How to distroy a steamlocomotive with a wheel slip

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Bruce_Mowbray
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Re: How to distroy a steamlocomotive with a wheel slip

Post by Bruce_Mowbray » Tue Apr 01, 2014 7:26 pm

The first video, the Blue Peter Slip, looks more like a dry pipe failure or possibly a throttle valve break. The fact that the steam continues to flow without showing any signs of slowing down leads me to this. Most throttle linkage failures result in the throttle valve shutting. Even the balanced type of spool valve like to suck the valve to the closed position without some form of friction or quadrant teeth.

The second spin looks like a large slug of water may have entered the dry pipe and super heater elements. This water turns to steam and if the throttle valve is before the elements, this would cause a machinery runaway of this type. Either way the independent locomotive brakes should have been fully applied to keep things from running away as they did.

I have seen inexperienced crews freeze when something startling like wheel slip occurs. There is a lot to think about when things are going the way they should. When an engine starts slipping, the noise and violent shaking is enough to disturb the senses. Once the locomotive runs away, its already too late to think about closing the throttle, throwing down some sand, putting the reverser all the way in the corner and applying some engine brake before things really get rotating to the point of possibly doing some damage.

BTW, notching up can cause the runaway action to continue for a longer period of time than desired. Once the throttle is closed, the engineer wants to use of the excess steam as quick as possible. Short cutoff reduces the amount of steam being used on each stroke of the piston. Putting it in the corner uses up excess steam quickly and the wheels will stop spinning sooner, probably avoiding the machinery runaway situation. Even under way, running of the locomotive closer to the corner with the throttle closed a little bit, it is much easier to control wheel slip.
Bruce Mowbray
Springville & Southern RR
TMB Manufacturing & Locomotive Works

marshall5
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Re: How to distroy a steamlocomotive with a wheel slip

Post by marshall5 » Wed Apr 02, 2014 4:37 am

Bruce, I'm sure both of the scenarios you describe could produce the results seen in the video but in this case there was no failure of either the dry pipe (main steam pipe in UK parlance) or throttle (regulator valve) nor was there any water carry-over. As I said the loco slipped (as LNER 3-cylinder Pacifics are prone to do) but the driver was incapacitated by the spinning reverser handle (as he hadn't 'clipped' it) and unable to shut the regulator. Interestingly the loco's regulator handle used to be double ended so the fireman could have closed it from his side of the footplate but was modified for "health and safety reasons"! Unfortunately the whole incident underlined the need for the train operator's crew to be familiar with a particular type of loco's 'characteristics'. Ray.

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Dick_Morris
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Re: How to distroy a steamlocomotive with a wheel slip

Post by Dick_Morris » Wed Apr 02, 2014 5:20 am

why did the valve gear screw wheel take off?
Don't the screw reversers use a multiple start screw? If so, the crank would be more prone to free wheel when under pressure than if they used a single start screw.

marshall5
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Re: How to distroy a steamlocomotive with a wheel slip

Post by marshall5 » Wed Apr 02, 2014 7:26 am

Dick_Morris wrote:
why did the valve gear screw wheel take off?
Don't the screw reversers use a multiple start screw? If so, the crank would be more prone to free wheel when under pressure than if they used a single start screw.
Sorry Dick but I don't know if the A2's had a single or multiple start screw. A fatality at the North Yorks Moors Rly a couple of years ago was caused by the screw reverser on a Southern Rly S15 winding itself into forward gear. Unfortunately this went unnoticed by the driver who expected the loco to move backwards when he opened the regulator but instead moved forwards crushing the guard between the buckeyes of two Mk1 coaches. Very sad but the accident report highlighted the need to ensure that the reverser is always 'clipped' and observe the rules about not going 'in between' even when you expect the loco to be moving away from you. Ray.

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