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| Some technical questions on Brakes; Exmoor engines, continuous air brakes, | |
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| Tweet Topic Started: 29 Apr 2009, 09:23 PM (1,796 Views) | |
| Andrew | 29 Apr 2009, 09:23 PM Post #1 |
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CME, Stackton Tressel Light Railway.
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Hi guys, I’ve got a few technical questions that I would like to quiz some of the members of this forum with. Question one; I notice that on all Exmoor built engines and even on ‘Dougal’ that there is a pipe that seems to exit on each side on the loco under the back end of the tank. The pipe looks to be about 1” in dia, I’m struggling to work out its use. By best guess is that it’s part of a boiler blow down? The pipe is there on Dougal and hides behind the hole in the back lower tank plate. Question two; (This breaks down into lots of questions really) As answered on another thread, Dougal carries its own air compressor, both battery and axle driven. The air is undoubtedly for continuous air brakes. On the EVLR is this the standard single pipe air braking system? e.g. Charging the system from the engine (used to be ‘on the system I used’, 80-60 psi charges the system, 60 psi releases the brakes, 50-30 psi applies the brakes and 30-0 psi provides an emergency application) However, I have come across an extremely simple, pump air into the train pipe to apply the brakes. This is not correct continuous brakes (guarding against train splitting) but it does provide train braking. Assuming that a single pipe system is being employed, this assumes that each engine must carry its own compressor and air reservoir. Where do some locos have all this kit? Price William? I can see that some railways employ the twin pipe system (Longleat) which means that the compressor can be situated on the train. In fact this is exactly the method we used to operate air braked stock when we ran ‘Steam on the Met’. But this method of compressor on the train is impossible with a single pipe system. So where on earth does ‘Spirit of Adventure’ have a compressor and reservoir? The only available space as far as I can see, is in one of the coal bunkers? The problem I have is that I had very little to do with air braking on standard gauge, vacuum brakes is a different matter. I designed the vacuum brake system for 'Fire Fly'. I’ll leave these questions here for the time being, but rest assured that I’ve got many more…. |
| Andrew. | |
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| bvr379 | 30 Apr 2009, 03:35 PM Post #2 |
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On the Bure Valley Railway a single pipe system is used similar to the description above. Compressed air is produced on the locomotives using both a "Westinghouse" type steam pump and an axle driven compressor (except #1 - see below). On BVR#6 & #7 (2-6-2 Tender locos) the axle pump is driven off the rear tender wheels as is the battery charger and speed recorder - all located in a compartment at the rear of the tender. The tank locos, #1, #8 & #9 have similar arrangements except that #1 does not have an axle driven compressor. In addition, all locos have steam brakes & hand brakes. Locos #8 & #9 also have air brakes on their driving wheels, similar to coaches. Locos #6 & #7 have air brakes on their tender wheels, similar to coaches. A valve is currently being manufactured by the BVR so that the air brake system applies the steam brakes on locos #1, #6 & #7, as well as being able to apply the steam brake directly. There are restrictor valves on the air control systems on the locos so that if the Guard dumps the brakes, the locos cannot pump air into the train pipe faster than the Guard can dump the air. There also additional small 5L reservoirs on all locos, except #9, to speed up the air brake release. The main air reservoirs on the Tender locos are under the tender. The air reservoirs on the tank locos are: #1 under the coal bunk, beside cab footsteps; #8 between the tanks and the top of the boiler (a tube either side of the boiler) & #9 under coal bunker and between the main frames under the boiler (3 No. reservoirs in total.) All coaches have 10L reservoirs. |
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David Barnes Bure Valley Railway - The 15" gauge railway with powerful steam locomotives. Trains between Wroxham & Aylsham in Norfolk. Daily services between 24th March and 28th October 2018. Please look up the BVR website, for more details. | |
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| craiggluyas | 30 Apr 2009, 04:08 PM Post #3 |
