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Post by Deleted on Aug 17, 2013 20:47:14 GMT
Hi Guys
Well I have 4470 back together and now want to look into one of the suggestions made for improving her running....
It was suggested to me that perhaps the blast nozzles of 4470 need changing, reason given was to increase the draft from the fire although I need to check that I had no leaks anywhere first and I'm not very happy with her grate but will have to live with that for now. I know little of these things so would like to ask for advice from those more knowledgeable than myself. 4470 is twin nozzle, she has proper petticoats, nozzle holes are drilled No.20 size or 4.09mm standing around 1 1/2" from the base and has two copper rings above the nozzles each with 3 holes for the blower.
So my question is.. assuming that there are no other reasons for the drafting not being sufficient( if indeed that is the case) what should I be experimenting with... larger blast nozzles holes of smaller?
regards
Pete
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Post by Deleted on Aug 17, 2013 22:00:41 GMT
Hi Pete,
If anything, the nozzles are a bit small for the diameter of the cylinders. A quick calculation shows that 0.1875" or 4.76mm suits the cylinders better. However, it all depends on the rest of the system i.e. the dimensions of the petticoat pipes and the distance of the nozzles from the top of the flare on the petticotes. I've found that quite often the chimneys and liners are far too big in diameter compared to the nozzles and their distance apart too great and consequently the draughting is poor.
Is the draughting to the drawings? If so, I'll have a look at it and see if it is any good. I've considerably improved the draughting of quite a few locos now by using the ideas of Harold Barton.
John
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Post by Deleted on Aug 17, 2013 22:54:08 GMT
Thanks John.. That would be very helpful... I haven't taken the nozzles off yet to check if they are to drawing although there was a spare in amongst the bits and pieces box which I have measured and that one does seem to be to drawing at the sizes I've given... I'll take the nozzles off tomorrow and check to see if they are the same as the spare. If you feel they should be bigger John I'll happily follow your lead.... Many thanks Pete
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pault
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Post by pault on Aug 18, 2013 0:20:28 GMT
Hi Pete With respect I would either wait until you have a bit more experience of keeping a loco running or get someone with a fair bit of experience to give you a judgment on how the loco runs, before you change anything. A change of coal can result in the need to change the blast nozzles but the changes generally are relatively small. Making the nozzles bigger will soften the blast resulting in less draw on the fire. Making them smaller will sharpen the blast giving more draw on the fire. With any loco there will be an optimum way to drive it, i.e. a thick fire, thin fire, wound back lots or wound back a little. You need to test a loco under the conditions it will be running under. Some of our locos struggle a bit when running light engine or with a light load. put 3 or 4 coaches beind them with 12/16 people on them and they are happy. With a single chimney I would calculate any change in the nozzle diameter so that it gives no more than a 10% change in the area of the blast nozzle. As you have 2 nozzles you should calculate the change of area per nozzle to be no more than 5%, which will be a fairly small change in diameter. Hope this is of some help Regards paul
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jma1009
Elder Statesman
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Post by jma1009 on Aug 18, 2013 8:29:14 GMT
hi pete,
i would endorse paul's very wise comments (and re coal remember the story of Henry The Green Engine and welsh steam coal!)
the draughting on my locos is arranged to be optimum with a load, otherwise with a load and too small a blast nozzle the loco will go berserk with the safety valves blowing off all the time and resort to leaving the firedoor open all the time.
i would however check that the blast nozzles are in line with the petticoat pipes and concentric... if not they may need to be opened out, not made smaller. lots of variables to consider.
ive seen people break up large lumps of coal to put in the tender and all the crap dust and broken pieces of different sizes get chucked in - i break my coal up at home before running and it gets sieved and sorted and graded and only uniform lumps of the right size for the loco go in the tender.
quite a few clubs use anthracite beans for the 3.5"g locos which is designed for hopper type domestic stoves. lovely uniform size and graded, but anthracite needs a touch on the blower usually, especially without a load.
my introduction to locomotive driving when 16 included not long after being in charge of a 5"g loco (equivalent size to Heilan Lassie) on a portable track at an exhibition and hauling 12 adults all day long from 10am to 5pm, the queue for rides being never ending. 'there and back twice' (to see where you've been!), quick change of passengers, then off again.
