How to Lock-Up Brakes?

 
  PaulM Station Staff

Forgive the newbie question, but how is it possible to 'lock-up' (ie overcharge) carriage air brakes? I've heard stories of exasperated freight drivers having to walk the entire length of their train to release air from the brake cylinders of every carriage.

From what I understand of air brakes - admittedly not a whole lot - the brake pipe won't go higher than 500 kPa. I know that with the No 4 W valve, which runs air straight from the main reservoir to the locomotive brakes, it's possible to end up with over 500 kPa in the locomotive brake cylinders. But how is this possible with brake pipe air running via an equalising reservoir? What is the unfortunate combination of 26L applications that could give you overcharged brake cylinders?

Many thanks for any information.

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  gordon_s1942 Chief Commissioner

Location: Central Tablelands of NSW
It was common practise when you were trying to move a vehicle by manpower (muscles or Pinchbar) to pull the release to expel any air in the system no matter how long the vehicle had been off the air.
You wound out the handbrakes and kicked every set of shoes you could reach to reduce any friction between the wheel and the shoe.
Even when using a locomotive you did this for 'loose' shunting'.
There is nothing worse than after giving something a shove and having it stop short of where you want it to go because of dragging brakes so you 'bled' first to make sure you had an empty system.
You have to remember the gear used on the braking system was fairly rudimentary and had changed little since brakes began to be used.
Much of it relied on Gravity to release and it didnt take much for the mechanism to jam up.

Another problem is that scale can build up on a wheel face if the brakes arent fully released fully.
The other is a 'Flat spot', both of which can cause a wheel to derail.

Air pressure for a passenger was 80lb per square inch , ie 7 X 80 = 560 Kpa.
Goods were 60 lb per square inch , ie 7 X 60 = 420 Kpa.

One problem was not the pressure but the volume as in the early days, the compressor's on a 46 class were so powerful that the engine could break away from its load and with the tap wide open, drive on without any effect on its brakes nor would the Driver see any indication on the 'Flow Meter' of this happening.
We wanted the Guard to pull the tail of a 4 car passenger set hauled by a 46 class to stop it but he shrugged his shoulders and yelled out that it would not stop the train.
  YM-Mundrabilla Minister for Railways

Location: Mundrabilla but I'd rather be in Narvik
It was common practise when you were trying to move a vehicle by manpower (muscles or Pinchbar) to pull the release to expel any air in the system no matter how long the vehicle had been off the air.
You wound out the handbrakes and kicked every set of shoes you could reach to reduce any friction between the wheel and the shoe.
Even when using a locomotive you did this for 'loose' shunting'.
There is nothing worse than after giving something a shove and having it stop short of where you want it to go because of dragging brakes so you 'bled' first to make sure you had an empty system.
You have to remember the gear used on the braking system was fairly rudimentary and had changed little since brakes began to be used.
Much of it relied on Gravity to release and it didnt take much for the mechanism to jam up.

Another problem is that scale can build up on a wheel face if the brakes arent fully released fully.
The other is a 'Flat spot', both of which can cause a wheel to derail.

Air pressure for a passenger was 80lb per square inch , ie 7 X 80 = 560 Kpa.
Goods were 60 lb per square inch , ie 7 X 60 = 420 Kpa.

One problem was not the pressure but the volume as in the early days, the compressor's on a 46 class were so powerful that the engine could break away from its load and with the tap wide open, drive on without any effect on its brakes nor would the Driver see any indication on the 'Flow Meter' of this happening.
We wanted the Guard to pull the tail of a 4 car passenger set hauled by a 46 class to stop it but he shrugged his shoulders and yelled out that it would not stop the train.
gordon_s1942
I don't think that this is what PaulM is asking about.
  KRviator Moderator

Location: Up the front
The simplest and easiest way to overcharge the train is with a loco fitted with a B7 brake valve and putting the handle in the release position and leaving it there, as you normally do on every other loco... Despite its' cunningly-devised name, such a position, while indeed releasing the brakes, does so by permitting air from the Main Resevoir to flow directly into the BP. This in turn raises the BP above the desired 500Kpa so when you move the handle to the running position, you now have a 200-odd-kpa reduction in BP pressure which reapplies the brakes. Cue walking the train.

