|
Post by simplyloco on Mar 1, 2019 23:03:04 GMT
SNIP Reading it all is heavy going, brevity and injectors don't seem to be good bedfellows! SNIP Hi Roger. Agreed ! John
|
|
|
Post by simplyloco on Mar 1, 2019 23:08:53 GMT
SNIP Reading it all is heavy going, brevity and injectors don't seem to be good bedfellows! SNIP Hi Roger. Agreed! Especially when self appointed moderators intervene! John
|
|
|
Post by Donald G on Mar 2, 2019 8:40:19 GMT
Hi Roger, The proportions of your 'condensing cone' to 'mixing cone' are dealt with in Bob's EIM articles. They can also be analysed from the DAG Brown drawings in his invaluable book, taking into account the steam cone being inserted a bit into your 'condensing cone' for which all dimensions are provided as part of the 'annular' gap for repetitive work doing batch production. There are also other sources such as the Eric Rowbottom injectors described by Basil Palmer in ME. And Bill Carter's 'weeny injector' described by Laurie Lawrence in ME as part of his 'standard size' series, which Steve P has referred to in his post - Laurie's standard injector being a copy of the Arthur Grimmett and Ted Linden injector. To latch onto Bob Bransom, without considering others who went before, seems to me to be ignoring other evidence. The Eric Rowbottam injectors described in ME are quite relevant to a 16 oz per minute injector, and DAG Brown knew all this. So did Gordon Chiverton, who no one has yet mentioned, who arguably provided by the trade the most reliable and successful injectors in the UK, and his products are much sought after these days, as are the Arthur Grimmett injectors and Ted Linden injectors. Cheers, Julian I can vouch for Gordon Chiverton injectors as I have 2 on my Class 2 T. They are brilliant. Donald
|
|
|
Post by jon38r80 on Mar 2, 2019 12:22:44 GMT
Im not sure how the parts you have illustrated are supported by the casing they fit into but I immagine it is a effectively just a tube with ports in for air/steam and a pipe out for water so using a plastic would not seem counter intuitive as it would all be well supported and can be made to very fine tolerances. I suspect its not been looked at before as plastics available to the model engineer can be very limited, as with much of the other information you have presented, its usualy made of brass dictated by custom and practice . It's nice and easy to machine with model engineers tooling, readily available and proven to work. Much of the maths involved is a pain which most people dont want to entertain especialy when someone else has provided a nice simple table to follow. Hydrauilic and fluid dynamics was a bit of mental torture when I took it as part of my degree and only subsequently used it to set up a program that did the number crunching to design a water delivery systems for irrigation. I just fed the numbers in to my program and got an answer for someone else to engineer! pipe losses from bends do have a significant impact. Nice straight level pipes (no head to work against) are what we looked for.
|
|
|
Post by Roger on Mar 2, 2019 15:01:53 GMT
Im not sure how the parts you have illustrated are supported by the casing they fit into but I immagine it is a effectively just a tube with ports in for air/steam and a pipe out for water so using a plastic would not seem counter intuitive as it would all be well supported and can be made to very fine tolerances. I suspect its not been looked at before as plastics available to the model engineer can be very limited, as with much of the other information you have presented, its usualy made of brass dictated by custom and practice . It's nice and easy to machine with model engineers tooling, readily available and proven to work. Much of the maths involved is a pain which most people dont want to entertain especialy when someone else has provided a nice simple table to follow. Hydrauilic and fluid dynamics was a bit of mental torture when I took it as part of my degree and only subsequently used it to set up a program that did the number crunching to design a water delivery systems for irrigation. I just fed the numbers in to my program and got an answer for someone else to engineer! pipe losses from bends do have a significant impact. Nice straight level pipes (no head to work against) are what we looked for. Hi Jon, Yes, the parts will be fitted in a sleeve, which itself is then fitted into the scale body like others have done. This means you can create passages and trap little disk valves in spaces created for them. I too don't wish to revisit the maths, I'm more than happy to take the various throat diameters from a graph that someone else has put a huge amount of effort to create. One thing I'm struck by is the abundance of dimensions available in the form of tables. I suppose it's presented like that so that those following along afterwards don't have to draw out the angles and work out the sizes for themselves. It does tend to imply that it's much more complex than it really is, and that the dimensions have been arrived at by sheer genius or magic. In reality, once you've set the various things that can't be changed, ie the throat diameters, angles and a couple of gaps, the rest almost defines itself. If what I've gleaned is correct, there are a few ratios that need to be adhered to but that's all. I'll probably get egg on my face, but that's how I see it. Using CAD to maintain those ratios as you develop the design eliminates any maths or geometry. You just draw it up and then ask the model what the sizes turned out to be. Years ago these things weren't available to the average ME, but today you can get it all for free.
