: sorry to those of you who read earlier posting, but I was thinking of 59 stocks. Blonde moment!! On C stocks the feed valve does indeed work both ways, so if you lose main line air, you also lose train line air acordingly. This is why we need to put the combined traction brake controler into lap to find out which air we are actually losing.

[Deleted]

Lap being the position that holds all the air in the brake and air system still, which would presumably show which line of air you were loosing... I getcha...

Thanks for that everybody....

Sam