Flying Scotsman

I'd have thought that a self tightening wrench like a bathroom plugwrench would be a very useful tool - don't know why there aren't many more variations on this theme.

 

Hey, we've got one of them at SRM and I have always avoided using it. I might give it a try in future if they are that good! I just find you have to be very careful how you use 'adjustables', tightness and direction, never mind which bit not to hit with the heavy hammer!

 

Only when on maximum cutoff, which is for hard work hill climbing and maximum acceleration. As I understand it at high speed the cut off is reduced to about 15% limiting the amount of time the steam is allowed into the cylinder and thus increasing the expansion and the efficiency. The pressure at the valve may be close to boiler pressure, but not in the cylinder. To pull a load of say 12 coaches on the flat would take the same amount of power and thus load on the frames whether the loco had 225 or 250 psi.

 

With decent valve events, even with a short cutoff (but full regulator) the pressure in the cylinder for the early part of the stroke will be not much below boiler pressure. Therefore the peak stresses on the rods, frame etc, will be proportional to the boiler pressure.

 

I don't think you are properly grasping the situation. Yes, it needs the same force to move a load along whether it has 225 or 250 psi. However, if the force produced by the loco is greater than the force required to move the train then it will accelerate. If the pressure is higher and all other things are equal, the force will be greater and the rate of acceleration will be greater.

 

I was talking about steady state situations, such as steady speed along a steady or negligible gradient.gradient. In that situation either the loco has to be notched up, or the regulator partially closed to maintain the steady speed.

 

Isn't your worst case/maximum load situation likely to be when the locomotive is *decelerating* climbing a significant gradient?

 

Yes I imagine a Mole bite is quite nasty, grip them more gently in future....

 

Some interesting points being raised. It seems to me that the main benefit of a higher pressure (and here I am talking about a comparatively small increment, not a high pressure of the order of Fury etc), is that the loco can run with a shorter cut-off with the same load, which should mean that it operates more efficiently as it can take greater advantage of the expansion. The difference in temperature of water boiling a few degrees higher at the higher pressure is small, and is swamped by the superheating effect. The extra pressure could be used to pull greater loads or to accelerate faster but there are then other factors which come into play such as adhesion and wheel diameter. Now, if two locos with different pressures are both taking a train of six coaches from, as an example, Grosmont to Goathland, other things being equal the cylinders, motion, valves gear and frames all have to cope with the same amount of work. However, as noted, the peak forces are likely to be greater on the higher pressure loco (while steam is being admitted). This is an advantage of compound locos: they work with longer cut-offs and lower pressure/temperature drops in the cylinders, thus there is a more uniform force being applied. So in theory, a Q6 with 180psi, operating at a longer cut-off, should punish itself less than a 225psi Black 5. Now this is partly offset by the larger piston diameter of the Q6, but my maths suggest that the peak force on the Black 5 piston is still greater, assuming full boiler pressure - which may not be the case if the regulator is not fully open, and the larger wheels and lesser adhesive weight of the Black 5 may mean that in practice full boiler pressure cannot easily be applied. Again in theory, the Q6 should use more coal but there may be a trade off between cost of fuel and wear and tear. This also raises the issue of whether there is any real benefit in keeping the pressure of locos on heritage railways at the original figure, as downrating them 25psi or so may not make much difference to their haulage capabilities and should lead to maintenance benefits.

 

These last contributions are all argumentative. Is anyone aware of Prof. Hall 's simulation package Perform?
It generates indicator figures and supplies numbers. It can be downloaded from the 5AT website.
Kind regards
Jos Koopmans

 

Just how big a job is it to reset/ fit different ( ?)Safety Valves to a lower pressure ?

 

I don't pretend to understand these technical points in detail, but this sounds a bit like the sort of thing Tuplin used to say, and when he presented a paper on those lines to the Institute of Locomotive engineers he got somewhat savaged by the likes of Ell, Holcroft and Carling.

http://www.steamindex.com/library/tuplin.htm#tupboilcrit

 

Inside a Ross pop safety valve is a threaded adjusting disc (it is a bit more than a disc). This is used to adjust the internal rectangular section spring until the correct blowing-off pressure is reached. When this has been done a seal is applied to the top of the safety valve to prevent anyone playing with it.
For example, the safety valves used on BR Standard locos can be set to blow-off at 200lbs, 225lbs or 250lbs pressure, depending on the maximum boiler pressure for the Class of loco they are fitted to.

 

Fairly simple then - But as its a piece of safety equipment then presumably any change made must be observed and checked by, or carried out by a comps person.
Sorry to ask mr standard but if you wanted your pressure set at 220lbs this would require a non BR standard valve ?

 

Correct on the first point.
The valve could be set to blow-off at 220 lbs, if that is the requirement.

 

I've just had a quick look as the steam tables. It only takes slightly more heat to boil a Kg of water at 250 psi than it does at 225 or 200. If you then go on the superheat it to say 350 degC, the higher pressure steam actually requires less heat per Kg than the lower pressure steam.

It goes without saying that higher pressure steam can do more work.

 

It was quite common to reduce the pressure of boilers at the behest of the Boiler Inspector and still happens today if he has concerns.. 60007's boiler pressure was reduced towards the end of its previous term of use. Going down is no problem , unlike going up! If you want to reduce the pressure through your own decision, that is not a problem and wouldn't even need the agreement of the Boiler Inspector..

 

Indeed at least one if not both Bullied design Pacifics for the Southern Railway and I think Hawksworths' County class 4-6-0 for the Great Western, started life with a working boiler pressure of 280 p.s.i. In all cases' the pressure was reduced to 250 in the fifties.

 

But it was not supposed at Doncaster that the higher power cracked the frames, it was put down to flexing at slow speeds on shed curves (And around places like Kings Cross and Newcastle. I expect). Flying Scotsman undoubtedly has A3 frames, but the A1 frames cracked as well, even before they were rebuilt to A3's. If anything the severity of the cracking reduced after they were all A3's, but that was almost certainly due to better repair and reassembly techniques at Doncaster. There was some limited redesign , moving of lightening holes etc. that might have helped too. FS will have all of these modifications. All of this is covered by the RCTS in some detail.

By the time that the A3's were being fitted with A4 boilers I would suggest there were two good reasons not to use the higher boiler pressure - first trains had got shorter not longer so the higher power was not really needed and secondly as well as the A4's there were 50 substantially more powerful A1's and an assortment of A2's if extra power was in fact needed. The reduced boiler pressure may also have somewhat reduced maintenance costs of the boiler, which is why it was done with the amply powerful Bulleids and Counties. There is no point in having more power than the traffic requires.

The Kylchaps were fitted to improve reliability and economy, not increase power. although they did, of course.

 

Hi, does anyone know the whereabouts of 60103 at the moment?

The reason I ask is that I am taking a small group of disabled young adults to the NRM tomorrow (Thursday), and I don't want to tell them it may be there, only for them to be disappointed.

Thanks
Dave