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Vacuum brakes
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krus_aragon
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Just outside BR, Ireland was using vacuum braked, BR-built MK2 coaches until 2008.
hexagon789
Veteran Member
I believe there were vacuum braked early Mk2s in service until the early 1990s iirc, not sure about Mk1s.
hexagon789
Veteran Member
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hexagon789
Veteran Member
Indeed, the last Mk2D service was on the 31st March 2008.
Except that the OP excluded 1st generation DMUs
hexagon789
Veteran Member
Ah well, I saw the "charters" bit and recalling the Mk2s in the 1990s I was trying to think of anything later and 121s came into mind. Duly scored out.
Journeyman
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Mark 1 and Mark 2 vehicles operated on the North Wales services until the early 2000s - I take it they were all air-braked by then?
Many of these vehicles were fitted with both braking systems, of course.
hexagon789
Veteran Member
I think those Mk2s were all later Mk2a and possibly c which were air brake only from new.
The green-liveried Mk2s used on Kyle line summer workings until 1994 were I believe vacuum braked as they often ran with the converted Class 101 observation car; that would presumably be a contender for last vacuum braked loco-hauled stock?
Edit: the ex-Regional Railways Mk2s seem to be mostly Mk2a and are certainly all air-braked vehicles.
delt1c
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Correct me if I am wrong , but I thought the Mk2D were air brake, want the Mk2A the last dual braked stock
hexagon789
Veteran Member
Mk2a-f were all air brake only from new, the early Mk2 (sometimes coded Mk2z) were vacuum braked as built, so they could run with Mk1s, but some gained air brakes including those used on the Edinburgh-Glasgow shuttles with Class 27s which were equipped with a two-stage air-operated disc brake system with Girling WSP equipment.
Most of those the retained the disc brakes and WSP equipment after the end of the Class 27 shuttles but with the two-stage system isolated; some gave up their disc-braked B4s to the Mk2f DBSOs.
apk55
Member
Last freight using vacuum brakes I think was the ICI hopper wagons (built in the 1820s) from Tunstead (Buxton) to Winnington (Northwich), which lasted until the late 90s
Clarence Yard
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The last everyday vac loco hauled workings around London were the NSE Thames services from Paddington with their Mk1 & 2 sets. They lasted until 1992.
randyrippley
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They must have been the longest-lived railway stock anywhere. 170 years!
hexagon789
Veteran Member
Yes withdrawn December 1997 I believe, though not quite as old as the 1820s!
apk55
Member
Sorry about the typo it should have been 1920s
I do have fond memories as a school kid watching a 8F hauling these wagons. Later they used class 20s and only scrapped because there there suitable equipped locomotives in the area to run the service.
edwin_m
Veteran Member
I was going to post that but the quoted post was referring to the Irish Mk2ds. It was a little odd to my eyes to see vacuum braked container flats in East Wall Yard a few months back, although I think the more recent ones are air-braked.
hexagon789
Veteran Member
Just as well you said that, I had erroneously assumed Delt1c was referring to British ones not the Irish ones.
Just to clarify in case I did indeed misunderstand you:
BR Mk2z; vacuum from new; some later air braked
BR Mk2a-f: UIC two-pipe air braked
NIR Mk2b: Westinghouse 3-pipe air braked from new, later converted to UIC two-pipe when additional ex-BR Mk2s were transferred
CIE/IÉ Mk2D: vacuum braked
IÉ ex-BR Mk2: UIC two-pipe air braked
delt1c
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Built in 1820's, they must have seen some traction during the years lol
Rockhopper
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Whats the advantage of air brakes over vacuum brakes?
edwin_m
Veteran Member
Fundamentally, a vacuum brake works on the pressure difference between the vacuum and the atmosphere, which can only be as much as atmospheric pressure in theory and is less than that in practice. Air can be compressed to many times atmospheric pressure so the working pressure difference can be much greater in an air brake. Since force equals pressure multiplied by area, to provide the same force the pistons in the brake cylinders need to be that much larger in the vacuum system.
Rockhopper
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I see, so the braking force on a vacuum system is produced by a spring effectively and the vacuum hold the brake off whilst in an air brake system its air pressure that produces the braking force? I assume the air brake system fails safe in the same way a vacuum system does?
hexagon789
Veteran Member
Quicker application and release, particularly with long trains; requires smaller/lighter equipment typically.