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Question one; I notice that on all Exmoor built engines and even on ‘Dougal’ that there is a pipe that seems to exit on each side on the loco under the back end of the tank. The pipe looks to be about 1” in dia, I’m struggling to work out its use. By best guess is that it’s part of a boiler blow down? The pipe is there on Dougal and hides behind the hole in the back lower tank plate. Yes it is the Blowdown Question two; (This breaks down into lots of questions really) As answered on another thread, Dougal carries its own air compressor, both battery and axle driven. The air is undoubtedly for continuous air brakes. On the EVLR is this the standard single pipe air braking system? e.g. Charging the system from the engine (used to be ‘on the system I used’, 80-60 psi charges the system, 60 psi releases the brakes, 50-30 psi applies the brakes and 30-0 psi provides an emergency application) However, I have come across an extremely simple, pump air into the train pipe to apply the brakes. This is not correct continuous brakes (guarding against train splitting) but it does provide train braking. Assuming that a single pipe system is being employed, this assumes that each engine must carry its own compressor and air reservoir. Where do some locos have all this kit? Price William? EVLR runs a single pipe system using Triple Valves. Reduce the pipe pressure to below 40 PSI and the brakes apply. By 35 PSI the brakes are fully on. The use of triple valves is less common now as sources have dried up. Ratty, EVLR and BVR are the only ones, the other lines using another single pipe system which relies on a twin acting cylinder and balancing pressures on either side of the piston, one from a reservoir and the other from the train pipe. The compressors are located on the locos, Prince William has an axle driven one and a battery back up under the seat, as does John, Dougal & The switcher. St Egwin has a HUGE axle driven compressor. Straight air brakes are not an option any more. If there is a requirement for brakes greater than those on the loco only, it has to be fail safe. I can see that some railways employ the twin pipe system (Longleat) which means that the compressor can be situated on the train. In fact this is exactly the method we used to operate air braked stock when we ran ‘Steam on the Met’. Nope. The twin pipe system on Miniature railways is different to that on standard gauge. Std gauge use the supply line to charge the brake reservoirs to allow the brakes to come off faster. The system you have seen at longleat, is standard to Severn Lamb and Keef stock (& Scarborough) and uses HGV parts, simulating the loco as the tractor unit and the coaches as the trailers. Straight air brakes are used on the yellow line, allowing normal service braking. Raise the air pressure and the brakes come on. The heart of this system is the emergency relay valve, which works similar to a triple valve. The red line is pressurized to over 40 psi, this passes through the valve and into the tank. As long as this line stays above 40 psi the brakes are only operated from the yellow line. If the pressure drops below 40 PSI (eg because of a train split), the relay valve automatically directs the air from the reservoir into the brake cylinder, applying the brakes. The brakes cannot now be released without re-charging the line or venting the cylinder. If a spring brake chamber is used, the red line is simply directed into the spring chamber, the yellow line working the straight brake as before. My personal preference is to the 2 pipe system, as it can give greater control, and parts are more readily available & cheaper. However, that may be due to my HGV design background! The single pipe system is simpler between the coaches, but the component parts are more expensive. In theory you could supply the loco with air through the Red line, however if the pressure dropped below the magic 40 PSI during a small brake application, the lot would come on! But this method of compressor on the train is impossible with a single pipe system. So where on earth does ‘Spirit of Adventure’ have a compressor and reservoir? The only available space as far as I can see, is in one of the coal bunkers? Pretty sure its in the bunkers, athough there is room on exmoors between the frames, which is where St Christophers will go if it gets one! It spent some time at CCLR so perhaps someone from there can remember! The problem I have is that I had very little to do with air braking on standard gauge, vacuum brakes is a different matter. I designed the vacuum brake system for 'Fire Fly'. I’ll leave these questions here for the time being, but rest assured that I’ve got many more…. And We'll keep answering them!! Edited by craiggluyas, 30 Apr 2009, 04:10 PM.
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Craig Gluyas Talking to one's self is a sign of madness. I talk to my imaginary friend. | |
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| Andrew | 30 Apr 2009, 04:43 PM Post #4 |
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CME, Stackton Tressel Light Railway.
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Grateful thanks to both David and Craig.