|
|
|
Post by ettingtonliam on Mar 2, 2019 15:49:20 GMT
I wonder how LBSC arrived at the proportions he did for his injectors which he assured us were reliable. Were they as reliable as he said?
|
|
|
Post by terrier060 on Mar 2, 2019 17:02:07 GMT
YES YES YES they were! Even in a hard water area like Southampton.
|
|
Gary L
Elder Statesman
Posts: 1,208
|
Post by Gary L on Mar 4, 2019 0:57:12 GMT
YES YES YES they were! Even in a hard water area like Southampton. ...but only at the pressures that LBSC used, which I think is 80psi max, plus say 10psi for luck. The late and lamented Ken Swan wrote (in 1970) that LBSC injectors didn't work on his Bridget at the designed 120psi (as other Bridget/Jessie owners will concur). Ken says in his articles that "after much fiddling about, it now works perfectly even with warm water, but the steam cone is .004 in bigger than the specification" I don't think Ken realised back then that the problem lay with the pressure he was using (he jokes about 'thin water' in Surrey!), but later authors like DAG Brown give a similar recipe for dealing with higher boiler pressures. -Gary
|
|
|
Post by Roger on Mar 4, 2019 7:42:38 GMT
YES YES YES they were! Even in a hard water area like Southampton. ...but only at the pressures that LBSC used, which I think is 80psi max, plus say 10psi for luck. The late and lamented Ken Swan wrote (in 1970) that LBSC injectors didn't work on his Bridget at the designed 120psi (as other Bridget/Jessie owners will concur). Ken says in his articles that "after much fiddling about, it now works perfectly even with warm water, but the steam cone is .004 in bigger than the specification" I don't think Ken realised back then that the problem lay with the pressure he was using (he jokes about 'thin water' in Surrey!), but later authors like DAG Brown give a similar recipe for dealing with higher boiler pressures. -Gary Looking at Bob Bramson's book, it would appear that all you have to do is to use a slightly smaller steam cone throat to start with using the same throat diameters for the Mixing and Delivery cones as before. Everything else follows from that, ie the throat of the Condensing cone might need changing slightly to make sure it's still going to work as an Ejector, and that will affect the length of that cone. Bob Bramson gives two columns of figures in Table 2 on page 20 that show the sizes you need for two pressure ranges. Making it work at higher pressure sacrifices it working at quite such a low pressure though, you can't have both.
|
|
|
Post by ettingtonliam on Mar 4, 2019 8:06:06 GMT
Could be a case for having one injector made to work at lower pressure and one for full boiler pressure do you think? Then you are covered for the full range of likely pressures.
|
|
kipford
Statesman
Building a Don Young 5" Gauge Aspinall Class 27
Posts: 566
|
Post by kipford on Mar 4, 2019 8:34:42 GMT
Question: What is the design requirement and the acceptance criteria? Without at least a basic specification that defines the performance requirements nominal and off design, you cannot properly design or test a piece of equipment. Any fluid flow device is at optimum at only one performance point, anything else is off design and performance will be compromised, so the level of compromise and method of validating it needs to be agreed. Starter for 10. Steam inlet pressure and temperature. Tender water volume or mass flow rate and temperature. This to be defined for max, min and nominal conditions. Then with reference to Roger's test thread how is it going to be tested to show that it does what it says in the tin.
|
|
|
Post by Roger on Mar 4, 2019 9:13:14 GMT
Could be a case for having one injector made to work at lower pressure and one for full boiler pressure do you think? Then you are covered for the full range of likely pressures. I think there's a very good case for this, as well as one for having a small and large injector so you can choose how quickly you want the change to take place.
|
|
|
Post by Roger on Mar 4, 2019 9:25:31 GMT
Question: What is the design requirement and the acceptance criteria? Without at least a basic specification that defines the performance requirements nominal and off design, you cannot properly design or test a piece of equipment. Any fluid flow device is at optimum at only one performance point, anything else is off design and performance will be compromised, so the level of compromise and method of validating it needs to be agreed. Starter for 10. Steam inlet pressure and temperature. Tender water volume or mass flow rate and temperature. This to be defined for max, min and nominal conditions. Then with reference to Roger's test thread how is it going to be tested to show that it does what it says in the tin. Agreed, you need to know all of those things, although I'm not sure what relevance the Tender water volume has on the design. Another consideration is whether the layout will affect the design. On 1501, the water feed for the RH injector comes from the underside of the LH tank and goes on a tortuous route to get to the other side. Running a large injector on the RH side might pose problems due to the resistance in that pipe, so a smaller one might make sense on that side. You also have to decide whether hot water is likely to be an issue. To use the scale arrangement fitted to 1501, you have to use water from the side tanks for the injectors. Insulation is going to help, but an injector that works at higher temperatures is preferable. That probably means you need to have a two valve design with a check valve on the overflow too. Finally, you have to decide on whether to use a very small injector in the mix. I quite like the idea of a tiny one used in conjunction with a bigger one, but that's likely to be less reliable for reasons mentioned earlier. A boiler inspector might also decide that the two injectors should be able to cope on their own, and a small one might fall foul of that requirement. That's not an issue if you have an axle pump as the second method of course. Lots of decisions to be made, and no obvious clear path to deciding what those are. At least you can go back and make an injector to a different specification if it doesn't work out the way you planned. A scale injector with a removable cartridge makes that a practical proposition.
