pault
Elder Statesman
Posts: 1,496
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Post by pault on Dec 24, 2018 20:54:16 GMT
I guess it all depends on your style of firing, and as with everything there is no right answer. Personally I dislike having one small injector that you leave on most of the time. Its to easy to just leave it on and, when you have a lighter or heavier load than usual, end up with the water too high or low. My preference is for two similarly sized injectors that are used intermittently.
The loss of one is far less of an issue as well. IIf you have a large and a small injector and the big one fails it can be a real handicap to carrying on to a convenient point where you can sort the problem.
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Post by delaplume on Dec 24, 2018 21:08:58 GMT
Well done Pete--------make that one more on order......"Happy Christmas" to me ..
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Post by Deleted on Dec 24, 2018 21:22:37 GMT
Thanks, Paul.. I hadn't thought of it like that...I guess it depends on the pressure range available from said injectors... I mean you don't want to be in a position where both the water level and boiler pressure are low ( below the injector operating pressure).. with no other form of getting water in ( I do, however, have a contingency plane for this), this sounds a little risky although perhaps not insurmountable as the fire would probably be very low too. As for style of firing, I want to follow full-size Pacific as closely as possible, I know how it's supposed to be fired and will try to emulate that adapting where needed for a smooth/efficient running model.
Currently, I'm edging towards low 20's injectors, they both need to be able to perform on the same sized pipework... I'm still reading into this, not had a chance to go back through Don's notes yet, he may well list the injector sizes to be used.
Cheers
Pete
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Post by Cro on Dec 24, 2018 21:23:55 GMT
I guess it all depends on your style of firing, and as with everything there is no right answer. Personally I dislike having one small injector that you leave on most of the time. Its to easy to just leave it on and, when you have a lighter or heavier load than usual, end up with the water too high or low. My preference is for two similarly sized injectors that are used intermittently. The loss of one is far less of an issue as well. IIf you have a large and a small injector and the big one fails it can be a real handicap to carrying on to a convenient point where you can sort the problem. With you on this, I think two 16-18oz should be more than enough. I don't know of any of our big 5" locos having anything more than this. The 10x I had on the 9f was more and I think it was a bit too much at times, killed the pressure despite throwing the water in damn quick. Adam
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Post by delaplume on Dec 24, 2018 21:34:38 GMT
Hi Pete,
I must admit when initially designing The Bear my original intention was to fit the same injectors as on the Castle / Kings BUT}---the mention that grate area plays a part in their selection convinced me to buy the book----Alas will now have to wait untill after the Hols....
Incidentally the nearest commercial grate that ALMOST fits is for the Duchess...( care of Blackgates ).....I needed to remove 1 longitudinal bar to make it fit into John Ellis boiler.....
How do I convert the quoted "fluid ounces" into "Pints per min." which is what the suppliers seem to use ---eg}-- a No.3 = 3/4 pints per min..
Alan
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Post by delaplume on Dec 24, 2018 21:42:43 GMT
I guess it all depends on your style of firing, and as with everything there is no right answer. Personally I dislike having one small injector that you leave on most of the time. Its to easy to just leave it on and, when you have a lighter or heavier load than usual, end up with the water too high or low. My preference is for two similarly sized injectors that are used intermittently. The loss of one is far less of an issue as well. IIf you have a large and a small injector and the big one fails it can be a real handicap to carrying on to a convenient point where you can sort the problem. With you on this, I think two 16-18oz should be more than enough. I don't know of any of our big 5" locos having anything more than this. The 10x I had on the 9f was more and I think it was a bit too much at times, killed the pressure despite throwing the water in damn quick. Adam Hello Adam, I seem to remember that when we had 70000 at Bridgnorth ( many moons ago admittedly ) I'm sure it had 1 off 8X and 1 off 10X fitted .......We were machining new delivery cones at the time and needed to get the correct one in the correct body.... the body being the same for either due to GWR standardisation..
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Post by Deleted on Dec 24, 2018 21:50:12 GMT
It's been a while but isn't there 20 oz per pint, so 3/4 pint = 15 oz... forgive me if I have this wrong...been filling my head with figures today so may not be thinking straight...BTW the size of the grate is new to me too, well to be fair it's all new to me...4472 has a large grate so something else to take into account...
Pete
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Post by delaplume on Dec 24, 2018 22:03:38 GMT
It's been a while but isn't there 20 oz per pint, so 3/4 pint = 15 oz... forgive me if I have this wrong...been filling my head with figures today so may not be thinking straight...BTW the size of the grate is new to me too, well to be fair it's all new to me...4472 has a large grate so something else to take into account... Pete Hi Pete, have just done the obligitory "Google" search and you're quite right}-------- UK }----- 1 pint = 20 fluid ozs Simple maths from then on !! Cheers Alan
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Post by Deleted on Dec 24, 2018 22:11:42 GMT
I double checked with my wife, her answer was to check the measuring jug...
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Post by delaplume on Dec 24, 2018 22:23:56 GMT
Just for interest sake but I read somewhere that a Duchess on full song / load ( up Shap for example ) can generate approx 3,000 HP !!.....and that's all due in the main to a well designed air flow route keeping those coals incandescent on the grate.....followed by an equally well-designed exhaust passage and a balanced valve gear giving good steam distribution allied to a minimal back-pressure on the pistons....
