Air brakes on loco hauled services

[ryan125hst]

Having enjoyed looking at some photos of loco hauled trains in the BR Blue era of the 70's and 80's over the last couple of days (all before my time sadly- if only it were possible to go back in time so I can experience those days!), I started looking into a few technical aspects, being the technically minded person I am. One such thing was the brakes and, surprisingly, the answer to my question can't be found online or by watching videos as I thought it would be.

From what I can gather, modern DMU and EMU traians use the EP (or electro-pneumatic) brake which allows the brake to be applied and released faster and allows the brake to be applied along the train at the same time. Loco hauled trains, however, such as the Deltics and Class 47 features in the photographs on Flickr that I found, would have had the two pipe air brake. This was better than a one pipe system as the auxiliary reservoirs on the train are filled from the main reservoir pipe, meaning that the auxiliary reservoirs on each carriage are filled faster so there is no risk of them running out of air and leaving the train without brakes.

One downside to the air brake system compared to the older vacuum brakes, from what I have read, is the lack of ability to partially release them. You can partially apply them, but to release them requires a full release. EP brakes don't have this issue, but the old system is overlaid and used in the event of a EP failure from what I understand (please correct me if I am wrong).

The question I have is was this lack of a partial release present on the loco hauled trains of the 70's and 80's? If that is the case, could someone explain the technique of braking, say, an 11 coach train on the ECML to a stand at a platform. I understand that brake controllers would have had the positions: Release, Running, Lap, Initial, Service, Full Service and Emergency. Would full service have been selected to reduce speed initial before releasing the brakes and selecting a lower brake rate to ease the train into the station? Or would a lower brake position normally have been used (I think it can be increased continuously between initial and full service?).

Finally, both videos I have seen mention reducing the brake shortly before the train stops, either by releasing the brake on an EPB, or by reducing to step 1 on a Class 321, as this removes the jolt that would be felt by passengers otherwise as the brakes are releasing as the train comes to a stop. The brakes are obviously then reapplied to keep the train at a stand. Would a similar technique have been used on loco hauled trains or would it have taken too long or the brakes to respond, particularly on long trains of 11 coaches or more?

 

[dubscottie]

Its a bit late for a long answer but the 2 pipe system (reservoir pipe and control pipe) is used on passenger stock so that should the train split, both parts will come to a halt.

I know on the ScotRail push pull 47/7 services drivers would often do the final braking and hold the train in the station using only the loco brake especially if they had one of the tread brake DBSO's on a rake of disc brake Mk2/3's.

Its all about driver technique.

 

[ryan125hst]

the 2 pipe system (reservoir pipe and control pipe) is used on passenger stock so that should the train split, both parts will come to a halt.

I could be wrong, but I thought that this feature existed on the one pipe system as well, and on the the vacuum brake?

 

[Flying_Turtle]

I could be wrong, but I thought that this feature existed on the one pipe system as well, and on the the vacuum brake?

Also, with one pipe air brakes you can make partial releases, at least on continental stock. This kind of stock has an auxiliary reservoir which is filled when the brake pipe is at 5 bar and which will provide the braking power in the case of an emergency braking/split train. This auxiliary reservoir will also place air into the pipe if it senses a quick release (detected mechanically bya sudden rise in the brake pipe pressure).

In practical terms you can have an ep rake coupled to a dual pipe rake in its turncoupled to a single pipe brake without no problems whatsoever.

As a side note: the AAR freight brake indeed does not allow partial releases.

 

[coppercapped]

One downside to the air brake system compared to the older vacuum brakes, from what I have read, is the lack of ability to partially release them. You can partially apply them, but to release them requires a full release.

In the original incarnation of the straight air brake George Westinghouse used a device called the triple valve on each vehicle to control application and release. This indeed did not permit graduated release but more modern applications, and used on all BR systems since the it moved from vacuum to air brakes, use a 'distributor' rather than a triple valve and this permits graduated release. See http://http://www.railway-technical.com/air-brakes.shtml#Distributors for more details.

 

[Jonfun]

I could be wrong, but I thought that this feature existed on the one pipe system as well, and on the the vacuum brake?

In most circumstances yes it would, though failure conditions do exist for both single piped air and vacuum brakes whereby it may not. The two pipe system uses a second pipe (main reservoir pipe) to continuously fill the auxiliary reservoirs which would safeguard their correct operation in stopping the train if it split.

 

[flash]

Vacuum braking systems had several variants, one of which was AFI (Accelerated Freight in-shot), all systems allowed for the partial release of brakes. AFI was disliked by drivers as the train would automatically augment the brake application... causing difficulties stopping short. DMU's had a vacuum reservoir pipe (how that worked I don't know as never signed them!)