Short of going to the release position again, there is now no way to get the brakes off from the loco. Furthermore, the MR is not regulated as rigidly as BP pressure, instead being governed over a range of 650-750Kpa, so you run the risk of uncommanded applications and releases if you were foolish enough to attempt to work the train in this manner.

Another easy way to have similar problems is to have a loco with a BP set-point slightly high, then detach it, or attach a new lead loco with its' BP set-point slightly low. When you open the BP between the locos, the pressure reduction can cause an application, even though the now cut-in loco's auto brake handle is released. IIRC, the solution to this occurrence was two full-service applications and releases, which would reduce & recharge the wagon aux reservoirs enough to respond appropriately to the new BP pressure. This can occur on loco's as well as wagons if you don't bail-off enough.
  PaulM Station Staff

Gordon, thanks for your interesting, in-depth reply. It sounds like you have a rather deep well of personal experience to draw from!

As KRviator mentioned, my question was following a slightly different track. Any current drivers out there care to venture an opinion?
  DRR_Fireman Deputy Commissioner

Location: -
Gordon, thanks for your interesting, in-depth reply. It sounds like you have a rather deep well of personal experience to draw from!

As KRviator mentioned, my question was following a slightly different track. Any current drivers out there care to venture an opinion?
PaulM
KRviator as pretty much answered the question. As far as I know he is currently a driver.
  fzr560 Chief Train Controller

Gordon, thanks for your interesting, in-depth reply. It sounds like you have a rather deep well of personal experience to draw from!

As KRviator mentioned, my question was following a slightly different track. Any current drivers out there care to venture an opinion?
KRviator as pretty much answered the question. As far as I know he is currently a driver.
DRR_Fireman
To add to what has been posted(and not contradict), AFAIK, by far the most common cases of overcharging the BP occurred with A7/B7 brakevalve to the extent that some brake valves were modified to prevent the use of the quick release position. As KR described, unwanted applications are still possible with later brakevalves, but it's not a design "feature".
  YM-Mundrabilla Minister for Railways

Location: Mundrabilla but I'd rather be in Narvik
Gordon, thanks for your interesting, in-depth reply. It sounds like you have a rather deep well of personal experience to draw from!

As KRviator mentioned, my question was following a slightly different track. Any current drivers out there care to venture an opinion?
KRviator as pretty much answered the question. As far as I know he is currently a driver.
To add to what has been posted(and not contradict), AFAIK, by far the most common cases of overcharging the BP occurred with A7/B7 brakevalve to the extent that some brake valves were modified to prevent the use of the quick release position. As KR described, unwanted applications are still possible with later brakevalves, but it's not a design "feature".
fzr560
This perhaps tends to confirm something that I thought was the case, but was not sufficiently confident to say. My understanding was that the VR blanked off the release position on some A7 brake valves. This was prior to through working to SA IIRC when the release position was reinstated IIRC.
Open to correction, however.
  KRviator Moderator

Location: Up the front
There was always talk of PN wanting to blank off the release position on the B7's fitted to their 48's, but in my time with them, it wasn't done on any loco's I worked - even though we were instructed not to use it for fear of overcharging the BP.
  YM-Mundrabilla Minister for Railways

Location: Mundrabilla but I'd rather be in Narvik
There was always talk of PN wanting to blank off the release position on the B7's fitted to their 48's, but in my time with them, it wasn't done on any loco's I worked - even though we were instructed not to use it for fear of overcharging the BP.
KRviator
Thanks KRviator. More or less confirms what I had in the back of my mind somewhere.
(See, I didn't make it up after all Smile )
  PaulM Station Staff

Gordon, thanks for your interesting, in-depth reply. It sounds like you have a rather deep well of personal experience to draw from!

As KRviator mentioned, my question was following a slightly different track. Any current drivers out there care to venture an opinion?
KRviator as pretty much answered the question. As far as I know he is currently a driver.
DRR_Fireman
Indeed he did!

Apologies if my post was worded ambiguously. I was referring the earlier post by Gordon, not the one by KRviator.
  a6et Minister for Railways

There was always talk of PN wanting to blank off the release position on the B7's fitted to their 48's, but in my time with them, it wasn't done on any loco's I worked - even though we were instructed not to use it for fear of overcharging the BP.
KRviator
KV, sticking brakes with the older BV's was more often caused with vehicles that had old triple valves, and grade control valves that tended to get clogged up with road grime including brake dust, especially when older trains had to operate in HP position for long heavy grade descents.  Even further back was the requirement to set hand brakes as well, again creating the continual brake dust problem.  Later Relay and choke valve equipped wagons did not seem to have the same problem, 26L and later BV's were better with those types of wagons as they did not have the kick ability.

