Train equipment in the past

[Nortube]

From the introduction of the 1938 stock until the arrival of the 1967 stock, there was very little difference between the stocks as far as train equipment learning was concerned and 1938 stock was taught as the basics to cover 1938, 1959, 1960 and 1962 stock (this was later changed to 59 stock after the 38 stock were withdrawn). Any minor differences were covered by the stock trainer when training on the line concerned.

A Guard was also an emergency Motorman. He was expected to help the driver to deal with defects, driving the train while the driver braked from another cab if required etc., plus the Guard would also take over the train and drive it to the next station then out of service to depot should the driver become incapacitated. As a consequence, the Guard had to know a lot about train equipment. As part of the one week train equipment at the school, the Guards had to learn the following electrical circuits:
MG circuit, EP Brake circuit, Control circuit basics and the 630v traction circuit on the train. Drivers also had to learn the Control circuit (motor control and operation) in detail and the Compressor circuit

Also covered on the Guards course were the Main line flow of air, Train line flow of air, Westinghouse brake flow of air.
For Guards, this was a challenge as these were all totally new subjects. For drivers, the one week was mainly a refresher, with just the Compressors and enhanced Control circuit being new. Whilst the Guard was expected to understand the equipment on exam, the driver was expected to be perfect.

The Guard's exam was based on a one week rules and regulations and a one week train equipment course, plus some time spent stock familiarisation with a Trainmen's Inspector (Stock Instructor). The exam was verbal, usually consisting of one examiner and three candidates, and lasted around 2-3 hours. Whilst it could be nerve wracking, the Guard's exam was a fairly relaxed affair, depending on the examiner. The Guard was expected to know most of what he'd been taught and to have an understanding and be able to go through dealing with defects. As long as the Guard didn't kill anyone in the process, they usually passed OK. If they were weak on anything, they may get put back to sit in the class (train equipment or rules and regs as necessary)  for a few days to revise. Failing that, if they failed, they usually went for the Railmen's course and ended up on the station side until they could go forward for Guard again. In the seventies, many Guards dropped out for one reason or another, usually because this was the first time that they're had to work unsocial hours and decided it wasn't worth it. Often 50% of the Guards had left within two months of starting, and perhaps 10 - 20%  dropped out during the training

The driver's exam was different. You felt more confident, but woe betide anybody who wasn't up to scratch. Like the Guard's exam, the driver's exam was verbal, but was much longer and could last all day. There were normally three candidates and the one examiner. You had to keep on your toes. The standard start was to give a scenario to a candidate, such as, "You're motoring along not paying much attention as you've just been trying to light your fag when suddenly you notice the train starts to feel sluggish, what do you do?" The person would then start going through the procedure to follow:
A.T.O. check to begin with, then the examiner would give any necessary symptoms as you went along e.g. "air is OK, you have no MG indicator" and so the  candidate would then carry on with the subsequent checks and dealing with the defect from that point. The other candidates could not relax and had to closely follow what was going on because at any time the examiner could say "right, you carry on from there". If the previous person had made a mistake and you hadn't picked it up, you were in the doo doo!

A favourite of the examiner was to let you carry on, even if you had made a mistake and see how far you got, allowing you to dig yourself deeper and deeper into the pit you were digging for yourself. You had to know everything. It was no good just saying "change the EP brake fuse, it had to be "change the 10A EP brake fuse". Very rarely were you given any leeway unless the examiner thought you knew it but were just making silly mistakes. If you killed somebody during the exam, that was usually it straight away.  Depending on the knowledge of the candidates, the three might be whittled down to two or even just one as the day wore on.

If you were lucky, you might be put back in the class for the rest of the week or, more usually, returned to your depot. Depending on what the examiner recommended, you may be told to "revise and come back for a one day re-exam in a months time" and given feedback on where you were weak, or you would just go back for part or all of the course some time in the future.

