What is the purpose of the second main res air pipe on a UK Loco's buffer beam?

[tgm999]

There's the red for the train pipe and two yellows for the main res (usally only the one next to the red is used) what is the second yellow pipe used for?

 

[Class41]

Much of the rolling stock have only one Main Res (yellow) feed pipe, adjacent to the coupler, historically locos often have many more pipes, control air, (white), Vacuum, steam heat, Brake Pipe, etc. , the MR pipe is further away from the coupler, so to ensure they can connect, there is one either side, both teed off from the same MR pipe. More modern stock also have the electrical jumpers running through as well - an EMU can have 8 electrical jumpers between each car, then the only way of connecting the MR is to double up on the hoses, one each side, then they will always be adjacent to one another.

Some wagons, mainly from the continent, have no MR pipe at all, and just depend on the BP for air reservoir, these are known as Single Pipe vehicles.

 

[hairyhandedfool]

The fear of turning a piece of stock and not being able to connect the Main Air Res. pipe might be one reason, but note it is only really the older locos (like the 47s and 50s) that have two, newer locos (like the 60s or 67s) have one.

 

[Wyvern]

I believe this has always been a problem on London Underground. The control cables etc have to be on one side because of the gangways.

Thus note had to be taken of trains going round a loop being unable to couple up. Read it on District Dave's I think.

 

[MrC]

Some wagons, mainly from the continent, have no MR pipe at all, and just depend on the BP for air reservoir, these are known as Single Pipe vehicles.

Not sure about the continental bit as many older EMUs (such as the SR slamdoor & cl.442 EMUs) had a single pipe auto brake although they obviously they had a through MR pipe for the EP brake etc.

 

[ChrisCooper]

I believe this has always been a problem on London Underground. The control cables etc have to be on one side because of the gangways.

Thus note had to be taken of trains going round a loop being unable to couple up. Read it on District Dave's I think.

Most London Underground stock is only able to couple one way, they have an "A" end and a "D" end and can only couple A-D. As said, it's because the air and electrical couplings are no symetrical. On the Victoria, Jubilee, Bakerloo and District it doesn't matter as there are no situations where trains would become turned, the lines all being straight out and back. Circle, Central, Picadilly and Northern lines all have loops so trains will get turned in service. Central and Circle line trains can couple either way, having symetrical couplings. I think the double ended Picadilly trains do too, the single ended ones oviously can only couple one way. The Northern line stock is all single ended so cannot couple other than one way. I'm not sure about the old stock on the Northern and Central (1959, 1962 and 1972 stock). Trains on the Met can be reversed using the triangle on the Watford branch. I don't think it's used much at all though, and when it is care is taken to make sure the workings are equalised so trains are still the right way around.

 

[tgm999]

an EMU can have 8 electrical jumpers between each car, then the only way of connecting the MR is to double up on the hoses, one each side, then they will always be adjacent to one another.

That seems like a reson, thanks.

I thought that maybe it was for when the locos are double headed and used both main res pipes to fill the main res on both the locos quicker by using all the compressers.

 

[Class41]

That seems like a reson, thanks.

I thought that maybe it was for when the locos are double headed and used both main res pipes to fill the main res on both the locos quicker by using all the compressers.

The air supply on the MR pipe is set at 7 bar, and apart from supplying air to the brake cylinders, may be used for air suspension, sliding doors, toilet flushing, hopper doors and so on, according to the stock in use.

The compressor on the loco supplies air to the MR Pipe, and while it probably may lead to a faster supply when double headed, the one loco's supply should be sufficient. Indeed, unless one of the locos had failed and the compressor was not running, the MR pipes probably wouldn't be connected between the two locos, just rely on the inside loco's air to supply the train.