cheers, julian
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Post by Jim on Aug 18, 2013 10:38:40 GMT
I'd agree with Julian that a check of the alignment of the blast nozzle to ensure the blast is central to the chimney is a simple job to do and may reveal some surprising results, as I discovered with the Burrell. Jim
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Post by Deleted on Aug 18, 2013 11:35:26 GMT
Thanks everyone for the help and advice...I've just checked the alignment.. that is certainly off... front chimney is in-line but back one isn't and I can't see any way of correcting this as it seems that the spacing between the chimney/nozzles if different. I guess I could design another nozzle for the rear that is offset to align with the aft chimney hole, although do I really at this stage want to spend the time involved to do this,I'll take a closer look at this later and see how things work out. Interesting comments on the coal.. I am indeed using Anthracite that was obtained from the club although I have the larger size as it was bought mainly with 5" in mind ( I will get a bag of beans as well) and I probably am guilty of having too much dust mixed in so will certainly correct that. I had already discovered that 4470 performed better with a little blower on as Julian suggested. As Paul also states this part of the problem is down to me in firing... my mentor at the club that day was always telling me to put more coal on.. I was resisting this a little trying to emulate what I had read in the 'Handbook for Railway Steam Locomotive Enginemen' which instructed how a fire should be managed although admittedly this is for full size it all seemed to make sense to me... light even fires with small quantities fed no more than fist sized( another reason for getting the bean sized coal). As you can see I have a lot to learn.. but how I love learning new things.... Pete
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Post by Deleted on Aug 18, 2013 12:41:46 GMT
Hmmm.. ok belay that last piece of miss-information... last night when i looked at the alignment of the nozzles I was convinced that they were out of line, today I thought i'd take a closer look using a torch. Having first looked i then used two suitably sized pieces of rod to fit down the nozzles... as you can see they are actually in-line. Note to self never look at things late at night in the dark.. so things may not be as bad as i thought, at least I can cross miss-alignment of nozzles off my list.... Pete
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jma1009
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Post by jma1009 on Aug 18, 2013 18:03:23 GMT
pete, for firing, a hot fire is a 'red' hot fire (usually seen as yellow/orange). what you should aim for with Heilan Lassie's shallow firebox is a uniform fire thickness which is fired 'little and often' (which requires firing 'on the run') so that the fire is ideally orange with a sprinkling of black coal on top that will soon catch light. a black fire produces very little heat (especially bearing in mind that most steam is produced around the firebox which transfers most of the heat from the fire by radiation). a thin fire requires less pull on the fire to keep it burning and hot, but far more skill to fire. the techniques used for a deep firebox (even in miniature) wont apply to a shallow large grate such as Heilan Lassie's, so i think your 'mentor' was giving you dud advice. cheers, julian
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Post by spamcanman on Aug 18, 2013 19:00:16 GMT
Pete, If your using the club coal do you know where they purchased it was it the local yard down the road that they used to buy from if so it's poor quality they did buy welsh steam coal a few years back but so many helped themselves it soon ran out. I always buy my own welsh steam coal and never had firing problems and when I have gave a bucket to others they have always commented how good my coal is.
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Post by Deleted on Aug 18, 2013 19:02:26 GMT
Thanks Julian... as I said I was trying to resist the 'more coal' syndrome... I have now tackled most jobs on the list.. refitted top to tender where I had been fixing the water pump... Checked nozzle alignment.... I take on board that I should gain a little more experience before changing nozzle sizes but would be very interested in John's calculations that can guide me if after getting more experience with 4470 she still has firing issues which I fully accept are probably more down to me than the loco herself. ground a bit of the fire-door.... this wasn't fully closing (although only slightly ajar) and very stiff...yes I know another possible reason for poor firing.. fitted handle to fire-door.....will be easier to open and fire on the run replaced broken motion parts to drawing.... made a larger shovel ( another suggestion from mentor) including a flattened end that fits the new fire-door handle... I should find firing on the run a lot easier now.... Kind regards Pete
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Post by Deleted on Aug 18, 2013 19:04:51 GMT
Hi Tony
I think it's new stuff as Mike said that they had had an issue with poor coal in the past and that this stuff was better.. I'm afraid that's as much as I know about the coal.
Pete
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jma1009
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Post by jma1009 on Aug 19, 2013 8:39:44 GMT
hi pete,
just a quick note re harry barton's articles referred to by john. i couldnt make much sense of them in 1989, and having re-read them last night they still dont make much sense. however he did fine tune a double chimneyed 3.5"g rebuilt patriot which may be of interest to you. harry goes about things in completely the wrong way IMHO. the main success he achieved was in correcting locos which hadnt been built to the Greenly 1:3 rule. as a result his findings werent that surprising for i have done exactly the same myself to lots of locos. however one needs to have an appreciation of the whole of the steam and exhaust circuit, an understanding of what would be a loco's optimum performance (which includes such matters as whether the loco has a good valve gear, superheaters, and whether the loco can be 'notched up', and the gas flow area through the boiler tubes and grate, and boiler proportions, and steam and exhaust circuit proportions). mucking about with a SPEEDY with small exhaust pipes, a BUTCH with 5/16" dia boiler tubes, and a 2.5"g loco of unknown quality dont constitute a very thorough or scientific approach in my book!