I was unlucky (or lucky, depending on which way you look at it). We all sat waiting in the class for the examiners to turn up. One particular examiner had a reputation amongst trainees as being very strict and everyone was hoping it wasn't them when an examiner entered the room. Eventually HE entered the room and called me and two others out saying "you're with me". Off we went to the room. It went something like this. I'm X (I can't remember his name), tel me your names. After we had given our names and he'd ticked them off, that was it. No more pleasantries and the questions began! I noticed that he seemed to be concentrating on the other two and at the morning break sent one of them back to their depot for a retry at a later date. At the end of the morning, the second person was sent back to the class for revision, leaving me all on my own in the afternoon. That is NOT what you want, because you know you are going to be asked everything. Things didn't seem to be going too badly and by the afternoon break he said "OK, that will do" and I thought good, I seem to have got away with it. Then he said "we'll carry on in the morning". It was very rare to have to return and finish the exam on a second day. He said "you're not doing too bad, but you're making some silly mistakes". I returned the next morning and by about eleven he said "you've passed, congratulations" and shook my hand. This was the first time that I'd seen him smile since he'd collected us the day before.

[Nortube]

The Motor Generator circuit (diagram at the end of this post)
The motor generator supplies the 50v DC that is needed for the train's control circuits

There is very little difference to the 38 stock circuit. One difference being the 115vAC supply from the MG (later called a Motor Alternator) to the fluorescent car lighting, another being the Passenger alarm and train radio / P.A. that were added in later years.

Like most of the work on the train equipment course, we had to copy the diagram from the blackboard and draw it into out notebooks. Only after the subject had been covered were we given the hand-outs. To me, this was a better way of teaching rather than the way it seems to be these days where a notebook is purely used for any odd jottings you want to make. Because you're drawing the diagram, it remains embedded in your memory. Forty years on, I can still remember virtually all of the 38 stock equipment we were taught, although I may be a little hazy on a couple of fuse ratings.

You drew the diagram and coloured in the feeds from the main fuses. That way you could instantly see what equipment would be affected if that fuse blew. When out on a train and had a defect, I could instantly visualise the diagram. The same goes for other defects. Other drivers have said the same thing.

As a driver you could change most fuses. The MG output fuse, battery fuse, main lighting fuse and auxiliary fuses weren't accessible and so couldn't be touched. It was generally taught that you only changed the fuses that were located in the cab, but I saw no problem with changing any other of the 50v fuses that were located in the cars, such as the door control fuses or even the 115v lighting fuses (if careful) and indeed I did on several occasions.

Many defects could be caused by a blown fuse and it was a process of elimination to decide if it was a fuse and if so, what one. With minor exceptions, the MG circuit would apply to all the Driving Motor cars on a 59 stock, the one at each end and the two in the middle. A blown fuse may give different symptoms depending on where it has blown and indeed may not even be noticed until the crew changes ends or have no affect at all in the middle.

The first indication that the 30A no.1 fuse had blown at the driver's end would be an audible warning because the feed to the EP brake would be lost. If the driver was motoring, he might notice the train being a bit sluggish as the control (motor operation) was lost. One way to prove if the fuse is OK would be to try the window wiper. Of course, the control key not being fully / the control barrel not fully turned would give exactly the same symptoms and so one of the first checks would be to ensure that the control key is fully in, especially if the driver had just opened up the train. Of course, an audible warning could also be due to a problem on the EP brake circuit and so there would also be various checks for that. It is being able to identify what a possible cause could be, depending on the symptoms, and then taking it from there which is the important thing.

A blown 30A no.1 fuse was what all drivers dreaded. There would be no control from the front of the train and no EP brake. The Guard would have to drive the train from the rear at caution speed, with the driver braking the train, using the Westinghouse brake at the front. The driver always did the braking, whether he was at the front or back of the train.


The MG takes 630v DC from the current rails and converts it to 115v AC for the fluorescent lights and 50v DC for the rest of the circuits. It also charges up the batteries, which are protected by a 70A fuse. A diode is provided in order to prevent current flowing back from the battery to the MG. During stock training on a 38 stock when all the shoes were paddled and lifted on the leading motor car, the Trainmen's Inspector (and us) was surprised to find the MG still running, albeit rather slowly. When the train was later checked by depot staff, it was found that the diode had short-circuited and the battery had in fact turned the generator part of the MG into a motor!

