Vacuum brakes

[ac6000cw]

The Southern Railway/Region also had some air brake fitted steam locos used (as far as I know) mostly for moving EMU stock around. I had a brief drive of the tiny ex-LBSCR/Southern/BR 'Terrier' tank "Martello" at Bressingham recently, which is dual (vacuum & air) brake equipped - the characteristic repetitive wheezing noise from the air pump certainly added to the soundscape (the pump is to the right of the cab entrance in the photo below).

Martello - the cab by ac6044cw, on Flickr

 

[hexagon789]

The Southern Railway/Region also had some air brake fitted steam locos used (as far as I know) mostly for moving EMU stock around. I had a brief drive of the tiny ex-LBSCR/Southern/BR 'Terrier' tank "Martello" at Bressingham recently, which is dual (vacuum & air) brake equipped - the characteristic repetitive wheezing noise from the air pump certainly added to the soundscape (the pump is to the right of the cab entrance in the photo below).

Martello - the cab by ac6044cw, on Flickr

The Scottish Region retained some former Caledonian locos with air brakes for the same purpose in the early 1960s - moving its EMU fleet.

 

[Journeyman]

Several pre-grouping railways long ago actually used air brakes rather than vacuum for their steam hauled services, including the Great Eastern and the Caledonian, and these, with their associated stock, lasted in some aspects through to the end of steam just on suburban services. When the first 25Kv electric stock came along around 1960 in both areas these old locos came in handy to move the new air braked emus around, no diesels at the time being capable. For some reason the Southern Railway also converted all the Isle of Wight system to air brakes - if you go to the museum railway on the island it's all air brake old stock and steam locos.

The LBSCR and one of the constituents of the SECR - I forget which - were air-braked systems, so the transfer of air-braked stock redundant on the mainland was the reason the IoW ended up air-braked.

 

[ac6000cw]

Several pre-grouping railways long ago actually used air brakes rather than vacuum for their steam hauled services, including the Great Eastern and the Caledonian,

Out of interest, on the joint Anglo-Scottish passenger services that the LNWR and the Caledonian ran, was any of the passenger stock dual-braked, or did the Caley have some dual-brake equipped locos to haul the trains north of Carlisle?
(I guess the same problem would have existed with handling fast brake-fitted Anglo-Scottish freight trains as well).

 

[hexagon789]

Out of interest, on the joint Anglo-Scottish passenger services that the LNWR and the Caledonian ran, was any of the passenger stock dual-braked, or did the Caley have some dual-brake equipped locos to haul the trains north of Carlisle?
(I guess the same problem would have existed with handling fast brake-fitted Anglo-Scottish freight trains as well).

The West Coast Joint stock was dual-braked, the Caley was an air brake company right up to grouping with many locos being thus dual-fitted under the LMS and retaining their Westinghouse air-brake equipment until withdrawn in the 1960s.

The last pure air-braked CR coaches were the 45-footers, withdrawn in about 1930.

 

[ac6000cw]

Understood and thanks for all the info! When i'm slightly less tired I'll look at the link posted to see how airbrakes work

There is quite a good, relatively easy to understand, explanation of how automatic air brakes work here - http://www.railway-technical.com/trains/rolling-stock-index-l/train-equipment/brakes/ - and for vacuum brakes - http://www.railway-technical.com/tr...x-l/train-equipment/brakes/vacuum-brakes.html

(As an aside, the original inventor of automatic air brakes in 1869, George Westinghouse, set up a company to manufacture the equipment called the "Westinghouse Air Brake Company" - today's 'Wabtec' is a direct descendant from that and is still in the business of railway brake equipment, 150 years later).

 

[edwin_m]

There is quite a good, relatively easy to understand, explanation of how automatic air brakes work here - http://www.railway-technical.com/trains/rolling-stock-index-l/train-equipment/brakes/

(As an aside, the original inventor of them in 1869, George Westinghouse, set up a company to manufacture the equipment called the "Westinghouse Air Brake Company" - today's 'Wabtec' is a direct descendant from that and is still in the business of railway brake equipment, 150 years later).

And a lot of the reason why most of Britain adopted the vacuum brake was apparently to avoid having to pay royalties to a foreigner.

 

[hexagon789]

And a lot of the reason why most of Britain adopted the vacuum brake was apparently to avoid having to pay royalties to a foreigner.

Yet despite the higher costs, didn't the generally poorer companies tend to go for it?

 

[Taunton]

(As an aside, the original inventor of automatic air brakes in 1869, George Westinghouse, set up a company to manufacture the equipment called the "Westinghouse Air Brake Company" - today's 'Wabtec' is a direct descendant from that and is still in the business of railway brake equipment, 150 years later).

O S Nock, longstanding railway author and train performance timer, was Westinghouse UK's Chief Mechanical Engineer, and travelled extensively around the country on business, which is where he got many of his timing logs from. Their offices and works were in Chippenham, although Nock lived in Bath.

