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Post by Jim on May 28, 2015 13:47:46 GMT
As with full size I use reverse gear for braking when on a road run on my 3" Burrell SCC traction engine. It's effective and in fact the only way of controlling the engine.
Jim
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Post by Deleted on May 28, 2015 13:52:01 GMT
Being a bit thick can anyone explain to me how the valve gear becomes damaged if the transition from forward to reverse is made relativity slowly when related to the speed of the engine. As you move from full forward towards reverse the valve travel and velocity decrease to the point where there is little movement of the valve and the velocity is fairly low. A change from forward to reverse at this point should cause little distress. There is of course the documented damage to one of the leader power bogies when it when from forward to reverse however that was a sleeve valve set up with sleeve rotation as well and could be described as a troublesome design at the best of times. For that reason I don't think it counts in this situation. I would venture to suggest that people do not do it on railway locos for one of two reasons. A) mechanical sympathy with the loco, I agree with that.B) most loco wheels are braked adding additional braking force on the wheels is likely to result in them locking or rotating the wrong way which will have the effect of reducing brake force. A traction engine unlike a railway engine has more grip than power so significantly more brake effect can be put to good use. The valve gear damage story comes from a reported incident where a driver tried to stop a runaway engine with pole reverse by putting engine into reverse . Unfortunately he lost control of the reverser due to the violent motion of it before he could get it set and lock in position . The latch failed and until driver wrestled control back the valve gear was just slamming itself into different random settings as the wheels turned and major damage was caused . Note though that damage was not actually caused by reversing gear while running forward but by an incidental mishap .
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steam4ian
Elder Statesman
One good turn deserves another
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Post by steam4ian on May 29, 2015 23:42:50 GMT
Steam engines in steel hot rolling mills were always fitted with instant reverse valve gear - the mill rollers could not be allowed to be stopped on the plates or rails being rolled both because an indentation would form and because the plate would be chilled locally to below acceptable rolling temperature .
Some steam rollers were also fitted with instant reverse for essentially the same reasons when laying Tarmac . [/quote]
Michael
I spent some happy years of my electrical engineering career working for steel mills. I never saw mils reversed with the bloom/billet still in them.
The only steam driven mill I saw was at Newcastle NSW (1970) and that was idle at the time (Damn it); that also was a plate mill.
Certainly the steam engine would have been braked and reversed by the valve gear as that would have been the only way for it to happen quick enough. Time is money and time is lost heat in the bloom/billet.
Thanks for the memories.
Regards Ian
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Post by Deleted on May 30, 2015 9:24:56 GMT
Hi Ian , Certainly the steam engine would have been braked and reversed by the valve gear as that would have been the only way for it to happen quick enough. Time is money and time is lost heat in the bloom/billet.
Thanks for the memories.
www.youtube.com/watch?v=kZjyKYvUQs012,000 IHP 720 RPM - terrible video but shows the size and construction of these engines . This may have been the biggest of all but there were many developing 5,000 + IHP . Usually verticals but there were some horizontals . Note that engine is running very slowly in video - hot plate rolling is a dramatic fast process and in actual use engine would be going at maximum speed for short bursts . Regards , Michael .
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Post by Deleted on May 30, 2015 11:13:20 GMT
Can't find a video of a traditional large plate or rail rolling mill but this is a bit about the modern process : www.youtube.com/watch?v=6xnKmt_gsLsIt was not my normal work but I did design two special purpose mill rollers a long time ago .
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Post by mhrvol on Mar 28, 2020 13:42:38 GMT
Could somebody please explain the function and purpose of the 'lap' position on a combined steam an brake valve ? Thanks in advaance
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uuu
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Post by uuu on Mar 28, 2020 14:13:37 GMT
If you move the valve to the "apply" (or "on") position, the brakes will come on with increasing vigour, until the wheels lock up. If you want a less fierce braking, you move to "apply" for only a short time, then back to "lap". The brakes will then stay at that level. You can increase the brakes a bit by a further short movement to "apply", or let them off a bit with a short movement to "release" (or "off").