The gassing switch is used by the depot when they want to gas (or charge) the batteries quickly or give them a boost. Opening the gassing switch isolates all the 50v circuits and allows the full current to go from the MG to the battery. When the MG is not running, such as when the car is not on current, the battery supplies all the 50v circuits via the battery fuse. A blown battery fuse would normally have no effect on the train. However it was easy to tell if the battery fuse had blown on the front car because there would be an audible warning when going over long rail gaps as the EP brake lost its 50v feed. The solution as taught? "Do not stop on long rail gaps!". If the front car did stop on a long rail gap and became gapped, apart from losing the EP brake, the driver would have no control - the train couldn't motor. Unless the train could roll forward back onto current, the only solution was for the Guard to drive the train in reverse from the back cab until the front car was on current again. One way that I used to test if I suspected the battery fuse had blown was to stop the train just before a long rail gap on a downward slope. SB south of Camden Town going to Euston City was a favourite place. Stop the train, then let it roll forward. If there was an audible warning that lasted until the clunk of the shoes going back on the current rails, then the battery fuse had blown!

[Nortube]

The Compressor circuit - diagram at the end of this post
The compressor supplies the main line air that is needed for the pneumatic operation of the train

During the Guard's train equipment course, only the air side of the compressor was covered, not the control side. As a consequence, 'Compressors' was a new subject for the driver's course and was viewed with some apprehension. In fact, once you understand the basics, the compressor circuit is easy to follow.

On 38/59 stock, there were usually three compressors - two on the trailer car of the four car unit and one on the trailer of the three car unit. Originally the 38 stock had two compressors on each trailer, but one was later removed. The main line pipe runs the length of the train and all the compressors are connected to it. In theory, only one compressor is needed, but there would have to be a minimum of two in case one should fail. Also, the more compressors that are working, the faster the air is recharged as it is used. This is important as air is used for braking.


Each compressor has a compressor governor. This is basically a piston connected to the main line pipe. The piston rises and falls as the main line air pressure changes. There are contacts on the piston that make or break a circuit. When the main line is fully charged, the contacts are open, as the main line pressure falls, the contacts close.

From a driver's point of view, there are two main wires in the compressor circuit, the UNIT wire and the SYNCHRONISING wire.
50v DC comes from the MG or battery, through the 30A no.2 fuse and then through the 10A compressor fuse to the compressor button. A button is just a form of switch that was in common use at the time for all of the controls in the cab. There are two buttons - OFF and ON which control a rocker switch. Pressing the off button open the switch contacts, pressing the on button closes the contacts. These button switches were often very stiff and a job to push by hand, especially those that were rarely used. The usual way of operating them was to bash them in with the end of the reverser key! When describing the operation of a button switch, 'in' means on and 'out' means off .

50v goes from the compressor button to the unit wire and then to the Compressor Governor Cut-Out Switch. The arrangement is the same at both ends of the unit. The unit wire joins the two ComGCOS on the unit.

The ComGCOS is a double-blade knife switch and isolates the compressor governor it is associated with. Normally closed, when open it takes the 50v away from the governor contacts. This can be used if the  contacts stick in, meaning the compressor runs continuously, or for fault finding during a defect.

From the governor, 50v goes to the synchronising wire. The synchronising wire joins all the compressors on the train and makes sure that all compressors run when the contacts in any governor are closed. Synchronising the compressors in this way makes sure that all compressors get the same wear and tear. The synchronising wire goes through the Fault Isolating Switch in the cab, allowing the synchronising wire to be split into two for isolation in the event of a fault.

50v goes from the synchronising wire to the Compressor Cut-Out Switch, a single-blade knife switch situated next to the ComGCOS and then to the compressor coil. When energised, the compressor coil will hold the compressor contactor in and allow 630v DC traction current to the compressor. The compressor cut-out switch allows the compressor to be isolated if required

As can be seen from the diagram, only one compressor button needs to be in on the train for all the compressors to work. Normally the compressor button would be in at both end cabs and out in the middle. The only reason for the buttons being out in the middle is to make it easier when fault finding.

A brief summary of the 50v flow:
From the compressor button to the unit wire on that unit, through a compressor governor, to the synchronising wire and to all the compressor coils on the train. And that's it!


Defects on the compressor circuit
Various defects can occur and it is up to the driver, through a process of elimination, to identify what the defect is and carry out the necessary procedures in order to keep the train running.
A blown 30A no.2 fuse or 10A compressor fuse will mean that the unit wire on that unit has no 50v. The compressor fuse can be changed. If that doesn't have any effect or the 30A no.2 fuse has blown, it's no problem. The Guard will just make sure the compressor button is in in the rear cab.