Air brakes, there were 4 variants that allowed partial release of brakes, single piped, 2 piped, EP and Westcode. Vehicles (Coaches or wagons only) that were fitted with a triple valve would not allow partial release of the brakes when operating on a single pipe or 2 piped system. Triple valve fitted vehicles were in the main EP multiple units and continental wagons.

All systems would stop the train in event of a train division

 

[AndrewE]

for more details.

Unfortunately can't access this.
A

 

[coppercapped]

Unfortunately can't access this.
A

Sorry, I'll copy it again.

http://www.railway-technical.com/air-brakes.shtml#Distributors

 

[Kneedown]

I've worked air braked freight and passenger, twin and single piped.
Most air braked wagons and coaches (certainly when I worked them) used a distributor to send air to the brake cylinders and you could certainly apply and partially release. You could do that for as long as there is sufficient air in the main res. Continental wagons though, tended to be fitted with triple valves instead of a distributor, and I believe it was not possible to partially release these. The only triple valve wagons I ever had on my trains were in formations of UK distributor fitted wagons so, fortunately, I never had any scary moments. Even so you would get a warning on the TOPS sheet of the presence of triple valves.

 

[Spagnoletti]

DMU's had a vacuum reservoir pipe (how that worked I don't know as never signed them!)

The Vac reservoir on a DMU, AIUI, is to allow the brakes to be released quickly when pulling away from a standing start. This is because the exhauster is mechanically driven from the engines so will not be running at full speed when the unit is at a stand.

 

[physics34]

Have driven CIGs and VEPS on just Westinghouse brake.......( we used to do it on ECS movements as standard), and i must say what an interesting concept the triple valve is. Took me ages to understand in the school! Much easier when you are physically using it.

 

[headshot119]

The Vac reservoir on a DMU, AIUI, is to allow the brakes to be released quickly when pulling away from a standing start. This is because the exhauster is mechanically driven from the engines so will not be running at full speed when the unit is at a stand.

Actually it was designed to allow a quicker release of the brakes under all circumstances. It works by having a reservoir at 29-30 inches of Vac, which allows the release pipe which is around 25 inches of Vac to be "filled" with Vac quicker, rather than exhausting it via the exhausters.

The exhausters only run when the the unit is in neutral, and therefore will be running at full whack when the unit is at a stand.

 

[ryan125hst]

Thanks for your replies. So partial releases are available on UK loco hauled coaching stock. That must make them far easier to drive. Having to do a full release every time must be far more difficult, and the concept of a triple valve sound slightly concerning to me when you only have a few brake applications before you run out of air!

 

[ryan125hst]

I've got another question on this subject if you don't mind

What's the technique for braking a loco hauled passenger train, lets say a 13 coach train hauled by a Class 47? Would they apply the brakes to the full service position to reduce speed, then reduce the brake force once a certain speed was reached before increasing and decreasing the brake to allow the train to stop in the correct position? Or would the initial application be used to reduce speed with the high application rates being used to reduce speed quicker if the train is still going too fast, or would it be somewhere between this?

Additionally, how would this vary for different length of train, ie for a 13 coach train vs an 8 coach train vs a 4 coach train say. And would this vary again if the train was vacuum braked instead of air braked?

Finally, I've seen it mentioned that it's best for the train to stop with the brakes being released to prevent the train from jolting. Would this be a total release or would they put the lever into the initial application position just before the train comes to a halt for this purpose?

 

[flash]

I've got another question on this subject if you don't mind

What's the technique for braking a loco hauled passenger train, lets say a 13 coach train hauled by a Class 47? Would they apply the brakes to the full service position to reduce speed, then reduce the brake force once a certain speed was reached before increasing and decreasing the brake to allow the train to stop in the correct position? Or would the initial application be used to reduce speed with the high application rates being used to reduce speed quicker if the train is still going too fast, or would it be somewhere between this?

Additionally, how would this vary for different length of train, ie for a 13 coach train vs an 8 coach train vs a 4 coach train say. And would this vary again if the train was vacuum braked instead of air braked?

Finally, I've seen it mentioned that it's best for the train to stop with the brakes being released to prevent the train from jolting. Would this be a total release or would they put the lever into the initial application position just before the train comes to a halt for this purpose?

It depends.... with EP braked trains I was trained to make a full brake application then release the brake in stages to achieve a smooth stop - this was in the 80's, its a different regime today, with 'ordinary' air brakes, again I was trained to use an initial application first and then once the brakes were biting make further applications as necessary - even using full service braking if your confidence allowed, releasing the brakes as the train came to a stand, ideally with practically nothing in the brake cylinders as the train stopped, swiftly followed by applying the loco brakes.

Today I work on the principle of one brake application, and release the brakes as the train comes to a stand, but that comes from many years with the same TOC and traction.