I'm not at all surprised to find that this is now the case, but I have seen some pretty odd things in the past. With the exception of the Nene Valley Thomas the Tank Engine and a few odd turns at the Nene when 3822 was there, LT has been my only real experience of air brakes. The air brake system that I mentioned using on the 'Met' was not a true twin pipe system. It was an in house designed hybrid so that the vacuum braked engines could operate the train air brakes. The air supply being provided by either 'Sarah Siddons' or the 'Class 20'. As far as I can remember (it was ten years ago now) the whole worked as a single pipe system with a second pipe for the drivers brake valve air supply. We built a bloody great column for 4144 to go in the cab for a Westinghouse drivers brake valve which was conected to the train with 'miles' of flexible hosing. It seriously cut down the amount of space in an already cramped cab, plus the four crew. Me, my fireman, an LT Inspector and a very worried looking pilotman. These pilotmen were an interesting addition, insisted upon by the Union of all things!!! The point was they were just normally rostered 'Tin Worm' drivers that found themselves on the footplate with no prior warning or knowledge. All rather odd, for both them and us. The one thing that the LT staff kept banging on about all through our route training was not to keep making small air dumps to the train pipe without putting the handle back to the full release position and charging up the reservoirs. Apparently a previously driver had done this in much the same way as he would when using vacuum and when it came to the crunch he'd drained the reservoirs on the stock, with obvious results. This must be the case with all single pipe air brakes but if you're used to vacuum brakes it comes as a bit of a shock.... |
| Andrew. | |
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| Andrew | 30 Apr 2009, 05:16 PM Post #5 |
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CME, Stackton Tressel Light Railway.
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Is this compressor on the loco or tender, and does it not have a battery powered compressor too? If it does not, how does the system pressurize during prep? Also, is any of the stock fitted with compressors, axle driven or otherwise? |
| Andrew. | |
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| bvr379 | 30 Apr 2009, 05:17 PM Post #6 |
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Yes, Yes, Yes! It is all part of the training & testing of drivers and one of the reason why an "owners" driver normally goes with the owners loco when there are visits to other railways. One other point as Craig has mentioned HGV components. - Do not use those long curly HGV airlines. If trains divide they can get sealed by vehicle wheels and then do not release air! |
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David Barnes Bure Valley Railway - The 15" gauge railway with powerful steam locomotives. Trains between Wroxham & Aylsham in Norfolk. Daily services between 24th March and 28th October 2018. Please look up the BVR website, for more details. | |
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| craiggluyas | 30 Apr 2009, 05:27 PM Post #7 |
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In the tender, under the seat. No battery compressor, unlike the others. Charging during "prep" is from the external compressor used to steam up, which is pretty standard for axle driven stuff, via an air line. Charge the tanks up to 100psi or so, and it is quite happy all day. The compressor is quite a large commercially available one from Machine Mart or similar No stock is fitted with any compressors. Its a pain when the loco changes ends. Several circular lines do (did) use train mounted compressors, the most notable being Lightwater Valley, the compressor of which was (and still is) mounted in the box van now at Cleethorpes with Little Titan. It is powered there by a petrol engine. |
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Craig Gluyas Talking to one's self is a sign of madness. I talk to my imaginary friend. | |
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| Andrew | 30 Apr 2009, 05:27 PM Post #8 |
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CME, Stackton Tressel Light Railway.
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The thing is David, if you are brought up on vacuum brakes (and lets face it, 95% of our heritage railways are) this is not normal practice. A drivers vacuum brake handle really only has two position. ON or OFF. ON, and the train pipe is open to atmosphere OFF, and the brakes are being drawn off by a vacuum. When the train pipe reaches the magic 21" or 25" of mercury the 'reservoirs' (if you can have a reservoir of nothing?) are being exhasted, charged filled or whatever you call it with a vacuum. Constantly putting a handle beyond 'running position' and into 'release' is not something to which your average volunteer footplate man is used too. |
| Andrew. | |
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| craiggluyas | 30 Apr 2009, 05:43 PM Post #9 |
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Except for those driving BR standards, DMU's or locos fitted with DMU valves..... |
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Craig Gluyas Talking to one's self is a sign of madness. I talk to my imaginary friend. | |
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| bvr379 | 30 Apr 2009, 05:51 PM Post #10 |
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With the main exception being the Romney, Hythe and Dymchurch Railway, most Miniature Railways probably use air brakes, because the components can be more compact than vacuum brakes, and off the shelf. Another issue is that quite a few Miniature Railway locos are newer than most mainline heritage locos. For example the BVR steam locos were biult in 1964, 1994 (x2), 1996 & 1999. In the last year, new steam locos have arrived at Perrygrove ("Lydia") and Cleethorpes (ROD). "Douglas Ferreira" arrived at the Ratty in 2005. (P.S. I worked on BR type air brakes from 1985 onwards!) Edited by bvr379, 30 Apr 2009, 05:53 PM.