A compressor contactor stuck in will cause all the compressors to run and thus main line air (normally 85psi) and train line air (65psi, fed from the main line air pipe) will overcharge. As long as the compressor buttons are cut out in the middle, all the driver has to do is cut out the button in his cab and this will prevent 50v going to the unit wire on the front unit. If the defective governor is on the rear unit, then the Guard will cut out the button in the rear cab. All the compressors can run as normal as their coils will still be fed via the governor(s) on the good unit.

A compressor contactor stuck in on a compressor means that just that compressor will run continuously. No great problem. The driver / Guard will keep a lookout for any signs of overheating.

[Ben]

On 38/59 stock, there were usually three compressors - two on the trailer car of the four car unit and one on the trailer of the three car unit. Originally the 38 stock had two compressors on each trailer, but one was later removed

Its interesting you say that as Graeme Bruce in 'Tube Trains under London' remarks that the 38ts had one compressor in each T and NDM (though werent some on the Northern line pre coupling abandonment equipped with two compressors on the three car unit?), whereas the 59ts had two per trailer regardless of unit length.

When did the 38ts NDMs have their compressors removed; was there some kind of programme to change the provision and standardise? Did the Acton Works strike have an effect on this all aswell?

[Nortube]

I'm certain that the 2nd compressor on the three car unit was removed during the strike due to shortages, although I'm not sure of the date.

I'll need to look up my 38 stock notes to confirm the 38 stock arrangements as it was a long while ago since I worked on them and my memory may be failing. I thought the 38 stock had both compressors on the trailer car, like the 59 stock, although I may be wrong. I'm certain that the three car units would have had two compressors on the trailer car in case of failure when running as a three car unit. If they were designed like that from the start, then it would make sense for the same arrangement to be made on both trailer cars. If the second compressor on the three car unit was fitted at a later date, then that's a different matter.

Ever since I can remember, the 59 stock on the Northern line have only had one compressor on the 3-car unit, although the control equipment for both compressors was still there. I suspect that the second compressor was either removed when the stock was transferred to the Northern line to replace the 38 stock, or they were removed at some point before that when they were on the Piccadilly line.

[Ben]

Thanks for that. Had a quick read, the 38ts seems to have had a second compressor fitted in the three car trailer as a result of the 1949ts programme, and had a 'C' stencilled below the car number.

What form did the diode take on the 38ts?

Where any details considered for the speculative integration of the 38ts and 59ts families, or was the scheme rejected too early on in planning? Seems very difficult to get any info out there on it.

About the lighting, when flourescent lights were introduced, why was 115v chosen instead of 240v? Also, did the lighting fuse ratings differ on the 38ts and 59ts?

All great information to read, thank you for sharing

[Nortube]

A quick reply until I get my notes.

I think that instructions, or whatever, came out at some point stating that a train in service should always have two compressors. It's possible that this was tied in with the 1949 programme. I'm afraid I don't know that much about specific details of the 38 stock equipment or the thoughts behind the different stock and there may be others on here that have the answers to what you are looking for.
I'm not sure what sort of diode was used. The standard diode symbol was shown, but I'm not sure if solid state diodes as such were around at the time, although it would have something solid rather than a valve or whatever.

I was told why 115v was used, but I forget why. Railtechnician may have answer to the significance of 115v. To the best of my knowledge, this was the first time that AC was used on Underground stock. It's possible that a higher voltage may have meant larger equipment. 115v would have been half the 230v which I think may have been the more common mains voltage at the time although, again, that may have no significance.
It's even possible that the AC may have originated from the 50v DC and changed via a rotary converter or something. I think the term Motor Alternator only began to be used on the 1962 stock diagrams and they were still called Motor Generators on the 1959 diagrams. The 1962 stock, although very similar to 1959 stock, and an almost identical circuit, did see some improvements and it's possible that they had a different style of MG/MA, hence the change of name. It's a similar thing that happened to the 1996/1995 stock. The 1995 stock, being later, had some improvements on the earlier 1996 stock.

One thing it did mean though was that the tubes rarely got stolen! Not sure if there was any difference in fuse ratings, I'll check them out.

[Nortube]

One thing I forgot to mention about these diagrams is that they are not necessarily complete. Guards and drivers were taught the everything they needed to know, but some irrelevant (to the crew) equivalent was sometimes omitted for clarity. Over the years, sometimes these things were were shown on the hand-outs, sometimes they weren't An example of this is that on the compressor circuit, there was also a fuse to protect the compressor coil and a fuse on the 630v side to protect the contactor. There may be other items, such as resistances that are not shown. Leaving these things out gave a clearer diagram and meant that there was less to confuse. Sometimes, various equipment may be grouped together and given a name, rather than show all the individual components.