 

[ryan125hst]

It depends.... with EP braked trains I was trained to make a full brake application then release the brake in stages to achieve a smooth stop - this was in the 80's, its a different regime today, with 'ordinary' air brakes, again I was trained to use an initial application first and then once the brakes were biting make further applications as necessary - even using full service braking if your confidence allowed, releasing the brakes as the train came to a stand, ideally with practically nothing in the brake cylinders as the train stopped, swiftly followed by applying the loco brakes.

Today I work on the principle of one brake application, and release the brakes as the train comes to a stand, but that comes from many years with the same TOC and traction.

I see, so for normal loco hauled brakes you would go to initial application first and then increase and decrease as necessary to get the train to stop where you want it to stop. For EP brakes, a full application is preferred and then release them step by step, presumably applying them more if it is decided the train wasn't going as slow as expected.

What is the reason that loco hauled trains are held on the loco's brake only and not on the train brakes? Is it for a quicker release?

Presumably modern rolling stock, including HST's and 225's, don't have this option so are held on their train brakes instead?

 

[axlecounter]

I presume the reason is for a fast release, so to avoid to give power with braked carriages, but also for fast braking, since you're supposed to stop the train while releasing the train brakes. It would take a certain time for the train brakes to apply fully after this release, while the loco brakes will always apply immediately.

It can be different if you must stop on a slope where the loco brakes aren't enough to hold the train (mostly happens with freights). In that case you will have to stop with the train brakes applied, choosing the necessary braking force to hold the train.

Modern rolling stock usually has only EP train brakes.

 

[ryan125hst]

I presume the reason is for a fast release, so to avoid to give power with braked carriages, but also for fast braking, since you're supposed to stop the train while releasing the train brakes. It would take a certain time for the train brakes to apply fully after this release, while the loco brakes will always apply immediately.

It can be different if you must stop on a slope where the loco brakes aren't enough to hold the train (mostly happens with freights). In that case you will have to stop with the train brakes applied, choosing the necessary braking force to hold the train.

Modern rolling stock usually has only EP train brakes.

That's a good point axlecounter as it has got to be the quickest way to provide some sort of brake to the now stationary train once it has stopped with the brakes releasing. EP braked stock would be a lot easier as it's all controlled electronically so would respond quicker I'd guess. That makes sense for the freight trains as well.

Speaking of freight, I see that most freight trains in the UK are single piped. How does that affect driving technique as this would mean that the danger of running out of air is present, yet surely our freight trains have to apply the brakes more often than the freight trains of, say, America?

 

[Phil.]

I presume the reason is for a fast release, so to avoid to give power with braked carriages, but also for fast braking, since you're supposed to stop the train while releasing the train brakes. It would take a certain time for the train brakes to apply fully after this release, while the loco brakes will always apply immediately.

It can be different if you must stop on a slope where the loco brakes aren't enough to hold the train (mostly happens with freights). In that case you will have to stop with the train brakes applied, choosing the necessary braking force to hold the train.

Modern rolling stock usually has only EP train brakes.

I hope not. E.P. brakes are not automatic. I rather think that you're thinking of the Westcode brake.

 

[ryan125hst]

I hope not. E.P. brakes are not automatic. I rather think that you're thinking of the Westcode brake.

The way I understand it is the EP brake is used as the main service brake and the only connection running the length of the train is the main reservoir pipe (you can see this on the BSI couplings of Pacers and Sprinters for example). The braking is controlled through the use of several wires in the electrical connection of the coupler. I think the service braking is controlled by three wires but there's also a wire that effectively replaces the automatic air brake pipe. If this wire isn't at the required voltage (I don't know what voltage it's normally kept at), then the emergency brake will apply.

Hopefully someone will come along and explain in more detail

 

[MisterT]

I guess it's not that different from the Netherlands:
Normal air brakes should be available as back up (in case of an e.p. brake malfunction or a malfunction of the dynamic/rheostatic brake (or how do you call it in the UK?)) and an emergency brake application will always trigger the normal air brake too.

 

[axlecounter]

I hope not. E.P. brakes are not automatic. I rather think that you're thinking of the Westcode brake.

I was actually thinking of something in between. I best know braking systems of non-UK countries (mostly Switzerland and Italy) and here the Westcode system isn't used. Rather a system that we call "EP brake" is in use.
That is: there still is the traditional brake pipe that acts just like in Westinghouse's system but braking, in normal operation, is obtained by an electrical cable that either
a) tells the distributors how much air to put into each brake cylinder or
b) tells electrovalves fitted on each carriage how much to reduce the pressure in the brake pipe.

This are called respectively direct and indirect EP braking systems. They are used on traditional rolling stock but on EMUs too.

