Air Pump Failures

Following yet another air pump failure this week (Nunney Castle), can anyone tell me the air capacity of a typical Westinghouse pump? e.g in CFM of free air and output pressure? I want to give this problem some thought. :-k

 

Hi,
You could probably find that out, but I would highly doubt that Nunney Castle has a good old fashioned Westinghouse pump. Most (if not all) have a much more modern variety of compound air pump from a withdrawn eastern European loco or specially built for the purpose.

Donkey pump:


Nunney Castle pump:




I think the air cylinder is at the top, with the two steam cylinders sit below the running plate, anyway the two are noticably different.

The old Westinghouse pumps have an odd reputation for unreliability which I personally think is a recent development, the LBSCR, LTSR and the Caley managed fine with them. The thing is to ensure it has plenty of oil as the reservoir on the top only holds so much. For info, a Westinghouse pump charges the Main Reservoir at 90psi for a Train Pipe pressure of 70psi. Main line railways use a twin pipe system with (I believe) the same pressures. It is all explained well on the Railway Technical pages here: http://www.railway-technical.com/air-brakes.shtml

 

The pump in the pics of Nunney Castle have the Steam cylinder above the running board and the Air side below, just like the first pic. The Air side of larger compressors are often finned to keep the cylinder cool (main res piping is run as long as possible for the same reason). The steam side is always lagged to retain heat.

The Compressor will charge the main reservoir to what ever the Governor is set to, but only up to boiler pressure. The train pipe pressure is set by a feed valve on the drivers brake valve.

 

Many of the answers are here, but in German: http://www.martynbane.co.uk/airpumps/airpumps.html

And also starting here:

http://www.bremsenbude.de/seiten/luftpumpe05.htm

 

I dont know if this will help with a translation.


http://www.freetranslation.com/

 

Thanks fellahs, that should give my grey cells something to chew on, but more info welcome both in regard of the compressor duty and the failure modes.

I've got a couple of ideas I want to investigate. Seems ridiculous that we've got trains sitting down on the big train-set and jeopardising the future of mainline steam due to a lack of compressed air.

 

How many air brake failures have actually been pump failures? Few I think. I don't have any stats but have a strong feeling that systems (esp pipework) have been at fault more often than pumps. That the pumps work reliably abroad on thousands of engines suggests they are not the weak link in the chain.

 

There is a simple solution to air brake failures. Don't have air brakes. A number of mainline locos operate quite happily with the good old fashioned vacuum brakes they were designed with. I believe a large number of the failures are down to the brake equipment being second hand equipment designed for use on diesel locomotives. There is a bit of a difference in environment between the two types that cant really help.

 

I dont beleve these are the issues. A number of locomotives with second hand air brake systems work with little problem. Clan Line has been functioning well with its "nicked off a 47" gear on the back of the tender. 45407 and 76079 do not have problems either. Of those 3 I don't remember a failure atributed to the brake system...

I do wonder if 5029's issue the other day may be more to do with the infrequent use. To start the equipment on a cold day 6 weeks after her last tour... A possible cause.

 

I've not trawled back through all the posts associated with tours which have been terminated due to air brake faliues as yet, but 71000 and No9 spring to mind too?

 

8RPH - Could you give some examples of AB system failures where the cause is one of the valves previously used on diesels?

 

I've translated this reference - very useful. Looks like the pump capacity is typically 1200 - 1500 lts/min (quoted as "free air" I assume) and a delivery pressure of 8 bar (absolute I assume) = 105 psig.

I'm considering both alternative compressor types eg turbine driven, or maybe a back-up compressor in the support coach.

 

Hm??????, the Polish pumps imported and fitted to the majority of dual braked mainline steam locomotives in Britain are quiet happy to supply air at 150 psi?

 

I cannot quote specific examples, but if as you said in your other post few failures are down to the actual air pump then in my view the control valves on the system would be the other likely cause. They are troublesome enough on the diesels they were designed for at times when not used frequently, Westinghouse feed cut off valves spring to mind for a start as being good things to stick. Throw into that the harsher environments on board steam locos and this can definately cause issues. With regards pipework. If its done properly with the correct wall thickness tube and fittings rated at the correct pressures and the runs are routed and supported correctly I honestly cant see how this could cause you many problems.

 

Thanks Ian. Do you need 150 psi though, or is the pressure reduced down to say 90psi in the brake system?

 

10 years ago, thats not bad!

Yes, sadly a steam pipe between engine and tender is no longer an accepted method. Also, it can reduce the water space.

 

1. Agree, but I was trying to highlight the fact that the failure was due to piping, not the pump and luckily the train was dual braked.

2. In its latest reincarnation where have they fitted Clan Line's air pump?

 

1. Dual braked stock would not help if an EWS crew are used as they are no longer qualified to drive trains on vacuum.

2. Clan Line still retains its tender based pump I believe - but this is not an option for any new AB systems.

 

Can someone please explain why this isn't allowed anymore? If you can run air, vacuum and water hoses between the engine and tender, running an extra steam hose wouldn't be a problem. It not as if the engine and tender are going to be separated, thus risking brake problems. Seems a little daft to me. Can anyone give a better reason that "its not allowed"?
Thanks,
Daniel