With compressors, a driver couldn't change the compressor coil fuse or the compressor contactor fuse so leaving it off the diagram didn't matter. As far as the driver was concerned, if just one compressor didn't work, it was dud and that was it. It was different for the auxiliary, battery fuses etc. Although the driver couldn't change these on the early stock (some were later made accessible on later stock) they were shown on the diagrams because of the effect they had on the different parts of the MG circuit if they blew.

[Nortube]

I've had a quick look an managed to find some 38 stock hand-outs, but not the 38 stock MG diagram or my original Guard and Motoman's train equipment course notebooks. I did have a good clear out the other month and got rid of a lot of paperwork, but I still have plenty around and I think I still have them somewhere, although it may take a while to find.

You were correct about one of the four-car unit compressors being on the NDM. The compressor on the trailer was fed from the adjacent car (the 10,000 car). The compressor on the NDM was fed from the shoes on that car. On 59 stock, the feed to the second compressor was taken from the other DM car and taken through the NDM.

The hand-out I'm looking at was issued in 1986 when they reintroduced five 38 stock back on the Northern line (I thought it was six but one never ran). The train is shown with the two units coupled up with the A end at the end of the three-car unit and the D end at the end of the four-car unit. I'm certain that when they were on the Northern line the A was at the end of the four-car unit and the D was at the end of the three-car unit. A train was the correct way round if the A end was facing north. It's possible that the arrangements were different on the Bakerloo line where the five trains came from.

Diode
The 38 stock didn’t have a diode (I should have remembered that!) , they had a battery contactor. The 50v output from the MG also energised the battery contactor coil and closed the contactor, allowing the 50v to flow to the battery charger and all the 50v circuits. When the MG stopped running and the battery took over, the coil would de-energise and the contactor open, thus preventing 50v from the battery going back to the MG. In fact there were two sects of contacts on the contactor, the other was for the MG indicator light - the little over bright pygmy bulb that lit up when the MGs were running. This bulb was replaced by a much dimmer bulb and a metal flag that made an an annoying loud clunk as is dropped in and out when the car went over long rail gaps.
A stuck closed battery contactor was the reason that I mentioned earlier for the MG turning even though there was no traction current available.
Battery contactors were originally fitted on 59 stock, but later replaced with the more reliable solid state diode.

MG / MA
Looking at the 1962 stock MA diagram, the MA is shown as a Motor Alternator, with the alternator providing 230v AC. This was transformed and rectified to 50v DC. A centre tapping was taken from the 230v transformer to supply 115v AC to the fluorescent lights. Similar arrangements were used on later stock.

The MG on 59 stock was a combined Motor Generator/Alternator which provided an output of 50v DC and 115v AC. It would appear that the generator and alternator were both rotary equipment turned by the motor, rather than the later arrangement for 62 stock where the motor turned an alternator only. Presumably this was why they were still called MGs on the 59 stock.

[Nortube]

I've had another look and have now found my Motormans train equipment course notebook which contains my drawings and scribbles of thirty seven years ago!

Unfortunately, it doesn't show the lighting fuses at all, just the 50v feed going through contactors to a group of main lights and a group of emergency lights. The drawing in my book was copied from the drawing that the instructor drew on the blackboard, and in turn I expect that he drew it from the 38 stock hand-out. Therefore, even if I find the hand-out, it's not likely to show the details.

One thing I suspected, but didn't comment on until I confirmed it, was that the single compressor on the three-car unit was fed from the 10,xxx car, like on the four-car unit. The train formation was also as I suspected - 4-car unit on the front, with the A end (10,000 ) at the north end, with the three car unit and 11,xxx car at the rear, with the D end at the south. Therefore, the 10,XXX DM on the three-car unit was in the middle and not at the end. This gave rise to problems when trains were stabled wrong way round in the sheds at Morden depot. When the train was pulled up with the leading car (11,xxx) "on juice", it meant that there would be no compressors on the front unit.

This wasn't normally much of a problem because the jumper leads would be put in the back car and in at least one of the middle cars to keep the train charged up. Problems could arise when the train was called into service. Once the brake test was completed, normal practice was for the Guard to take any leads out of the middle of the train, then the driver would instruct the Guard to take the leads out of his car when the train was called up.