If I understood the Westocode system correctly, a brake pipe isn't used anymore but rather an air pipe that just provides air for the brakes and these are electrically driven. This means that when a train gets separated, with the first system, the brakes are applied because air leaks from the brake pipe, while with the second, brakes are applied because the electrical connection is lost. Am I right?

 

[coppercapped]

I was actually thinking of something in between. I best know braking systems of non-UK countries (mostly Switzerland and Italy) and here the Westcode system isn't used. Rather a system that we call "EP brake" is in use.
That is: there still is the traditional brake pipe that acts just like in Westinghouse's system but braking, in normal operation, is obtained by an electrical cable that either
a) tells the distributors how much air to put into each brake cylinder or
b) tells electrovalves fitted on each carriage how much to reduce the pressure in the brake pipe.

This are called respectively direct and indirect EP braking systems. They are used on traditional rolling stock but on EMUs too.

If I understood the Westocode system correctly, a brake pipe isn't used anymore but rather an air pipe that just provides air for the brakes and these are electrically driven. This means that when a train gets separated, with the first system, the brakes are applied because air leaks from the brake pipe, while with the second, brakes are applied because the electrical connection is lost. Am I right?

Essentially - yes! The Westcode system controls the output air pressure in fixed steps from a constant input air pressure supplied to its control unit by operating different sized diaphragm valves. By energising and de-energising three control wires in principle eight different steps can be achieved - each wire can have two states, on or off, so two to the power of three gives eight.

When used for braking control all three wires being energised gives brake release, and all three de-energised, either by the brake controller or because the train has parted, gives the emergency step. Six graduated levels are possible in between but in multiple unit applications this number has been reduced by simply not using some wire combinations.

Westcode units are used to control the brakes in HSTs. Although the coaches use conventional two-pipe air brakes in order to speed up the propagation of the pressure change in the brake pipe, the driver's brake valve operates two Westcode units, one in each power car. This means that the brake pipe pressure is changed at both ends of the train at the same time so speeding up the application at the rear of the train.

The Westcode control system was also used in the HSTs as originally built to supply switched levels of air pressure to the diesel engine power control governor.

 

[edwin_m]

If I understood the Westocode system correctly, a brake pipe isn't used anymore but rather an air pipe that just provides air for the brakes and these are electrically driven. This means that when a train gets separated, with the first system, the brakes are applied because air leaks from the brake pipe, while with the second, brakes are applied because the electrical connection is lost. Am I right?

I understand there is also a pressure switch on each vehicle so the brakes get applied (using the air in the local reservoirs) if the pressure in the brake pipe falls too low. This protects against various faults that might result in the electrical side working OK but no air available.

 

[Flying_Turtle]

Lets put it like this, assuming a conventional brake arrangement:

A train only needs a functional brake pipe to have its brakes working properly. You can speed up the brake release by adding a 2nd pipe, the feeding pipe. You can further make the brakes act simultaneously in all vehicules by adding an electrical line, thus getting the ao called EP brake. Now:
- The EP brake needs a two pipe braking system
- If the EP fails, you will have a two pipe brake
- If the feeding pipe fails you will have a single pipe brake
Obviously there are itsy bitsy endless details (like most trains need the feeding pipe for the air suspension ) but this is as simple as it gets

 

[whoosh]

Westcode units are used to control the brakes in HSTs. Although the coaches use conventional two-pipe air brakes in order to speed up the propagation of the pressure change in the brake pipe, the driver's brake valve operates two Westcode units, one in each power car. This means that the brake pipe pressure is changed at both ends of the train at the same time so speeding up the application at the rear of the train.

It does use both Brake Control Units (A Davies & Metcalfe E70, or a Westinghouse DW2) to apply the train's brakes (front and rear power cars), however, only the leading power car's Brake Control Unit releases the brakes.

 

[ryan125hst]

There's more information about the EP brake here: http://www.railway-technical.com/ep-brakes.shtml

It is more relevant to multiple units though. I get the impression that HST's and Intercity 225's use an EP system only to apply the brake from the back of the train at the same time as the front so as to speed up the application. The coaches are braked using the normal two pipe air brake system.

 

[coppercapped]

There's more information about the EP brake here: http://www.railway-technical.com/ep-brakes.shtml

It is more relevant to multiple units though. I get the impression that HST's and Intercity 225's use an EP system only to apply the brake from the back of the train at the same time as the front so as to speed up the application. The coaches are braked using the normal two pipe air brake system.

This is what whoosh and I have both posted. Except that the the Westcode system is not the same as a common EP brake.

 

[MisterT]

We use that Westcode system on some units in the Netherlands. I took some pictures from the driver display from a VIRM-6 double deck EMU.
The control wires are called 'treindraden' in Dutch.

Braking steps 1/7 to 7/7:














The last step is a full brake application, not the emergency brake.
Usually only the first two, maybe three brake steps are used in everyday use.