We were told to have the rotary valve setting for goods services at 70psi 60 for Passenger stock. Descending the blue mountains, and Illawarra Mountain you put the BP up to 90psi, as you came to the bottom of the grades, you began reducing the rotary valve back to the normal setting of 70, at the last such reduction you gave it a very heavy reduction once you came to a stand, and then released the brakes. Off the escarpment you generally didn't worry if you were only going into Unanderra sidings, but if heading to PTK you would.

Off the mountains, the fireman and guard met half way at either Springwood or Valley, putting the GCV's back to IP or exh depending on the driver, barring in mind that with regen on the 46 would control the trains exceptionally well for the rest of the journey, also on the short north to and from Gosford on the 1:40's so no need of the GCV's except in IP.

When I worked with drivers in steam days, and prior to going into the A/Driver school, the big thing in the teaching and use of the old BV's was that when you released the brakes, you held the handle over in the full release position for 1 second for every vehicle on the train, be that #4, A6ET, 6ET, A7EL, B7El and  7EL, bring the handle back to Release and Running (R&R) for 2 seconds and give a 1 second kick to full release back to R&R.

The idea, and it mostly worked was that you sent an extra amount of air through the Brake pipe, above the rotaryvalve/auxillaries setting in basically a rushed setting to push any dirt out of the triples etc, likewise the secondary short kick.   That would normally work without a lot of problems, except as I said with some old vehicles fitted with Triples, and or GCV's which were put into positions other than Exhaust (normal release), most sticking brakes occured with the triples in IP, retarded release, owing to the dirt build up. If the sticking continued we cut them out out tied a defect card on the Triple valve handle.

Over the years I had relatively few sticking brake encounters, as what I found was that in the main, most trains did not need the GCV's set in other than IP, in fact many drivers even when working high wheelers would ask the examiners to not put them in, or at crew change points if the train had an examiner check at the changeover point, would ask for them to be taken out. That was especially the case on the Short North and Short South, never had them in out of WCK except heading to BMD, or down the Moonbis, and Illawarra, except the mountain and heavy trains to Enfield with 48cl working them.

In my later years, I noticed some new men, not using the old methods, and simply putting the handles into R&R on all old equipped loco's.

In response to what Gordon had to say, many shunters when a train came in and had to be shunted, would walk the train and tie a minimum number of hand brakes on in order to hold the train, and walk back and place a piece of small ballast/stick or whatever was found on the ground into the release handles throat, in order to hold the release port open without them standing and holding it open.  Problems occured though, if the fitted piece broke and some was stuck in the ports throat, which could cause faulty brakes on that vehicle, unless it was blown out when the train was made up and the air went through the train.

I watch many of the modern trains go through Wyong, and I find that there are as many vehicles with flat wheels these days if not more than in my times, that's even on EOT pulse (or whatever its called) braking, another topic I guess, but often related to the operation of the air.

PS, as an edit in.  The old #4 BV, used on most steam loco's including the 57cl and 36cl but with an engine only brake plus #4 for train working, the regulations provided for the handle to be place in the full release position when descending the two main mountains. The compressors had a governor that was set to a constant 100psi for the main reservoir, with this method you operated at the full MR air charge going down the 30's and when at the bottom you put the handle back to R&R at the rotary valve setting.  This meant that in the standing they had to make 3 very heavy reductions and the normal release operations to get the brakes release without the danger of sticking brakes.  Also, in the steam days, with those loco's (not the 58's or engines fitted with A6ET BV's) part of the fireman and guards job was as they released the hand brakes they also had to drain any air by holding the release valve open.
  a6et Minister for Railways

There was always talk of PN wanting to blank off the release position on the B7's fitted to their 48's, but in my time with them, it wasn't done on any loco's I worked - even though we were instructed not to use it for fear of overcharging the BP.
KRviator
KV, I would imagine that it was owing to the use of their 830's here in NSW to keep them compatible with air regulations. Some of them also were fitted with A7 BV's like our Mk 1 48's.

Even the 600's had to be remodded for use here, not much but little things.

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