Air Brake Types

paxman · 8 Dec 2019

Hi everyone

I'm curious about the use of single-pipe air brakes on passenger trains around the world.

I recently qualified as a driver on a passenger fleet that's a mix of modern DMUs with EP braking and older diesel-hauled stock equipped with 26L, A-7 and No. 4 single-pipe air brakes. Knowing little about railways, I had assumed that this was the standard everywhere. Apparently I was wrong.

The bother with single-pipe air brakes, of couse, is that your train ends up unbraked whenever you re-charge the brake pipe. In the course of a station stop on my network, this happens twice - once when going from line speed (75mph/120kph) to platform speed (20 mph/30kph), then again from platform speed to stop. Each re-charge takes between 10 and 20 seconds depending on compressor power and train length.

I now understand that single-pipe air brakes are no longer used on UK passenger trains. That said, are they used elsewhere in Europe? I was recently in China and even over there diesel-hauled passenger trains seem to enjoy some form of graduated braking. But I can't imagine that every country in Europe has been able to make that sort of investment.

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hexagon789 · 8 Dec 2019

paxman said:
Hi everyone

I'm curious about the use of single-pipe air brakes on passenger trains around the world.

I recently qualified as a driver on a passenger fleet that's a mix of modern DMUs with EP braking and older diesel-hauled stock equipped with 26L, A-7 and No. 4 single-pipe air brakes. Knowing little about railways, I had assumed that this was the standard everywhere. Apparently I was wrong.

The bother with single-pipe air brakes, of couse, is that your train ends up unbraked whenever you re-charge the brake pipe. In the course of a station stop on my network, this happens twice - once when going from line speed (75mph/120kph) to platform speed (20 mph/30kph), then again from platform speed to stop. Each re-charge takes between 10 and 20 seconds depending on compressor power and train length.

I now understand that single-pipe air brakes are no longer used on UK passenger trains. That said, are they used elsewhere in Europe? I was recently in China and even over there diesel-hauled passenger trains seem to enjoy some form of graduated braking. But I can't imagine that every country in Europe has been able to make that sort of investment.

BR introduced the twin-pipe air brake in 1965 on Freightliner freight trains, it then became the standard for all new passenger coaches. However BR decided for cost reasons to switch to the single-pipe air brake for freight from the early 1980s, the benefits not being as significant for freight.

For passenger services where the performance is needed, they retained the twin-pipe. However, the single pipe system used on freights is fully graduable, using distributors rather than triple-valves.

I believe all of Western & Central Europe and likely much of Eastern Europe even, uses the standard UIC twin-pipe air brake for passenger coaches, not sure about freight.

paxman · 8 Dec 2019

Thanks for your comprehensive reply, hexagon789. In hindsight I should have mentioned the term 'triple valve', which is what our single-pipe air brake systems are based on - and which is why we lack graduated braking on those trains.

It sounds as if Westinghouse's triple valve, or at least earlier versions of it, isn't too common these days in Europe. I gather from your post that it's long been extinct in the UK.

hexagon789 · 8 Dec 2019

paxman said:
Thanks for your comprehensive reply, hexagon789. In hindsight I should have mentioned the term 'triple valve', which is what our single-pipe air brake systems are based on - and which is why we lack graduated braking on those trains.

It sounds as if Westinghouse's triple valve, or at least earlier versions of it, isn't too common these days in Europe. I gather from your post that it's long been extinct in the UK.

It's complicated as Britain initially more favoured the vacuum in the early days of a continous brake becoming compulsory, but some companies did use the Westinghouse air. Going into the 1923 grouping into 4 large companies from many, the vacuum brake became the standard with much of the previous air braked or dual braked being converted to vacuum. Some commuter operations remained air, such as the "Jazz Lines" out of London Liverpool Street and the Southern Railway used it on its electric multiple units. The main reasons for preferring the vacuum were it being cheaper, easier to set-up with steam locos and the ability to graduate release was seen as preferable for Britain's generally faster trains.

Going into BR days, the vacuum was the norm for loco-hauled coaching stock, but the Southern Region retained the Westinghouse air for its new Diesel-Electric and Electric Multiple units (EMUs) and it was also used on EMUs on other regions such as the Scottish Class 303, in each case supplanted by Electro-Pneumatic control.

The Southern Region EMUs with Westinghouse single-pipe air brakes lasted majoritally until 2005, but a unit (4-VEP type) was kept for the Lymington branch until 2010. The DEMUs (known as Thumpers from the Engine noise) lasted until 2004 and my own local 303s lasted until 2002.

Each of these used the Westinghouse single-pipe air brake with EP control. The EP was fully graduable in application or release, the automatic air graduable as you know in application only.