In a vacuum system, the apply position admits air into the train pipe, the release position sucks air out. Lap holds everything steady.
Wilf
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mbrown
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Post by mbrown on Mar 28, 2020 14:56:27 GMT
By the era of diesel locomotives, they had developed the "self lapping" brake valve. That meant that whatever position you moved the handle to, it held the brakes at a proportionate level of application. Used especially with air braking.
With an "on/off" steam brake valve, you can only hold lap for a short while as cooling and condensation cause the application to weaken so you have to keep topping it up by letting more steam in. The proportionate brake valve as on BR Standards, held a constant pressure in the steam brake cylinder. A vacuum brake valve placed in Lap should hold any given level of vacuum provided the system doesn't leak.
Malcolm
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robmort
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3.5" Duchess, finishing 2.5" gauge A3 and building 3.5" King
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Post by robmort on Nov 22, 2020 10:20:52 GMT
.... With an "on/off" steam brake valve, you can only hold lap for a short while as cooling and condensation cause the application to weaken so you have to keep topping it up by letting more steam in. The proportionate brake valve as on BR Standards, held a constant pressure in the steam brake cylinder. A vacuum brake valve placed in Lap should hold any given level of vacuum provided the system doesn't leak. Malcolm I've been looking into braking for my 3.5" King and wondering whether the steam brake would really be used and if it's worth the complication of making it, as most drivers on the club track seem to use only the carriage brake. If the steam brake is only used for parking, something simpler could be used. With regard to Malcolm's last comment "With an "on/off" steam brake valve, you can only hold lap for a short while as cooling and condensation cause the application to weaken so you have to keep topping it up by letting more steam in", on the King the steam cylinder has a feature I've not seen elsewhere that may avoid this problem, which is that the cylinder has an additional jacket that is always fed with steam to stop condensation in the brake. Does this help with the lap position and use of progressive braking?
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Post by Deleted on Nov 22, 2020 10:30:19 GMT
Hi Rob
I doubt very much that many use their engine brakes, be it steam or vacuum.... much better to use the driver trolley as you aren't then causing wear on the loco wheels. Mine will be fully working but only used to show that they do work, not for general running. The tender handbrake on the other hand will be used.
Pete
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mbrown
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Post by mbrown on Nov 22, 2020 11:48:17 GMT
Hi Rob,
The hotter you can maintain the steam brake cylinder, and the longer you can put off condensation in it, the more consistent the performance of the brake.
You only really need the lap function when stopping a train gently over a distance. But in our scales, stopping the train with the loco brakes is not easy as the weight of the loco is small relative to the weight of the train and the wheels can lock up very easily. It isn't easy stopping a full size loaded train with a steam brake either, which is why heavy loose-coupled trains would be slowed down gently with the tender handbrake until all the buffers were together before even considering using the steam brake.
Doug Hewson has written that he uses the steam brake on his Y4 tank (5"g) when shunting at the Gilling track where they try to do everything as protoypically as possible. But I guess the weights involved are commensurate with the brake power available. His steam brake valve design is a small piston valve which, I suspect, gives much finer control than the LBSC-style disc valve which can be very stiff to operate.
I have a similar steam brake on my Burma Mines loco, plus vacuum brakes for the train. I have used the steam brake to hold the train still when standing at a signal on a gradient, having stopped on the vacuum, and releasing the vacuum once the steam brake is on. You can then hold the steam brake on as you open the regulator to do a kind of hill start and prevent rolling backwards. But, to be fair, you can do exactly the same with the driving car handbrake!
Malcolm
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uuu
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Post by uuu on Nov 22, 2020 13:19:47 GMT
Passengers climbing on and off the trolleys can bump the train about a bit, so if you're just using the locomotive brakes (steam or wind-on) you get dragged about. Better to keep your train or driving truck brake firmly applied until things have quietened down.
Wilf
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