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David Barnes Bure Valley Railway - The 15" gauge railway with powerful steam locomotives. Trains between Wroxham & Aylsham in Norfolk. Daily services between 24th March and 28th October 2018. Please look up the BVR website, for more details. | |
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| Andrew | 30 Apr 2009, 06:42 PM Post #11 |
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CME, Stackton Tressel Light Railway.
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Hi guys, I'm sorry if I've upset anyone, its not my intention. My apologies if I've got under anyone skin. I realize that the majority of miniature railways are air braked as opposed to their vacuum braked standard gauge cousins. It's not my intention to mix it all up. Correct education of any braking system is obviously paramount. Craig, at the risk of upsetting you. All the BR standards that I drove had the crudest vacuum brake valves, there is a one/two ejector valves (dependent on the number of ejectors) and a simple air valve. The brass air valve does look very grand on its little plinth, but at the end of the day its just a dump valve. The only vacuum brake unit I've ever known to come close to what were discussing (a running or lap setting) is the 'Dreadnought', but even then it doesn't actually do what its supposed to!!! The greatest problem with vacuum brakes are that they leak beyond belief. Most vacuum brakes on diesel locos do have a lap setting and all those that I came across all seemed to work. So you're right there Craig. |
| Andrew. | |
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| craiggluyas | 30 Apr 2009, 08:33 PM Post #12 |
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Hi Andrew! My bad. Thats what you get for making assumptions! I always thought it looked like it had 3 positions! You win some, you lose some... Interesting on the Romney with Vacuum brakes, as with long trains and no DA valves the front half of the train tends to apply long before the rear (especially on the 21 coach train we went on) meaning the rear half catches up with the front! One reason Vacuum never caught on! The other is sheer size. One only has to look at the size of the brake cylinders on the romney stock to realise how hard it is to get them in. Air cylinders working at 40psi have 3 times more force than the equivilant vacuum cylinder, meaning they can be 1/3 the size! Not so important on full size, but a god send when trying to fit them into a miniature bogie! Craig |
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Craig Gluyas Talking to one's self is a sign of madness. I talk to my imaginary friend. | |
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| Andrew | 30 Apr 2009, 09:32 PM Post #13 |
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CME, Stackton Tressel Light Railway.
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From a practical and theoretical point of view, vacuum brakes are hardly a sensible option. They have one factor, as far as I can see, that makes them so attractive to the steam loco designer. It is the single simplest piece of kit on a steam engine, no moving parts (with the exception of valves and non return clacks) theres nothing to go wrong. You open the tap and the needle goes up (or to be more accurate down). The system is so very simple, you suck the air out and the brakes go off, let the air in and the brake goes on... The draw backs, as Craig suggests, is you need some very large cylinders to get a good pull and the system is notorious for air leaks. Once you try to use vacuum brakes with a diesel loco you need an exhauster, if you're going to use an exhauster then you might as well use a compressor and have airbraking. Oddly enough, the air pumps that were so temperamental on steam locos are not the issue on smaller steam engines. The idea of a axle driven compressor and even more so a battery power compressor show some incredible lateral thinking which I find fascinating. It's a definite case of someone working out the boundaries needed for their continuous brakes and finding the simplest solution for their needs. well done.... And the idea of an initial charge to a reservoir from a 'land line source' that can then be sustained from an axle driven compressor is an obvious refinement. Is the compressor on St Egwin mounted in the tender or loco? I'm guessing the tender, so I'll probably be wrong..... |
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| craiggluyas | 30 Apr 2009, 09:37 PM Post #14 |
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I'd say an educated guess there.....! |
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Craig Gluyas Talking to one's self is a sign of madness. I talk to my imaginary friend. | |
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| glastonrail | 30 Apr 2009, 09:51 PM Post #15 |
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Dommo
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And injectors don't work on a similar principle.. ..? No internal moving parts, water cools steam to form a vacuum, which increases velocity of both steam and water, pushing up delivery pipe, turning into a force against clack valve... .? The last bit is the really interesting and clever part of the physics involved, which even I dont fully understand... ... Dom
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| "There's no such thing as sanity, and that's the sanest fact" M. Knopfler, 1985 | |
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9:18 AM Jul 11