Normal practice was to run passenger service on the EP, but Empty Coaching Stock on the Automatic Air to retain competence in using it.

I believe therefore the ex-Southern Region 4-VEPs would be the last passenger trains using the Westinghouse single-pipe air brake in the UK.

Kneedown · 9 Dec 2019

hexagon789 said:
I believe therefore the ex-Southern Region 4-VEPs would be the last passenger trains using the Westinghouse single-pipe air brake in the UK.

Do the 442's not utilise this system? I remember looking round a "brand new" 442 when it emerged from Litchurch Lane in the late 80's, and was amazed at the EP controller instead of the new Westcode system.

paxman · 9 Dec 2019

hexagon789 said:
It's complicated as Britain initially more favoured the vacuum in the early days of a continous brake becoming compulsory, but some companies did use the Westinghouse air. Going into the 1923 grouping into 4 large companies from many, the vacuum brake became the standard with much of the previous air braked or dual braked being converted to vacuum. Some commuter operations remained air, such as the "Jazz Lines" out of London Liverpool Street and the Southern Railway used it on its electric multiple units. The main reasons for preferring the vacuum were it being cheaper, easier to set-up with steam locos and the ability to graduate release was seen as preferable for Britain's generally faster trains.

Going into BR days, the vacuum was the norm for loco-hauled coaching stock, but the Southern Region retained the Westinghouse air for its new Diesel-Electric and Electric Multiple units (EMUs) and it was also used on EMUs on other regions such as the Scottish Class 303, in each case supplanted by Electro-Pneumatic control.

The Southern Region EMUs with Westinghouse single-pipe air brakes lasted majoritally until 2005, but a unit (4-VEP type) was kept for the Lymington branch until 2010. The DEMUs (known as Thumpers from the Engine noise) lasted until 2004 and my own local 303s lasted until 2002.

Each of these used the Westinghouse single-pipe air brake with EP control. The EP was fully graduable in application or release, the automatic air graduable as you know in application only.

Normal practice was to run passenger service on the EP, but Empty Coaching Stock on the Automatic Air to retain competence in using it.

I believe therefore the ex-Southern Region 4-VEPs would be the last passenger trains using the Westinghouse single-pipe air brake in the UK.

Again, a terrific answer. Indeed, our automatic air brakes permit only a graduable application, not a graduable release, hence the obligation to go unbraked a couple of times per station stop.

Although our DMUs have only a single brake pipe, every car has its own compressor, meaning that the auxiliary reservoirs can be constantly recharged. I can't argue that, from a driver's perspective, EP is more forgiving than a 26L/A-7 automatic air brake. When things are going well, though, I do enjoy the 'feel' for the track that the 26L and A-7 give you. And you know within seconds whether you've misjudged the topography or coupler slack or carriage handling.

You've piqued my interest about the 'Jazz Lines' out of Liverpool Street. I see that LNER has its own forum. I might wander over and see if they have anything interesting to share about the old-style brake equipment.

hexagon789 · 9 Dec 2019

Kneedown said:
Do the 442's not utilise this system? I remember looking round a "brand new" 442 when it emerged from Litchurch Lane in the late 80's, and was amazed at the EP controller instead of the new Westcode system.

No that's correct, 442s do have the Automatic Air/EP system. I'd forgotten about them. Unless there's another class I've missed, it would be the 442s then.

hexagon789 · 9 Dec 2019

paxman said:
You've piqued my interest about the 'Jazz Lines' out of Liverpool Street. I see that LNER has its own forum. I might wander over and see if they have anything interesting to share about the old-style brake equipment.

I can't remember if I read a thread about the 'Jazz Lines' on the LNER forum or another, but if I find the thread I'll link it.

Poppysdad · 9 Dec 2019

The UK multiple unit market went over to Digital EP brakes in the mid 1970's (Westinghouse Westcode [Now KB] and then also D&M [Now Wabtec]) with only heritage multiple unts retaining the brake pipe such as the LD3's EP brake units fitted to the class 442's which of course had been reused from earlier trains. The LD3 brake system on 442's is being replaced with a new analogue EP brake system as part of the traction upgrade. The networker EMU's were the first trains to move away from a digital EP brake system to an Analogue EP brake system albeit still retaining digital train wires. With the introduction of trains such as Junipers, Coradias, Desiros' and Voyagers the train line system became analogue rather than stepped (Digital)

hexagon789 · 9 Dec 2019

Poppysdad said:
With the introduction of trains such as Junipers, Coradias, Desiros' and Voyagers the train line system became analogue rather than stepped (Digital)

So that's why those trains have fully variable braking rather than 'stepped', fixed-braking rates

big all · 9 Dec 2019

paxman said:
Again, a terrific answer. Indeed, our automatic air brakes permit only a graduable application, not a graduable release, hence the obligation to go unbraked a couple of times per station stop.