 

[Bevan Price]

As a historical aside, ex-GWR steam locos could often produce a "better" vacuum than locos from on other railways. A consequence was that, if there was a loco change involving, for example replacing a GW loco by a LMS steam loco, the latter might not be able to fully release the train brakes, and someone had to manually let a bit of air into the brake pipes before the train could move.

 

[trebor79]

Yes that's right I think GWR used 25 inches of vacuum whilst everyone else standardised on 21 inches.

 

[Ducatist4]

Interesting thread guys, I’ve learnt a lot!
Many years ago during the school holidays my mum used to give us a few ££ to spend in the local book shop. I bought a copy of “Red For Danger” probably because it had a picture of trains on the cover!
I can remember story’s of couplings failing and parts of trains running away and so on. The continuous vacuum brake seems such a good solution to that.
I have to admit that I hadn’t appreciated that air brakes were used instead these days!

 

[etr221]

And a lot of the reason why most of Britain adopted the vacuum brake was apparently to avoid having to pay royalties to a foreigner.

The story I heard was that the Westinghouse salesman went to call on that upstanding man Francis Webb (responsible for such matters on the LNWR - the Premier Line) and they came to an agreement for the LNWR to adopt the Westinghouse brake - at which point the salesman invited Mr Webb out for a celebratory drink - but Mr Webb saw this as corruption, told him to go, the deal was off and the LNWR went for the automatic vacuum brake, an example followed by a lot of other railways.

 

[edwin_m]

I think also it's quite easy to create a vacuum on a steam loco - use some steam to push the air out and let it condense - but air brakes need a separate compressor. Having said that I believe the higher degree of vacuum on GWR locos mentioned above was because they used a pump insted of a steam ejector. Diesels and electrics had to have some kind of pump/compressor for either system and probably used compressed air for other functions anyway. As incidentally did the Mk3 coach for the air suspension, so if Irish had wanted vacuum-braked Mk3s they would have needed a compressor as well as a generator, and an air line down the train.

 

[hexagon789]

As incidentally did the Mk3 coach for the air suspension, so if Irish had wanted vacuum-braked Mk3s they would have needed a compressor as well as a generator, and an air line down the train.

Vacuum operated disc brakes wouldn't be ideal, trying to fix up a system for WSP (pretty much essential with disc brakes) with vacuum would be quite something.

 

[ac6000cw]

The story I heard was that the Westinghouse salesman went to call on that upstanding man Francis Webb (responsible for such matters on the LNWR - the Premier Line) and they came to an agreement for the LNWR to adopt the Westinghouse brake - at which point the salesman invited Mr Webb out for a celebratory drink - but Mr Webb saw this as corruption, told him to go, the deal was off and the LNWR went for the automatic vacuum brake, an example followed by a lot of other railways.

I suspect there was a fair amount of 'not invented here' syndrome at work too, especially in those days of autocratic Chief Mechanical Engineers.

As edwin_m mentions, on steam locos the vacuum brake equipment is pretty simple - normally a large and small steam ejector to create and maintain vacuum in the train pipe - and the vehicle equipment is also simple, so cost differences were doubtless also a factor. And back in the late 19th century, vacuum brakes had sufficient performance for the relatively slow passenger trains of the era.

 

[Monarch010]

They are both fail safe in the sense that a division of the train or leak will aplly the brakes - with air it's the loss of air in the brake pipe; with vacuum it's the loss of the vacuum in the brake pipe, the partial vacuum is what keeps the brakes off.

Both can be defeated though if not properly maintained or connected which is why a brake test is so important.

What does a brake test actually entail?

 

[hexagon789]

What does a brake test actually entail?

Testing the continuity of the brake. The process is a bit different on air vs vacuum braked trains. With vacuum braked trains, the diversions creates a vacuum with the loco, with a full vacuum of 21", the brakes should be fully off.

The guard checks this and then goes to the rear of the train, pulls the vacuum bag off, the vacuum will be destroyed and the brakes come hard on.

The bag is the replaced and the vacuum will be recreated assuming the driver has touched nothing. This proves there is a continuous vacuum from front to rear.

 

[Taunton]

Having said that I believe the higher degree of vacuum on GWR locos mentioned above was because they used a pump insted of a steam ejector. Diesels and electrics had to have some kind of pump/compressor for either system and probably used compressed air for other functions anyway.

Actually GWR steam locos had one of each - they had an ejector, plus a vacuum pump attached to one piston crosshead which allows vacuum to be maintained when running without using steam in an ejector. The vacuum pump is what gives the characteristic "tiff-tiff-tiff" sound of GWR locos when coasting, But as the pump only operates when running it is no use releasing the train brakes before you start, where the ejector can do the full 25" vacuum suck.

Traditional diesels all had two pumps, vacuum for the train brake and air for the loco brake.

 

[Highlandspring]

The apparatus that generates vacuum on a diesel loco is called an exhauster.

 

[Richard Scott]

The apparatus that generates vacuum on a diesel loco is called an exhauster.

And most locos had 2 (a few classes only had 1 - 20s, 44/45/46s spring to mind) - even then they are not as effective at pulling the vacuum brakes off as a steam engine ejector even when the speed up is used.