MHR Restorations and Overhauls

Thanks for the last few posts, some intersting aspects, especially the Doncaster proposed mods, I will endeavour to get a copy of the book and read up a little more.

I can see some of you have some strong views , and probably a lot more experience of seeing the parts disasembled and how they fit together.

I will need to see some parts or drawings to establish the operational characeteristics, what bearings might fit and be sealed and how the main assemblys could be adapted.

It may not be feasable that's a possibility , but I would not be discouraged to continue my thoughts at this stage I would like to listen to some people who might have considered modifications before.

Thank You All for continuing to offer your thoughts and understanding on the subject.

Was the blast pipe/ chimney redesign to give better acceleration whilst holding a good head of steam and full boiler presssure, freer steaming ,as it will obviously pull harder on the fire, or more evenly, seperating the two beats, cleaner fire?, (I was not aware of a steaming fault with the boiler arrangement) ,intended better efficiency? Is there a view

 

Most of the passenger traffic on the LTS was in the hands of the 3 cylinder Stanier 2-6-4 tanks. The double chimney design for the Std 2-6-4 tanks was done in an attempt to increase the efficiency of the locos and give them a bit more oomph.

 

I guess from that they had a tendency on suburban work to loose head of steam and max boiler pressure on continuous stop start and slow speed running, where there was insufficient exhaust blast because of this to keep the fire in a good state and transfer it to the tube area , by adding the extra chimney they could balance the draught required to keep the heating surface balanced therefore getting the boiler back to its 90%-100% duty condition at full boiler pressure and hence giving it the full oomph.

 

Err..Yes. Then again, err....No!

 

"Empty pot"

Perhaps you would like to expand a little technically on how you see this mod altering the steaming.

How do you percieve the modification was supposed to improve or overcome an issue for LTSR operation.

if it is not the suggestions I made, fitting a double chimney increases throughput of burnt gases does it not.?

It depends where the loco designer originaly intended the boiler/ fire & grate duty cycle to be, was it at nominal 30-40 MPH constant running, if it was then the LTSR duty cycle was not well proportioned and I asume more draft was needed.??

 

I suspect this is is intended as a gentle hint that the original post seemed to be written in gibberish!

 

This projected mod is news to me, hadn't heard of it at all. Interesting though. I wonder if it was a consequence of the improved performance of the Cl4 4-6-0s with the double chimney? Earlier it was mentioned that the double chimney of the Ivatt Cl4 mogul was to be used which is a little odd.

There seems to have been much less managerial control over the doubling of chimneys. Swindon did the Cl4 4-6-0s, it was based on a double Dean Goods blast pipe, I believe. They also designed the external chimney, rather taller than the single. Eastleigh then applied the double blast pipe to some of the 4-6-0s and designed another chimney, the same height as the single. I'm not sure which of the survivors have the Swindon or Eastleigh design.

Lastly a plea the 'TheEngineer'. Your posts are most interesting and do please continue with them, but please could you phrase them in conventional engineering terms? Thanks.

Regards

 

Last sentence taken on board will do my best.

I believe that in order to improve the venturi of the chimney and thus the efficiency by using the final discharge of the discharging blast pipe steam, from the cylnders as opposed to just blowing lost steam up in the air. That chimneys were lengthened blast pipe discharge point relative to the controling dia within the venturi is important.

I do not know what conclusion the technical design teams in 1950's came to. But if I were assesing how to improve fire drafting flow at low speed the generation of vacuum/negative pressure, in the smoke box is an important aspect. I would have done the same, lengthen the venturi downward into the smoke box and upward into atmosphere..yes there is a limit on length and how efficient you can get it all.

Its a bit like metering the water into the boiler using axle or motion driven force pumps geared to the cylnder and valve possition to ensure everytime you use some steam you replace the water used to make it. As opposed to only using injectors to fill the boiler. With force pumps you can pre heat the water to almost boiling around the outside of the smoke box where heat is being lost generally.These issues may seem insignificant and over one day they are, but over 10 years they are not. Pouring cold water into hot boilers in my mind is non prefered, if you can pump in hot for nothing then that's worthwhile the energy used to make steam from cold water that injectors need to function is significant between 20c and 100c. These are all thoughts which can be adopted. Coal costs money and its not getting cheaper.

Good and well proportioned venturi chimney/blast pipe will meter the fire pull using the blast pipe discharge volume and pressure and nozzle design, to meter the fire pull. Its not an exact science but you can get it better or worse, depending on how you understand the venturi effect (and how it was taught) if you have a good feel for what your doing overall chances are you will tune it until your satisfied for the duty you want.

Its a bit like understanding carburettors, ignition timing, port layout and design with engine tuning how to make the engine give more torque as opposed to power. It needs to be right to win the race. Just pouring petrol in is not an answer.If you see my point of view.

 

Sorry I am not sure what was gibberish was it me writing something ?? people did not understand.