my approach with draughting has been to increase the size of the blast nozzle as much as possible to reduce back pressure yet maintain sufficient exhaust that the loco steams at its optimum level for a certain type of load where the grate isnt 'overloaded'. for prototype locos with long chimneys this is quite easy - the problem comes when trying to fit the Greenly formula into a 'modern' passenger loco with a short single chimney. similar problems were encountered by Sam Ell at the Swindon testing plant.
harry omits a vital piece of evidence which is that the pressure of the exiting exhaust ( before exiting from the blast nozzle) is much less than in fullsize. this is why i have always tried to ensure a free exhaust circuit from the moment the exhaust steam starts to leave the cylinders. the angle of the steam as it emerges from the blast nozzle may be the same, but if its speed isnt impeded by a restricted exhaust circuit then one can have a larger blast nozzle and faster flowing steam exiting from the blast nozzle will create a greater vacuum.
i wasnt impressed that the SPEEDY he modified ended up with a 1/4" dia blast nozzle. 5/16" dia would be the sort of size i would expect with a 'fine tuned' loco of that size! if one takes the view that harry's results resulted in blast nozzles that are too small than can actually be obtained (as i and many others have done) then his results are of little use.
for fire grates i have used the SMEE standard of 3/32" bars with 1/8" spaces, or 1/8" bars with 5/32" spaces. most of the stainless welded grates i have seen have insufficient spaces between the bars IMHO.
cheers, julian
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jma1009
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Post by jma1009 on Aug 19, 2013 9:03:33 GMT
as a further aside,
brian hughes of the birmingham club (of miniature vacuum brake fame) did some much more useful experiments than harry barton. i will have to look through my ME's to find out when. he told a most illuminating story of a visit to the Swindon test plant with a loco under test, and Sam Ell held a lighted cigarette up to the top of the chimney. the cigarette smoke was sucked into the smokebox down the chimney- indicating incorrect draughting!
don young , if a miniature loco was being tested on air, would take a more than larger drag on his cigarette and blow it through the fire hole door to see it exit from the chimney. whether this proved anything to don im not too sure, other than it gave him an excuse to smoke in someone else's workshop!! we all thought it signified something special and scientific at the time!
cheers, julian
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Post by Deleted on Aug 19, 2013 12:54:04 GMT
Julian - all I can say is that I've used Harry's ideas on at least five locos with significant results. Works for me but each to his own John
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elly
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Post by elly on Aug 19, 2013 15:31:00 GMT
Julian , an interesting version of how I test my gauge 1 locos , is to use a lighted cigarette lighter at chimney level if the flame is sucked into the chimney then its wrong. a very simple test. Regards Steven as a further aside, brian hughes of the birmingham club (of miniature vacuum brake fame) did some much more useful experiments than harry barton. i will have to look through my ME's to find out when. he told a most illuminating story of a visit to the Swindon test plant with a loco under test, and Sam Ell held a lighted cigarette up to the top of the chimney. the cigarette smoke was sucked into the smokebox down the chimney- indicating incorrect draughting! don young , if a miniature loco was being tested on air, would take a more than larger drag on his cigarette and blow it through the fire hole door to see it exit from the chimney. whether this proved anything to don im not too sure, other than it gave him an excuse to smoke in someone else's workshop!! we all thought it signified something special and scientific at the time! cheers, julian
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jma1009
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Post by jma1009 on Aug 19, 2013 16:48:08 GMT
hi john,
i am a great admirer of your work and articles. i hope you will agree with me that some of harry barton's comments in his article in ME in 1989 dont make sense and some are conflicting. all one has to do is apply the Greenly formula. how one decides at the correct petticoat pipe choke diameter, and the correct blast nozzle size for a given loco is a different matter entirely, and this is where i disagree with harry barton who uses a percentage of cylinder diameter to work out the blast nozzle size and petticoat pipe diameter.
this is far too simplistic. one needs to take into account lots of other variables, and other factors which are far more important.
for example don young, in his magazine LLAS, set down his own ideas based principally on free gas flow though the boiler, and was at pains particularly in his later designs to ensure that his free gas flow figures were generous, and that his steam and exhaust circuits were generous.
jim ewins was also of the view that the free gas flow percentage through the boiler was critical in deciding the petticoat pipe choke diameter, allied to the size of the grate. neither don young or jim ewins decided the petticoat pipe or blast nozzle sizes on the basis of cylinder diameter. jim also de-bunked those who suggested that slavish adherence to fullsize proportions would be 'superior'. (harry barton's table of BR standard designs would be an example of something jim would have disapproved of).
i have jim ewins' paper on this subject.
back pressure can have a startling effect on miniature locomotives because often the steam chest pressure is very low anyway to start with. if the exhaust steam has to be severely throttled at the blast pipe to get the fire to burn properly then there is something seriously wrong with the locomotives harry barton experimented upon!
cheers, julian
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Post by Deleted on Aug 20, 2013 1:08:58 GMT
Hi Julian,
Ok, I probably need to do a bit more research into this draughting business. I agree that free gas area through the tubes will have an impact on how the front end needs to be designed. I'd be interested in the articles by Brian Hughes - I'll have a look through the ME indexes.