Although our DMUs have only a single brake pipe, every car has its own compressor, meaning that the auxiliary reservoirs can be constantly recharged. I can't argue that, from a driver's perspective, EP is more forgiving than a 26L/A-7 automatic air brake. When things are going well, though, I do enjoy the 'feel' for the track that the 26L and A-7 give you. And you know within seconds whether you've misjudged the topography or coupler slack or carriage handling.

You've piqued my interest about the 'Jazz Lines' out of Liverpool Street. I see that LNER has its own forum. I might wander over and see if they have anything interesting to share about the old-style brake equipment.

Unless things have changed since 1994, 'unbraked' is the wrong term; on Westinghouse systems you have perhaps three goes at around 20psi on a SUB or VEP unit, before the auxiliary reservoir runs out even, then back to application, then drop the DSD will give you a holding application, but you never get anywhere near that position unless you are a very slow learner.

If you are in release (and charge) position, the brake will still fully function by reducing the brake pipe to below the point the triple vale is at.

In other words application reduced to 62psi you release and it charges to 65 psi before you need a further application. It just needs to drop slightly below the level on the other side off the diaphragm to start an application, providing you haven't emptied the aux res.

Poppysdad · 9 Dec 2019

hexagon789 said:
So that's why those trains have fully variable braking rather than 'stepped', fixed-braking rates

Not in all cases stepped digital brake train wires were retained on the Electrostars

hexagon789 · 9 Dec 2019

Poppysdad said:
Not in all cases stepped digital brake train wires were retained on the Electrostars

Because the Networkers have 3-step brakes and it's easier for drivers not having to deal with many different braking systems?

Poppysdad · 10 Dec 2019

hexagon789 said:
Because the Networkers have 3-step brakes and it's easier for drivers not having to deal with many different braking systems?

The growing trend is towards Analogue control of brakes and traction or steps of analogue control, if that is not illogical

The original stepped digital systems had wires running the length of the trains which were energised or de-energised in a greycode sequence to provide steps of braking either 3 or 7 step. Both EMU's and DMU's used this form of trainwire control in the UK with 3 step braking (+ latterly enhanced emergency) 7 Step control was used on LUL and in markets such as Hong Kong, Korea, Taiwan and Australia

The 7 step sequence was also used by some passenger or mixed operation locomotives to provide 7 step control of brake pipe with time dependant stepless control of the brake pipe being used on freight locomotives , this of course relates to locomotives having EP control the brake pipe as opposed to the use of a drivers brake valve

Analogue EP brake systems have also been around for a long time with trainlined demands via signals such as PWM proving analogue control at train and a car level i.e stepless , originally used on metro systems such as LUL, SMRT Hong Kong MTRC etc

With respect to Analogue EP Control on car level then this has a lot of advantages particularly allowing continuous blending with electric brakes, hence the reasons why when traction systems are upgraded then generally this brake system is upgraded at the same time

Stepped braking has been provided even on trains with analogue PWM train control where detents have been provided on the drivers master controller , thus you get stepped levels of PWM

hexagon789 · 10 Dec 2019

Poppysdad said:
The growing trend is towards Analogue control of brakes and traction or steps of analogue control, if that is not illogical

The original stepped digital systems had wires running the length of the trains which were energised or de-energised in a greycode sequence to provide steps of braking either 3 or 7 step. Both EMU's and DMU's used this form of trainwire control in the UK with 3 step braking (+ latterly enhanced emergency) 7 Step control was used on LUL and in markets such as Hong Kong, Korea, Taiwan and Australia

The 7 step sequence was also used by some passenger or mixed operation locomotives to provide 7 step control of brake pipe with time dependant stepless control of the brake pipe being used on freight locomotives , this of course relates to locomotives having EP control the brake pipe as opposed to the use of a drivers brake valve

Analogue EP brake systems have also been around for a long time with trainlined demands via signals such as PWM proving analogue control at train and a car level i.e stepless , originally used on metro systems such as LUL, SMRT Hong Kong MTRC etc

With respect to Analogue EP Control on car level then this has a lot of advantages particularly allowing continuous blending with electric brakes, hence the reasons why when traction systems are upgraded then generally this brake system is upgraded at the same time

Stepped braking has been provided even on trains with analogue PWM train control where detents have been provided on the drivers master controller , thus you get stepped levels of PWM

In other words it's a complicated and varied rather than having been homogenised

Poppysdad · 12 Dec 2019

Its evolution , as was the case frrom vacumm to air , from Brake pipe to EP , DC to AC traction

Air Brake Types

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