One problem was if, when the train was called up to depart, the driver or an over eager trainee dropped the handle when preparing to depart, or at any time until the next DM was on juice. Depending on how quick the deadman was reset, there might not be sufficient main line air for the control governor to cut in and thus the train couldn't move until the leads were put back in and main line fully recharged.  This could take as much as five minutes. As a shunter, this wasn't what you wanted when you had trains going into service every three minutes, especially when there was no radio contact in those days and you had no idea what the delay was. Once a train had been called up, to avoid the risk of a collision, another train couldn't be called up on the same side until you had confirmation from the delayed driver that they weren't going to move. One way or another, this could end up with a long delay.

[Ben]

Fantastic, many thanks, some very interesting stuff to plug the gaps from books.

Out of interest why was the 6th train never reinstated, was it rehabilitated like the others, or just made workable and transfered as a spare?

At the begining the 38ts seems to have run in almost every permutation possible, including DM-NDM-DM+DM-T-DM on the Bakerloo. And all the block trains on the Northern related to the 9car project.

Did the 56ts have anything in common with the 38/49ts that it didn't with the 59ts run?

Thanks for your replies.

[Nortube]

I seem to recall that the term used for the sixth train was "knackered"! Possibly used for spares.

I can't remember what the difference was between the 56 and the 59 stock. If I come across anything I'll post it. I vaguely recall there were some cosmetic differences between them, but I'm not sure what any mechanical differences were. It's a long while ago since I was one one, but an easy way to tell if you saw one approaching was that the headlights were the old marker light type layout whereas the 59 stock were the two bulbs.

[Nortube]

The EP brake
The EP brake is the main brake used on 1938 -1962 stock trains

see the Off and Release post for the first diagram

Description
The EP brake is Electro-Pneumatic. Electricity is used to control the air flow to the brake cylinders. The EP brake is fast acting, with the same amount of braking on all cars at the same time, but is not fail safe. Any loss of the 50v supply and the brakes will release / cannot apply. Because of this, the fail-safe Westinghouse brake is used as a back up. That works purely by air.

The EP brake uses air from the 85psi main line pipe. Here we will look at the electrical circuit that controls the flow of air. As with other train equipment diagrams, these only show the basics. The description will be a detailed one, spread over several posts with several diagrams. This is the longest post.
If you want to follow the description, it's best to print off the diagrams. Open the attachments and print them or Save the attachments and then print them. This first post gives a description of the components. In this, and the brake position descriptions, it is assumed that the cab is opened up and everything is working correctly.


The main components are:
Magnet valves: - three per car. These control the flow of air in and out of the brake cylinders
Retarders:  - there are two retarders on each driving motor car (located in the cab on 38 stock). They apply additional control to the brake application in order to prevent wheel lock which would reduce the braking efficiency. Only the retarders in the cab that the train is being driven from will be operational.
Fingers and slider: - make or break contact according to the position of the brake handle
Audible warning magnet valve:  -gives the driver a warning if the 50v EP brake supply fails

50v comes from the battery, through the 30A no.1 fuse, the control key switch, 10A EP brake fuse, EPBrake Isolating Switch button and the Driver's Brake Valve Isolating Cock. From the EP brake point of view, the DBVIC can be thought of as just another switch in the 50v supply. When a cab is "opened up", the control key is inserted and the control switch is turned on and the DBVIC is opened up using the driver's reverser key. The 50v supply is now complete. When the cab is shut down, the 50v supply to the EP brake circuit is lost.

The first diagram shows the brake handle in the Off and Release position. This means what it says. The brakes are not applying and are released. This is the normal position for the brake handle to be when the train is motoring or coasting. The train could be motoring or coasting. Let's have a look at what makes up the circuit.:


The components of the EP brake circuit
Application magnet valve - normally closed. 50v is required to open the valve.
This is the valve that lets air into the brake pipe which goes to the brake cylinders on that car.  Air at 85psi comes from the main line pipe to the valve. An EPBrake Isolating Cock is provided to isolate the air from the valve in the event of a defect. This valve is only open when it is necessary to put air into the brake pipe. Loss of the 50v supply will close the valve, preventing any further air going into the brake cylinders. It is controlled by number 1 retarder. As the brake handle is in off, the valve is closed.

