Fitting air brakes on locomotives

HI you must have a grease and oil separator on the air brake system on the loco to keep the system fairly clean. FISH7373 81C

 

I seem to recall 5029's ended up on the firemans side running plate basically as there is supposedly no place big enough to hide it on a Castle ?, like you I can recall plenty of incidents where a tempremental air pump was the root issue.

 

That'd be the preferable option to the loco being a failure and the train being cancelled.

 

The Westinghouse brake was introduced on the LBSCR in 1878 (and maybe slightly earlier elsewhere, I don't know) so the pump technology is effectively the best part of 140 years old. It would be interesting to know the failure rates in today's usage as against that suffered by those railways (LBSCR, GER etc) that had it working in day-in, day-out service (and presumably had maintenance procedures honed to a T).

Tom

 

As you say, 'Westinghouse' pumps have been around for a long time and must have a good track record A lot of the problems may well be down to unfamiliarity with the technology. The last pockets of air brake operation with steam locos were few and far between and anyone with good experience is likely to be well into their seventies. I've a lot of steam experience but virtually none with steam driven reciprocating air pumps. Things aren't helped by the majority of pumps being hidden away, which always provides a maintenance headache.

How do the 'modern' pumps compare with the older ones? Are they vastly different or pretty much the same?

 

As I said, I'm not certain but it is in the back of my mind that others have not been allowed to copy Clan Line's example and I can't think that I've dreamed it. You never know, though!

 

I wouldn't have thought that a turbine driven screw compressor would be as efficient as a reciprocating pump, therefore the steam consumption would be higher. Turbines need a high pressure superheated steam supply to run really efficiently and loco boilers do not run at high pressure, let alone at a decent, constant superheat temperature..

 

I think you might just be swapping one bit of mechanical equipment for another, with no real guarantee that it would be more reliable. Historically, Westinghouse pumps must have had a very high reliability, operating with minimal attention from the crew over a wide range of pressures and brake demands. So if it is worse now (and I don't know definitively it is), then I suspect it is due to a collective loss of the kind of unwritten experience that fitters of old dealing with the pumps day-in, day-out would have had.

Tom

 

Now, if only the GWR had used smoke deflectors..............!

 

Icant understand why air pumps were not fitted to the tender side just by the side of the shoveling plate , it could exhaust into the waterspace, and be shielded by a removable plate, so its not noticeable from the outside, and can still be serviced and fixed from with in the cab

 

Have you ever stood next to an air pump when working? They are not the quietest bits of kit. With all the noise in the cab. The air pump would drown it all out and nothing will be audible.

 

Terriers seem to manage with the pump hung on the outside of the cab.

 

The GWR normally mounted its Westinghouse air pumps on the side of the smokebox.

 

Not sure it would work so well. The only case I can think of using turbine driven compressors is an IC engine turbocharger (not including gas turbines), where centrifugal compressors are used which match the turbine speed and torque characteristics very nicely, but rarely with more than 2 bar boost (29 psi gauge). Getting 10x pressure ratio out of one of those over a wide range of demand rates could be interesting. Of course, you could stick a (very) high-speed reduction gearbox on the shaft and drive a screw compressor, but that's some serious added complexity. Feed water turbo-pumps are a different matter, the much higher density (approx 800 times greater) means that you don't need anything like so much rotor speed to get a significant amount of dynamic pressure. Turbo generators can match the alternator winding to the speed of the turbine and the voltage requirements.

Regarding the work to accelerate the piston and rod, one of the neat characteristics of the basic Westinghouse pump is that once under load the thing that absorbs all that kinetic energy should be the air in the cylinder when the steam cuts out. Admittedly, the simple pumps are all running steam at near enough 100% cutoff, so not that efficient. Bigger US locos have cross-compound pumps (often two), where the HP steam cylinder drives the LP air and vice-versa; I expect they're significantly more efficient. Despite that, one book I read recently (which I can't be bothered to find at this time of night) suggested that the steam demand for a Westinghouse system was about a third of that for vacuum brakes, so even if the pumps weren't efficient the system efficiency was better than the alternative. Norman McKillop certainly wrote about the pumps being an occasional source of frustration on the NBR, and Bill Harvey writes of managing to change the top head in 35 minutes (suggesting that this was not an infrequent requirement) but then no mechanical device will be as reliable as something simple like an ejector.

 

I remember reading, many moons ago, in one of those "reminiscences of my life on the footplate" type books a comment that having the pump on the outside of the cab made it easier to hit with a hammer when it got stuck...

The benefits of simple but robust technology!

Steve B

 

There are a number of different types of rotary air compressor apart from screws and turbines, which offer near 'positive displacement' compression. The benefit is the lack of valves which can stick and other bits which need lubrication. The tricky bit is driving them in an efficient fashion. The electrical power drawn is significant, and I can't see that using a turbo-alternator set to provide that power is really sensible - you might as well just connect the steam turbine directly to the air compressor. The problem then is controlling the set at low demand - turbines like to run at constant speed, and efficiency at low speed would be dire.

The Advanced Steam Traction Trust (ex 5AT group) intend to look at this IF there is a demand for it, and we discuss it from time to time, but it's very much on the back burner due to more pressing projects for real customers right now.

At least we have a debate going at last - I thought previously I was trying to flog a dead horse.

 

According to Cook when there was a committee on unification of brakes in the early 1920s who did some extensive trials, and in order of steam consumption it worked out 21" large small ejector was greatest, then GW air pump/ejector/21" narrowly more than Westinghouse, and GW air pump/large ejector/25" was best. They made a special rig to work out steam consumption of the air pump. He mentions the other issues was that the Westinghouse setup was rather more expensive. In the end he says that although they agreed on vacuum as being the best option, ere was an element of agree to disagree about it, because the GER insisted they couldn't work their intensive suburban services without the quick release of the Westinghouse and the GW retained 25" vacuum as their stock was designed for it.

Although not a valid comparison I think its interesting that every shop I remember when I was in the motor trade had a reciprocating pump, albeit electrically driven of course for the air tools. I don't know if that's changed now. There was always the issue of having the noise out of the shop but somewhere where it couldn't get too easily 'borrowed'...