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Westinghouse Air Brake?
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Nice to hear a few are still around!
I trained on them and really appreciate the difficulty of using them properly - forever worried about whether your train is bunched or stretched, how hot the brake blocks are getting, when or if to engage the dynamic brake, whether you’ll misjudge the application and go sailing through a signal or platform unbraked.
Westinghouse air brakes really keep you focused on the job because, frankly, they’re so hopeless. (We’re gradually losing them, alas.) I’m sure there’s an equivalent with vacuum brakes in Great Britain.
I trained on them and really appreciate the difficulty of using them properly - forever worried about whether your train is bunched or stretched, how hot the brake blocks are getting, when or if to engage the dynamic brake, whether you’ll misjudge the application and go sailing through a signal or platform unbraked.
Westinghouse air brakes really keep you focused on the job because, frankly, they’re so hopeless. (We’re gradually losing them, alas.) I’m sure there’s an equivalent with vacuum brakes in Great Britain.
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contrex
Established Member
I don't know who told you that in GB 'most locomotives' use vacuum brakes, but I have to tell you they are ancient history!
Now that’s interesting. What sort of brakes do current locomotives use? Is the braking system distributed down the whole consist, such that you can apply and release in a graduated fashion? Or are you still trapped in that infernal Westinghouse conundrum of having to completely release, then recharge, all brakes on the train before being able to make another application?
Some of the trains I drive use Westcode 3 step brakes, which is an electropneumatic system with a brake control unit on every vehicle and others use Davies & Metcalf brakes which are a sort of hybrid EP system with a brake control unit (E70) on the powercars and and air train pipe through to brake distributors on the coaches. With bot types you can partially release or fully release and reapply the brakes as many times as you like, if I've correctly followed what you mean.
I don't know what freight trains use and I've never heard of vacuum brakes.
contrex
Established Member
You should specify if you are talking about loco-hauled freight, and not (e.g.) high or medium speed passenger, or metro passenger.
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Common from about the 1860s in the UK up to and beyond the end of steam. Vacuum brakes have been entirely superseded on the National Rail system in the UK (with the British Rail Class 121 "bubble cars" being the last mainline trains to have vacuum brakes having been withdrawn in 2017). They are still in use on most standard gauge heritage railways and a small and shrinking number of main line vintage special trains.
Vacuum brake - Wikipedia
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Which train was that?
The Chimaera
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You appear to be referring to what we called ’Triple’ Valve’ fitted stock. Not many trains used that system and those that did were mainly EMU’s to my knowledge. It wasn’t popular and was an inferior setup to the more common air brake system with distributors on every vehicle. I believe these trains are long gone.
Westinghouse Air brake systems are still used on some of our older Locomotives but these aren’t Triple Valve systems.
Most modern stock uses Electrically controlled Brake Systems.
Indeed. I had assumed that all Westinghouse air brakes relied on triple valves. It’s a remarkable system given its antiquity (I mean, you’re literally using air to stop a whole train). The downside, of course, is that you can’t make a follow-up brake application till the train’s brake pipe has been completely recharged. Before that point, without the right pressure ratio in the auxiliary reservoir, you’re essentially unbraked.
Do your electrically controlled brake systems allow for graduated braking throughout the train in both directions? So, for instance, if you over-brake, can you partially release until you find the right deceleration? Do they rely on electric motors to apply brake blocks to wheels rather than air pistons?
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Thanks for that useful explanation.You should specify if you are talking about loco-hauled freight, and not (e.g.) high or medium speed passenger, or metro passenger.
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Common from about the 1860s in the UK up to and beyond the end of steam. Vacuum brakes have been entirely superseded on the National Rail system in the UK (with the British Rail Class 121 "bubble cars" being the last mainline trains to have vacuum brakes having been withdrawn in 2017). They are still in use on most standard gauge heritage railways and a small and shrinking number of main line vintage special trains.
Vacuum brake - Wikipedia
en.wikipedia.org
I’m referring to freight and medium-speed passenger services (which for us is around 100mph/160kmh). Our air-braked trains are limited to 80mph/125kmh; faster ones are passenger only and use hydrodynamic systems, with god-awful underframe pulsing that wakes the dead.
So I take it that even lower-speed legacy UK rolling stock - ie stuff that would’ve been in service before 2000 - used a form of distributed electrical braking? Clearly vacuum brakes had long vanished from the mainline before then.