I know Don's boilers were always said to be free steamers and I did work out the ratio of the tube area versus the grate area on his Black Five and Horwich Crab. Both are near enough 12% which I think is a good ratio (full size seems to be about 15%?). Hielan Lassie seems very deficient in tube area however with a ratio of about 7% which suggests it will need quite a strong blast to get enough gas flow. I worked on a 2½" LBSC Gwen Elms for a friend (we entered it in the Curly Bowl a couple of years ago - didn't come anywhere!) which has a similar low ratio of 6%. It was a real pig to even get the fire started and difficult to keep in steam without the blower on all the time. I'm sure the lack of tube area had a lot to do with it. Unfortunately both Gwen Elms and Lassie have combustion chambers which reduce the number of tubes that you can squeeze in.
With regard to basing draughting on full size - the V2 that I drove on Sunday had the original draughting scaled down from the full size double Kylchap using scale blast nozzles etc. It was a very poor steamer with a very soft blast until I modified it and fitted smaller blast nozzles and new chimney liners. I don't know what the tube area is like on that boiler as I don't have any drawings for the boiler.
Pete - I think I read that you were burning pure anthracite on your last run? If so, it might be worth experimenting and mixing some Welsh steam coal with it. One coal doesn't suit all locos. I normally use a 50/50 mix on 2½" gauge locos. The steam coal burns easily and keeps the fire going and the anthracite gives a bit more heat. Anthracite on it's own needs a good blast to keep it burning well.
John
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JDEng
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Post by JDEng on Aug 20, 2013 7:44:45 GMT
Anyone read "The Fire Burns Much Better...." by J. J. G. Koopmans?
The book is a thesis he did for a university course and looks at the issues surrounding front end design and draughting.
I have no practical experience of actually trying any of his recommendations but he seems to talk a lot of sense on draughting and some of it is aimed at miniature locos.
I got my copy from Camden Miniatures.
Regards,
John.
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jma1009
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Post by jma1009 on Aug 20, 2013 8:18:31 GMT
hi john (baggo),
as a hopefully interesting aside have a look at bob sanderson's article in ME 15th June 1984. jim ewins used bob's formula in his famous 'Jimmys Riddle' loco that he entered in IMLEC that same year.
bob makes the telling observation that 'since the same steam demand and hence draught required can arise from large cylinders at low speed or small cylinders at high speed it is illogical to proportion the blast nozzle on the cylinder diameter. it is preferably based on boiler dimensions'
don young's BLACK FIVE is one of his few designs where the free gas flow percentage is low. (the HORWICH CRAB may be similar but ive no experience of driving one - yet!) don young's No.1 RAILMOTOR boiler (1968) has a free gas flow percentage of 35% of the grate area, and will steam on a candle with the blast nozzle considerably larger than shown on the drawings (7/32" dia in my case) cylinder bore only 1 1/32". my 5"g GWR 0-6-0 loco has a free gas flow percentage of 25% of the grate area with a blast nozzle of 5/16" dia and only 1 3/8" bore x 2" stroke cylinders. (in the above calculations i have ignored the effect of the superheater elements). martin evans' BOXHILL boiler has a free gas flow percentage of 17%, and is of current concern to me!
i once had the option of buying a Jackson/Clarkson 3.5"g A3 unfinished but with a beautifully made boiler by a friend. when i saw the long boiler with only 3/8" dia tubes i decided it would be a hell of a job to get it to steam - in that case the free gas flow percentage was one factor but the length of those small tubes yet another. by the way jim ewins favoured a more generous tube diameter than one would arrive at by applying the Keiller proportions for length and diameter.
incidentally, we built a SUPER SIMPLEX as a club loco some years ago and i went over to don to get him to check the draughting arrangements - which i might say he did using a calcalator with me standing beside him and i was very impressed - he was a clever chap and knew what he was doing. he advised some subtle changes to the draughting but it was basically ok and he approved of martin evan's draughting arrangements. i still have his penned alterations to the drawings somewhere.
cheers, julian
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