 

The first Class 4 4-6-0 fitted with a double chimney was 75029. The chimney was a grotesque fabrication, not a casting. As you say, the double balastpipe used was a GWR one. Brighton drawing office redesigned the chimney and produced a drawing for a new double blastpipe. All the castings were produced and machined at Swindon. The other 8 W.R. locos to receive double chimneys were converted at Swindon. The 15 S.R. locos had their conversions done at Eastleigh. 75029 eventually received the Std version in Feb 1960. It is interesting to note that the blastpipe caps used on all the conversions were the same as those used on the double-chimnied Kings , Castles and Counties.
The plan to apply double chimneys to the LTS based Std 4 tanks was nothing to do with the double chimneys applied to the Std 4 4-6-0s. The Eastern Region required more oomph from these tanks on the heavy, tightly scheduled LTS services.

 

The pumping energy losses are not significant in comparison to the energy used to heat the water. A pond pump is 100 w a pressure pump on a steam cleaner is 2500w thats 2.5kwhrs and pumps say 600 ltrs at 2500 psi pumping a tenth of the pressure 250psi about a sixth of the power. A kettle takes 2.5kw and boils 1 litre in 3 mins aprox, so 2.5 kwhrs boils 20 litres.The heat energy losses to heat water far out weigh in this situation. We are talking about quite a small force pump maybe an inch dia and 6 inch variable stroke (volume of steam to water 250-400:1 by volume depending on the level of super heat-its a long time since I used the ratio. Corrections accepted but it is a significant expansion ratio)

 

Thank you Std tank, your last sentence confirms my thoughts at low average speed stop start duty cycle the boilers could not make enough of the fire with standard draft to deliver the demand on steam for repetative acceleration purposes, where the energy needed is highest.

I suspect drivers were making a lot of use of the blower to overcome this, and pull sufficient heat into the tube bundle, from the grate there is little up draft through the grate from forward motion as anticipated, even with all the air ways open . The blower is using desperatly needed steam "to waste", on occasions even with the blower on they may have been often short of maximum boiler pressure and hence slow accelerating, moving all the trafic margins out. Against electric stock acceleration this would have been a big issue. Engineers would have been concerned about this issue and this drove the redesign requirement for LTSR I suspect. Phasing out of steam killed it, for this operation.

Overall water usage would have been up and the ability in schedule to refill the tanks was not always there, apart from it being a nuisance to crew. Is this a fair view.

 

Sounds like a good reason for someone to put together a Standard 5 Tank (4-6-4T)...

 

We're OT now, but this is an interesting subject...

There were experiments, even before Grouping, with feed water heating. Obviously they came to naught, but I wonder, why was that? A lack of reliable, compact, high pressure pumps? Complexity? Of course, fuel (and labour) weren't the percentage of total costs that they are today, so I wonder if THAT had a lot to do with things remaining 'as they were', just using injectors.

 

East German Railways fitted water pre-heaters as standard when rebuilding locos in the 1950s and 1960s (apologies if that timescale is wrong).

I am no Engineer, but the impression I get is that both sides of Germany, while building less totally new Steam Loco after the War, actually developed the technology of steam mainly through rebuilding war built and pre-war locos far more than we did in the UK. I suspect the BR Standard Steam Locos were a rare example of British railway engineers "playing safe" and not trying any too radical - an approach subsequently abandoned in the never ending quest to have the latest "toys"!

Steven

 

61624 has basically said what I was hinting at! Whilst I accept that not everybody is good at grammar, it does become more necessary when you are trying to explain such complex things things. After re-reading it several times, I think that I understand what you are trying to say, but pity the poor non-engineering folk amongst us.

 

As has been said, way off topic but very interesting, nevertheless.

I'm intrigued at the proposal to fit the Cl4 tanks with double chimneys. I've never thought of 80135 as being shy for steam; in fact quite the opposite. Double chimneys really only come into their own at high outputs, enabling adequate draught without excessive back-pressure at speed. At low outputs, they can be a positive drawback. This was especially so with the double chimney Cl4 4-6-0's and 75029 is a good example. On normal NYMR duties, its steaming ability falls short of the other BR standards that we have. I don't know too much about the LT&S road and the duties required of the tanks but, I'd have thought that a double chimney would not have been good on frequent stop-start running and would be best for the longer, high speed runs which, presumably, they also undertook.

 

Feed-water heating: I seem to remember that Drummond on the LSWR experimented with this quite extensively, but Urie dropped it in favour of superheating - IIRC, feed water heating gear added weight and complexity, required extra maintenance, but didn't give anything like the efficientcy improvement of superheating. I guess as technology improved, the trade-offs changed and it became a worth-while improvement in some cases.

Double chimneys & multiple blast pipes: IIRC, the big benefit is reduced back-pressure in the exhaust passages, so the live steam doesn't have to fight against the exhaust to push the piston. Doesn't back-pressure rise exponentially with speed? If so accelleration would fall off rapidly as speed increased - so I'd think it could be a useful improvement on an outer suburban service like the LT&S - depends at what speed the back-pressure starts to become a problem. Is back-pressure also a function of cut-off? If so, it would be more troublesome during accelleration or hill climbing than bowling along at express speeds. You also get a gentler blast over the fire (at least, with some designs), so it won't get ripped to pieces when the loco is working hard. On the other hand, I guess it's less helpful when your are trying to coax a shy steamer back into life.