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The passenger trains I drive have disc brakes with pads operated by air via brake cylinders. The control of air into the brake cylinders on each vehicle is controlled by electrical signals so you get almost instant application or release simultaneously on each vehicle. On the three step brake you can go between the steps as much as you need though the manuals and instructors warn against flicking between the steps a lot. Each step gives a fixed rate of deceleration so you usually do need to partially release and reapply a few times when you're stopping at a station. I think newer trains use stepless brakes but it's the same idea, a signal is fed to a control unit which lets air in or out of the brake cylinders. Electric trains use electrical braking but I don't really know anything about that system.
On the other type of train I drive the distributors are fed with air continuously at a fixed pressure by a main reservoir pipe. The pressure difference between the main reservoir side of the distributor diaphragm and the air train pipe side of the distributor diaphragm is what causes the application and release of the brake. Decreasing pressure in the air train pipe applies the brake and raising the pressure in the air train pipe releases the brake. The air for the brake cylinders comes from the main reservoir pipe. The EP bit of this brake is the E70 control unit between the driver's control knob in the cab and the air train pipe. It translates the position of the knob into an air pressure setting for the air train pipe and also sends an electrical signal to the E70 in the other powercar at the back of the train. That allows the pressure to be reduced by the E70 at both ends of the pipe simultaneously which makes the brake apply quicker.
If you had triple braked vehicles in your consist (e.g. continental ferry vans or various MUs hauled dead) and heeded the warnings not to fan the brake, you changed your braking technique to a more graduated application. If you stopped short somewhere, so be it. But these were pre delay mithering days.
contrex
Established Member
EP (electro-pneumatic) braking for multiple units was in use starting on the London Undergrond in the 1920s and mainline from 1950 and is pretty universal now.
Detail here:
Electro-pneumatic brake system on British railway trains - Wikipedia
Hence the 'EP' in EPB, VEP and CEP for Southern Region trains.EP (electro-pneumatic) braking for multiple units was in use starting on the London Undergrond in the 1920s and mainline from 1950 and is pretty universal now.
Detail here:
Electro-pneumatic brake system on British railway trains - Wikipedia
hexagon789
Veteran Member
As in modern Westinghouse made air brake systems or the traditional Westinghouse air brake with triple-valve vs the PBL system used on 66s and many other classes today?
ac6000cw
Established Member
Even electrically controlled friction brakes normally use compressed air to actually force the brake shoes or pads against the wheels or disks.
When continuous train brakes were made mandatory on passenger trains in the UK towards the end of the 19th century, most of the then private railway companies adopted vacuum brakes but some adopted air brakes, meaning some passenger stock and/or locomotives had to be fitted with both type of brake to operate through passenger trains involving multiple railway companies. After the 'grouping' in 1923 into the 'Big 4' companies, the vacuum brake effectively became the de-facto UK standard for loco-hauled passenger and fast freight trains. But electric multiple-unit passenger trains tended to adopt air brakes (for various good reasons, including using compressed air for other purposes on the trains). After nationalisation in 1948, BR continued with the same situation until the early 1960s when it decided to adopt air brakes as the future standard on loco-hauled trains, starting with new-build passenger stock and freight stock plus converting many locos to dual vacuum and air brake capability.
At a very basic level, there isn't - American George Westinghouse invented the automatic train air brake in 1868 and founded the Westinghouse Air Brake Company in 1869. Modern versions (with many enhancements and developments over the intervening 150+ years) are direct descendants from that. The basic principle remains the same - of having a continuous 'train pipe' along the train, maintained (when the brakes are off/released) at high pressure with individual air reservoirs on each vehicle fed from it (via a valve which only allows higher pressure air in), then reducing the pressure in the train pipe to apply the brakes (in proportion to the difference in pressure between the vehicle reservoir and the train pipe).
This is a simple guide to how air brake systems work, which also covers two-pipe systems and 'distributors' (the modern replacement for the original 'triple-valve' that Westinghouse invented) - http://www.railway-technical.com/trains/rolling-stock-index-l/train-equipment/brakes/
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Indeed. One of the first thing driver trainers impressed on us was that you got two bites of the cherry. If that second application was going to cause you to stop short, so be it. Better that than risking a third application.
But of course we all drive now with grey-suited managers breathing down our necks. It’s sadly common to see inexperienced drivers coming in to platforms too hot, then desperately slamming on the air brake to either sail through the other end or lurch to a stop with doors still off and passengers catapulted into the rafters.
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I’ve learned a lot from all your informative replies. Thanks!
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Ta - Still learning myself! It’s all one big mutual improvement class.
Always very interesting. Thank you everybody!EP (electro-pneumatic) braking for multiple units was in use starting on the London Undergrond in the 1920s and mainline from 1950 and is pretty universal now.
Detail here:
Electro-pneumatic brake system on British railway trains - Wikipedia
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