Holding magnet valve - normally open. 50v is required to close the valve.
This valve holds the air in the brake cylinders. Loss of the 50v supply will open the valve, allowing any air in the brake cylinders to escape to atmosphere. As the brake handle is in off, the valve is open.

Blowdown magnet valve - set at 28-31psi. Normally closed. Loss of the 50v supply will open the valve and air in excess of 28-31psi will escape to atmosphere. Maximum brake pressure when open is 28-31psi. It is controlled by the number 2 retarder. As the brake handle is in off, the valve is closed.

Interlocks are the connection on the different wires and they can be thought of as switches - either open (breaking the circuit) or closed (completing the circuit). The opening and closing of the interlocks can be controlled in different ways - relay, solenoid, mechanical switch etc. The interlocks shown in the diagrams are shown in their very basic form.

Retarders. These are glass tubes filled with mercury. The mercury is conductive and 50v passes through it to make or break contact as required. A retarder can be thought of as a switch.
Retarder no. 1 controls the application magnet valve via the application relay.
Retarder no.2 controls the blowdown magnet valve via the blowdown relay.

Application Wire, Blowdown Wire and Holding Wire.
These wires go to the magnet valves on each car throughout the train and to each cab, although they will only be controlled from the opened up cab.

Interlock wire
Fed from the Blowdown wire at the rear of the train, the interlock wire goes from the rear to the front of the train. Each magnet valve on each car has an interlock that makes contact with the interlock wire. It can be thought of as a magnet valve proving wire, proving that all the magnet valves are working correctly.

DBVIC proving wire
Fed from the Blowdown wire at the rear of the train, this runs through the rear and middle DBVICs to prove that they are closed.  Although not shown on the diagram, the DBVIC proving wire also goes through the auto coupler disconnecting unit.

Audible Warning magnet valve - normally closed. 50v is required to close the valve.
This valve connects to the main line pipe and when open allows a small amount of air to atmosphere to give a loud noise. This acts as a warning.
Other than in the Off and Release position, the valve will open if one or more of the interlocks are not closed on the Interlock wire or the rear or one of the middle DBVICs are open. The valve will open if the 50v supply to the EP circuit is lost, such as when the 30A no.1 fuse or 10A EP fuse blows, control key not inserted or the EP brake is switched off in the front cab.
The air supply passes through the DBVIC to the valve. When the DBVIC is closed, although the valve is open, there is no air supply to the valve and thus no noise. There is also an Audible Warning Isolating Cock located within the DBVIC that can be opened. This will block the air from escaping from the valve. This is only used when there is a defect and the EP brake has been cut out (the driver will be driving at reduced speed and braking using Westinghouse).

Fingers
The fingers are a set of metal contacts that are connected to the different wires as shown in the diagram.
The brake handle is connected to a self-lapping mechanism (not covered here) and the slider is part of this. Basically, the slider is just a sliding contact which moves along the fingers, making and breaking contact between them. The self-lapping mechanism regulates the amount of air in the brake cylinders according to the position of the brake handle in the application position.

Triple valve
The triple valve is part of the Westinghouse brake system (not covered here). When using the Westinghouse brake, train line air, not main line, is put into the brake cylinders under the control of the triple valve. When the brakes are released, air from the brake cylinders goes through the brake pipe, through the TBVIC and then through the open holding magnet valve to atmosphere.
When the EP brake is cut out, the holding valve is de-energised open. By controlling the air flow, the triple valve ensures that no air escapes from to atmosphere from the brake cylinders when the Westinghouse brake is applied.  A faulty triple valve can cause the EP brake to hang on on that car if it is preventing air from the brake pipe going to the holding magnet valve when the EP brake is released.

There are five positions on the brake handle:
1)  Off and Release
2)  Application
3)  Lap
4)  Service application (Westinghouse)
5)  Emergency

In the position descriptions in the following posts, description of an application, blowdown or holding magnet valve operation refers to the operation of that valve on all of the cars on the train at the same time. All the same type of valve are connected in parallel throughout the train.
 

[Nortube]

The EP brake circuit (diagram at the end of this post)

Off and Release
In the following description, it is assumed that the cab is opened up and everything is working correctly. The train could be motoring or coasting.

50v goes to the Supply finger and to the mercury in retarder 2. The mercury is not touching the blowdown relay contact in the retarder, and so the interlock on the blowdown wire is closed, allowing 50v to go to the Blowdown Wire.
The blowdown magnet valve will be closed and its interlock making contact with the Interlock Wire.