|
|
JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,902
|
Post by JonL on Mar 4, 2019 10:51:13 GMT
This is begging to be a popular web-page among model engineers.... enter your boiler pressure and delivery etc, and it pops out a set of dimensions. Get that on Dragons Den!
|
|
|
Post by delaplume on Mar 4, 2019 11:39:52 GMT
Hi Roger,
Quote}----"Finally, you have to decide on whether to use a very small injector in the mix. I quite like the idea of a tiny one used in conjunction with a bigger one, but that's likely to be less reliable for reasons mentioned earlier. A boiler inspector might also decide that the two injectors should be able to cope on their own, and a small one might fall foul of that requirement. That's not an issue if you have an axle pump as the second method of course."
I have the current Boiler test Code 2018 ( Boilers 3 Bar-litres to 1100 Bar litres )..before me and in Section 11...Safety Inspection & Steam Accumulation Test you'll find}----
11.4}--This allows the regulator to be partially opened during the Accumulation Test to allow a small amount of steam to flow through the Superheater for protection....
11.5}--- This calls for inspections to be done as pressure is rising, and then at WP = Working Pressure..
11.6....Correct operation of the following items shall be verified:- a) Boiler water feeding arrangements by at least two independent means ( Hand pump, injectors, mechanical pump, etc. ) b) Water level gauge ---etc c) Water level gauge and pressure gauge clearly visible..
So it all comes down to what is deemed to be the "Correct operation" of an injector ??.........
I would say that}--a) if you have an LP and an HP then the LP is tested within it's stated range and similarly with the HP one... b) Operating correctly simply means that injector is actually putting water into the boiler ...This can be demonstrated usually by the overflow ceasing combined with an eventual dropping of the Boiler Pressure and/or the "Chirping" sound sometimes heard....
Incidentally, if you present 2 injectors and one by-pass pump for test then All 3 must work correctly for obvious reasons.......
Rule 6.5 allows a MINIMUM of two independent means....ie}-- you can have more but they will be subject to test....
I know you are a stickler for originality but if you made the injectors as dummies ie}-- they just carry water through them, then you could use a submersible electric pump within the water tanks powered via a 12v feed from your driving truck.......The water valves will still need to work but visually you could have an exact replica as per 1501....
Just a thought ...
|
|
|
Post by delaplume on Mar 4, 2019 11:51:48 GMT
This is begging to be a popular web-page among model engineers.... enter your boiler pressure and delivery etc, and it pops out a set of dimensions. Get that on Dragons Den! Hi Nobby-------I put "Boiler injector calculator" into Google and this was in amongst the Big Boys stuff}------ modeleng.proboards.com/thread/1076/injector-calculatorWhat goes around, comes around--eventually I suppose ??.......12 years and we're still asking the same questions it seems.... Hey-ho !!
|
|
|
Post by delaplume on Mar 4, 2019 12:05:03 GMT
Hi Roger,
Grab your copy of "Model Steam Locomotive Construction" by Martin Evans and go to page 151 fig 122.....
|
|
|
Post by mutley on Mar 4, 2019 12:39:36 GMT
|
|
baldric
E-xcellent poster
Posts: 208
|
Post by baldric on Mar 4, 2019 13:04:54 GMT
Would you not expect both injectors to work at full pressure, so if either one fails the other can put water in at a sufficient rate to overcome the safety valves? I am saying this not having looked at any regulations or having yet got to a stage where I need to know, just what I would expect. Baldric.
|
|
|
Post by Roger on Mar 4, 2019 13:15:16 GMT
Hi Roger, Grab your copy of "Model Steam Locomotive Construction" by Martin Evans and go to page 151 fig 122..... Hi Alan, It's on a different page in my edition of the book. It's interesting that he doesn't specify the exit diameter of the steam cone, so you can't set the annular regulation from the dimensions. I'm not sure how the Ejector ration works out with that formula he's given. You need to maintain a ratio between the Steam cone throat and the throat of the Condensing cone. It may be that the proportions end up meeting the criteria, but I think I'd rather set that ratio and then adjust the lengths of the Condensing and Mixing cones with that fixed while setting the gap between them to the required size. (whatever that is!) Again, he doesn't seem to be aware of End Regulation either. I wonder if this is something that only Bob Bramson has done?
|
|