I would imagine that if you did some research into the grate AREA of all the British Class 8P Pacifics you'd find they weren't that much different...after all it's here on the grate itself that the power is first generated...and from here also the required performance of the injectors can be calculated ( Thus getting me neatly back "on-thread" as well !!).....
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Post by delaplume on Dec 24, 2018 22:24:39 GMT
I double checked with my wife, her answer was to check the measuring jug... LoL !!!
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Post by delaplume on Dec 24, 2018 22:28:53 GMT
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pault
Elder Statesman
Posts: 1,496
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Post by pault on Dec 24, 2018 23:00:35 GMT
Just to throw a few thoughts out there. Relating injector size to grate size is probably an attempt to match the objector to the maximum steam production rate of the boiler. Not necessarily a good thing If you don't operate at anywhere near 100%.
Dont confuse operating pressure and delivery rate or flow. Just because an injector can operate at a high pressure does mot mean it has a high flow rate.
A lot of people proudly tell you their injectors will work down to 20 psi. In reality this is not much help. If the pressure is that low you probably have the following, little water in the boiler, are incapable of moving, have bugger all fire, an ineffective blower and a thunderbird on the way.injectors that will at very low pressures are actually not that helpful.
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Post by mutley on Dec 25, 2018 9:34:19 GMT
Gordon Chiverton made a 24oz H/J 'Exhaust' steam injector for the A3/4. I run 20oz on my 2-8-0 Nigel Gresley 01 without an issues.
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Post by Deleted on Dec 25, 2018 9:50:57 GMT
thank you mutley, that's very helpful.....ty
Pete
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barlowworks
Statesman
Now finished my other projects, Britannia here I come
Posts: 874
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Post by barlowworks on Dec 25, 2018 10:43:51 GMT
Hi Pete
I have two 24oz injectors from Pavior Steam in stock ready for my Britannia. I got two the same size based on the idea that if one fails the other should do exactly the same job. I also have a Hewson exhaust injector casting that I am going to try and modify as a cover for the injector on that side. Should be interesting.
Mike
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Post by Deleted on Dec 25, 2018 13:13:33 GMT
Thanks Mike...
I've had another browse through Don's words but can't see anything...at least not that's easily found under a sub title...I'll keep looking...I know a few people with Doncaster on FB so will ask them too..
I think 24 oz fits in with 3/16 pipes too, i think it's wise to keep within the vintage published tables which seem universably accepted today.
Cheers
Pete
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stevep
Elder Statesman
Posts: 1,070
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Post by stevep on Dec 25, 2018 13:23:44 GMT
In the UK, there are 20 ounces to a pint, but in the US, it’s only 16
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Post by Deleted on Dec 28, 2018 19:47:21 GMT
Hi Guys
Just to bring things up to date of where I am in the thinking process (lots more to digest)...I have read through Derek's relevant sections on choice of injector sizes and afraid that I have discounted said advice as it's out of step of, well everyone else? Having now received Bob's pamphlet which I have to say is much more user-friendly and looked through his charts I think that I'm close to what 'Doncaster' needs. Bob's info is also backed up by advice given elsewhere including in this thread.
So where am I?
well for water pipe it needs to be 3/16 OD, all sources say this including Derek's, so 3/16 it is... Steampipe will be 5/32 OD... again this seems to be the size agreed on by most. Injectors, I'm going to go for two sizes which will be very close, Bob states for a 5" Pacific to use 22fl/oz for injector 1 and 28fl/oz for injector 2, I will go with these sizes or as close as I can make them. Although Bob doesn't give a lot of info re making injectors, he does give the required delivery cone, combining cone and steam cone sizes for each size. Derek's book is invaluable for the construction of the injectors.
In Bob's book, he talks about a testing rig he used for over a decade to confirm the sizes of injectors required, I will need to make a test rig at some stage. Bob talks of a Quasi check valve by Bill Carter, on reading his notes this looks like a great piece of kit, does anyone have a drawing for this valve that they are willing to share, also is it possible that Bill did a write up on this valve in one of the ME mags? I'd be very interested in getting a copy of this too if it exists.
If anything changes I'll, of course, give details but I think what I have here is a good starting point, I don't think that a few oz's one way or the other will make much of a difference.
Thanks for everyone's help and please feel free to comment further...
Pete
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don9f
Statesman
Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
Posts: 960
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Post by don9f on Dec 28, 2018 20:57:17 GMT
Hi Pete, is “scale” pipe size important to you? I don’t know anything about pipe sizes on Flying Scotsman, but I chose pipes for my loco based on the full size 9F:-
3/16” for the injector steam pipes (2” full size) 7/32” for the injector delivery pipes (2 1/4” & 2 1/2” for the live / exhaust steam injector deliveries) Ditto for the water feed pipes on the engine 1/4” for the water feed pipes on the tender (2 3/4” full size)
At the time this was in complete ignorance of any recommended sizes and always worked well!
Cheers Don
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