50v goes to the Interlock Wire but, because the holding magnet valve is open, it cannot go any further.

50v goes to the DBVIC proving wire, through the closed rear and middle cab DBVICs, though the closed audible warning contact and to the audible warning magnet valve relay which energises and closes the audible warning magnet valve.

The audible warning contact only makes in the no. 1 position (Off and Release). It does this because in Off and Release, the slider is only making contact with the audible warning finger and thus there is no 50v supply from the supply finger to the audible warning finger.

[Nortube]

The EP brake circuit (diagram at the end of this post)

Application - stage 1
The brake handle is in a braking position
The slider connects the Supply, Holding and Application fingers together

50v goes to the Supply finger and to the mercury in retarder 2. The mercury is not touching the blowdown relay contact in the retarder, and so the blowdown relay coil is de-energised the interlock on the blowdown wire is closed, allowing 50v to go to the Blowdown Wire.
The blowdown magnet valve will be closed and its interlock making contact on the Interlock Wire.

50v goes to the Holding Wire, energising and closing the Holding magnet valve. No air can escape from the brake cylinders. The holding magnet valve interlock will also be closed.

50v goes to retarder 1, through the mercury and energises the application relay coil. This closes the interlock and 50v goes to the Application Wire, energising and opening the application magnet valve. Main line air can now go to the brake cylinders. The application magnet valve interlock will also be closed.

All the interlocks on the interlock wire are now closed and 50v flows along the Blowdown wire, then the Interlock wire, energising and closing the audible warning magnet valve. The audible warning contact is open because it is only closed in Off and Release.

If the brake handle is moved to the end of the Application range - Full EP, the self-lapper is by-passed and main line air will be continually fed into the brake pipe


Application - stage 2
The brake handle is in a braking position
The slider connects the Supply, Holding and Application fingers together

The braking momentum of the train is causing the mercury to move in the retarders.

In number 1 retarder, the mercury moves away from the application relay contact, de-energising the application relay coil and the application relay interlock drops out. There is no longer 50v on the Application Wire and the application magnet valves become de-energised and close, thus preventing any more air entering the brake cylinders.

At the same time, the mercury in number 2 retarder makes contact and completes the circuit sending 50v to the audible warning relay to keep it energised as there will no longer be a feed to it via the Interlocking Wire because the application magnet valve contacts will be open.


Application - stage 3
The brake handle is in a braking position
The slider connects the Supply, Holding and Application fingers together

The continuing braking momentum of the train is causing the mercury to move further in the retarders.

In number 1 retarder, the mercury just moves further away from the contact and has no further effect

In number 2 retarder, the mercury is now touching the blowdown relay contact and 50v flows to the blowdown relay coil, energising it and opening the blowdown relay interlock.
50v will be lost to the Blowdown Wire. The blowdown magnet valve will be de-energised and open, allowing all air in excess of 28-31lb in the brake cylinders to go to atmosphere. Braking will now be lighter and the momentum reduced.

As a consequence, the mercury will return to its normal position in the retarders.

If the brake handle is still in the Application position, the blowdown magnet valve will now be energised closed to allow the maximum brake pressure, and the application magnet valve will now open to allow more air into the brake cylinders. All the interlocks on the Interlock Wire will be closed and the 50v will flow along it to keep the audible warning magnet valve energised.


If the train braking momentum builds up again, the whole process may repeat itself. The actual process is quite quick and may be repeated every few seconds. Although rarely heard these days with the newer trains and different types of braking, the sound of the blowdown valves continually venting used to be quite common in some places.

When braking, a train may never get to stage 2 or 3, depending on various things such as how heavy the brake application is, how steep the gradient or even how full the train is.

Stages 2 and 3 are used to help prevent the risk of wheels temporarily locking. Locked wheels reduce the effectiveness of the brake (ask any driver who has approached a fast station in the rain only to hear it go deadly quiet as the wheels locked and the train sails on!) and can also lead to flatted wheels. Flats are where, when the wheels lock and  a tiny amount of the wheel's tire may be ground flat. The noise flats make are totally out of proportion to the actual size of the flat. The way that the braking systems work on the newer stock mean that flats are very rare these days.


Application stage 1                      Application stage 2                     Application stage 3