The main reason vacuum brakes found favour in Britain was it was simpler to employ with steam engines and more importantly vacuum offered graduated release, something the original air brake didn't but which single-pipe systems with distributors or the near universal twin-pipe system used on passenger vehicles now do offer.
hexagon789
Veteran Member
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.
ac6000cw
Established Member
Description of automatic vacuum brakes here - https://en.wikipedia.org/wiki/Vacuum_brake#How_the_automatic_vacuum_brake_works - and basic automatic air brakes here - https://en.wikipedia.org/wiki/Railway_air_brake#Westinghouse_air_brake
They are both only 'fail safe' against the sudden loss of air pressure or vacuum in the 'train pipe' that links all the vehicles together. But that only works if the brake system has been properly 'charged' beforehand (to normal working pressure/vacuum, so that there is something to actually provide the brake force) and that the continuity of the brake pipe has been proven. That is why performing a 'brake test' when a train is being prepared for departure is one of those 'written in blood' rules in the rulebook. If you've got no traction power, it's unfortunate, if you've got no working brakes it could be deadly...
krus_aragon
Established Member
Another punt at explaning the difference, in a slightly layman-esque manner:
Vacuum brakes work by reducing pressure in the brake pipe. Air brakes work by increasing the pressure.
On Earth, the pressure is one atmosphere. You can't get lower than zero atmospheres of pressure (that's a perfect vacuum), so that limits the effectiveness of vacuum brakes to one atmosphere worth of difference.
If you use air brakes instead, there's no such limit when you're increasing pressure (assuming your pipes etc. can withstand it). So you can have two, three, or more atmospheres worth of difference.
This greater difference can result in faster-working brakes, and greater braking force on the wheels.
Vacuum brakes work by reducing pressure in the brake pipe. Air brakes work by increasing the pressure.
On Earth, the pressure is one atmosphere. You can't get lower than zero atmospheres of pressure (that's a perfect vacuum), so that limits the effectiveness of vacuum brakes to one atmosphere worth of difference.
If you use air brakes instead, there's no such limit when you're increasing pressure (assuming your pipes etc. can withstand it). So you can have two, three, or more atmospheres worth of difference.
This greater difference can result in faster-working brakes, and greater braking force on the wheels.
Rockhopper
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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 
ac6000cw
Established Member
That's how 'simple' vacuum or air brakes work - 'automatic' (fail safe) train brakes work the other way round. The actual force to apply the brake shoes/pads to the wheels/discs is provided by *locally stored* compressed air (in each vehicle reservoir) or vacuum (in each brake cylinder). The actual brake pipe along the train is held at high pressure (air) or high vacuum when the brakes are released, and is lowered (air) or raised (vacuum) towards atmospheric pressure to apply them. The amount of brake force applied is proportional to the difference between the 'locally stored' pressure and the new train pipe pressure.
When the brakes are released (i.e. train pipe at high pressure or vacuum), the locally stored air or vacuum is replenished from the train pipe i.e. the train pipe serves a dual purpose in a classic single-pipe braking system.
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edwin_m
Veteran Member
A spring isn't really powerful enough for a brake that can stop a moving train. So as mentioned each coach has a "reservoir" of air or vacuum, and when the train pipe gets closer to atmospheric pressure some fairly complicated valves connect the reservoir to the brake cylinder and the resulting pressure difference applies the brake. The disadvantage with this is that you can't leave a train shut down (or unattended, as the pump might fail) because in a period of a few hours the air/vacuum will leak and there will be no brake force. The big accident at Lac Megantic in Canada was a result of failing to secure a train with hand brakes before leaving it unattended. Modern EMUs get round this by having spring-applied parking brakes but they are only powerful enough to keep a standing train from rolling away if there is no air in the system - a bit like a car hand brake in fact.
Is the daily Jacobite from Ft William to Mallaig, in the timetable, not vacuum braked loco and Mk 1 stock?
Very little stock is dual braked. It is a considerable mechanical nuisance to arrange, and there's generally not enough underframe space for two lots of kit, plus a third lot connecting the two and making the applications balance from either side. Locomotives were different because their "dual brake" only applied to the train brake - the brake on the loco itself was always air only from first diesel days. The Mk 1 restaurant cars etc that ran with Mk 2/3 formations was all converted from one to another.
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.
Very little stock is dual braked. It is a considerable mechanical nuisance to arrange, and there's generally not enough underframe space for two lots of kit, plus a third lot connecting the two and making the applications balance from either side. Locomotives were different because their "dual brake" only applied to the train brake - the brake on the loco itself was always air only from first diesel days. The Mk 1 restaurant cars etc that ran with Mk 2/3 formations was all converted from one to another.
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.
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