Advice...vacuum or airbrakes?

which is easiest to source/build if you are starting from scratch

 

i would imagine Air brakes, as much of it is availible off the shelf from manufactorers that make the gear for modern railway stock, , you can get vacuum cylinders, but in most cases not off the shelf. and certainly not at a comparitable price, i should imagine Gary (iowsr) would be able to tell you how they obtain spares for their stock.

 

Your not planning a Kruger or de Ghlen new build are you?!

 

It would depend also on what it was, for instance, if it was something that you wanted to run on didcots demo line, then you would have to go with vacuum brakes, same as if you wanted to see it used as very few lines have air braked stock

 

Vacuum brake equipment is still available. The hardest bits are vac cylinders which generally come from S. Africa/India. Obviously, air brake equipment is available. Any decision would need to take into account a lot more than simple availability based on this fact.

 

starting from scratch. Outside factors do not apply (other perhaps aesthetics)

 

If outside factors do not apply, the choice must be purely personal. Which do you like most?

 

not a factor. Not my decision, which is cheapest and /or easiest

 

In principle, fitting a vacuum system to a steam loco is much easier than fitting air brakes and probably cheaper. However, you can then qualify that by asking if the loco is going to be steam braked, or what? If it's a diesel, the answer would probably be different, again. Your basic question is far too vague to give a sensible answer to.

 

It is fairly common place to think of air brake equipment as being fairly modern,, most of our equipment was passed down from coach to coach as the Southern Railway upgraded from 4 wheelers to LCDR bogie coaches to SECR/LBSCR coaches. Most of the air brake equipment on the IOWSR is the original from steam days, thankfully their was enough foresight in the early days to purchase plenty of spares. The majority of our 4 wheelers and 2403 (bogie coach) are fitted with original IOW air brake equipment. The triple valves that we use are of the original mechanical type, of which we managed to obtain a few more from Australia a couple of years ago.

 

the entire rolling stock would be either air or vac. starting from scratch. steam diesel rolling stock.....everything

 

I can't comment from the choice at the Loco end but, Vac requires 2" dia steel piping. What would be the 'set up' costs for bending/threading, etc, not to mention the costs of elbows/couplers and suchlike?

On the other hand, Air uses a smaller dia copper pipe. More malleable and therefore easier to route.

Coming from a background in Road Transport, it took me a long time to 'get my head around' Vac systems. A DA valve on Vac provides a similar function to an RE valve on an Air system.

Air, on the other hand, is far more logical and the components tend to be smaller, and lighter in weight. 'Purchase' costs might be greater but 'tooling' costs would probably be less.

Without going back to my old College notes, which are in the loft, I seem to remember (vaguely) that Road Vehicles 'toyed' with using Vacuum back in something like the 60's or 70's but the idea was soon abandoned.

 

More than toy with them. A number of models of buses and lorries had vac brakes. Difference with road vehicles was that they were simple vac. Suck to put brakes ON.

It depends on the size of the vehicle as well. The question doesn't state gauge/scale. If std gauge the answer is probably air, but if 7 1/4" then probably vac as the components are simpler to make (up to a point). Question is still too vague I think to be able to be helpful.

 

In his book 'Swindon Steam' Cook talks about a committee set up by the CMEs to compare Westinghouse air brakes and vacuum.
To try and summarise, he says that *at that time*
the capital cost of air brakes was greater than vacuum
the air brake used less steam than standard vacuum brakes, but slightly more than the GWR vacuum brake at 25in (they built a special rig to measure the effective power consumption of the gwr crosshead pump)
the vacuum brake could have a brake application reduced as desired by a partial release whereas the air brake had to be completely released and reapplied
the air brake had a quicker release and propagation down the train
the vacuum brake required much larger cylinders
I have no idea how much of that is still valid, but I am quite sure others here do know.

 

Certainly the Westinghouse brake with triple valves on rolling stock doesn't allow a graduated release but modern British practice using distributors does allow a graduated release in the same way as the vacuum brake. The problem with triple valves is that, after the brake is released, it takes some time to recharge the auxiliary reservoirs from the train pipe and until they are fully charged the next brake application will need a greater reduction in the train pipe pressure for a similar brake application. Eventually, if the brake is mismanaged, the inevitable happens and there is no air left in the auxiliary reservoirs to enter the brake cylinders. So, if the choice was between a vacuum brake and the automatic air brake as we know it today I would go for air. Airbraked stock with triple valves probably takes greater skill to handle properly but most Southern motormen could fly into platforms and stop on a sixpence with it..

 

thanks for all the replies. This info seems to me to make air brake a no-brainer, with truck equipment available off the shelf and much easier to fit.

 

Taking a simple view, air brakes are usually easier to fault find as air leaks are easier to locate than vacuum leaks. You can use also simple, commercially available test points all over the place. You can also test the system from a remote air supply (compressor). You can spec air systems straight out of a catalogue (I had to do this as an exercise at college many years ago).

 

You have not said what you want it for in enough detail to give a proper answer. Is it for standard gauge passenger hauling or a miniature railway in your back garden? Do you need it to fail safe? What sort of stopping distance is acceptable? Are you running a long distance or running round frequently? Are there any space constraints on the vehicle?

 

It doesn't help the OP one iota but this query reminded me of one of the wonderful David L.Smith's articles where he said he preferred the gentle sigh of the vacuum brake (I.e. Glasgow and South Western) to the harsh hissing of the Westinghouse (I.e. Caledonian), both being available for comparison at Carlisle Citadel.

Dave

 

Interesting, I've heard the opposite opinion expressed by people familiar with parts of the SR where the air and vacuum came together, where the gentle panting of a Westinghouse pump being soothing in a way that the whistly-roar of a vacuum ejector isn't.

With regard stopping, it was always reckoned that the air brake gave much more precision, which was useful in a dense suburban network where running quickly and precisely into a platform was at a premium. Indeed, in the 1950s when the Brighton tank engines were widely phased out, those ex-LBSCR men west of the Brighton mainline who were lumbered with Drummond M7s in compensation found them pretty agricultural in comparison to the Stroudley and Billinton tanks they had grown up with. At least those east of the Brighton mainline given Wainwright H's had something with a bit more finesse, even if they still had to make do with vac brakes!

And none of that helps the OP one iota either!

Tom