baldric
E-xcellent poster
Posts: 208
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Post by baldric on Mar 5, 2019 8:13:09 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. Hi Baldric, No, it doesn't work that way---------Remember that the steam being admitted into the injector is already at the Boiler's OPERATING pressure at that moment in time, and it is in the nature of an injector's design that it's output pressure is always above its' input pressure........and it's this pressure difference that overcomes the CLACK valve and thus inject water....NB}---Clack valves have a very lightweight spring, or in some cases non at all, and it is just the boiler pressure that the feedwater pressure has to overcome...........Because the clack valve area is common to both sides this is not needed in the balance equation... As the incoming water--although hot ---- is of a lower temperature than the steam in the boiler, then some of that steam condenses into water, there is a resultant slight transformation of energy for that process to take place, and the boiler pressure starts to drop as a result.... You may have gathered from this thread so far that you can alter and adjust the various cones to get different outputs...The "Holy Grail" if you like is to get an injector that "Picks up" or starts at a low gauge pressure and continues to operate right up to the WP ( stated Working Pressure ) of the boiler under all operating conditions without "Knocking off" or loosing a lot of water via the overflow... The Boiler Inspector is only required to make sure that all feedwater supply systems actually work ... They get tested up to and including the rated WP..... the quantity of injector output is not required to be tested as such..... I think you last 2 paragraphs agree with part of what I was trying to suggest, that both of the injectors should work at full pressure (full boiler pressure that is or working pressure). I am slightly surprised that "the quantity of injector output is not required to be tested as such" as I would hope that either injector could keep up with the safety valves, may be that expectation of mine is wrong. I will try and follow this thread with interest so I can make mine when the time comes. Baldric.
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Post by Roger on Mar 5, 2019 9:37:49 GMT
Rodger What happens upstream of the steam does have an effect. As you know every time you do work on a fluid, expand it, contract it, turn it etc there is a loss. It is the magnitude of the loss what is important. So to answer Julian's question, there is no correct answer. The aim should always be to minimise the losses. The velocity of the steam in the pipe will determine if a plain entry is Ok or whether a larger pipe contracting down to the nozzle throat diameter is better. With jet pumps we always ran a larger pipe contracting down, but we were dealing with relatively high mass flows and wanted minimise the pressure loss in the system to ensure the entrainment ratio (equivalent to the ratio of the mass flow of water from the tender / mass flow of steam through the nozzle) was as high as possible, typically 10:1 or greater. I need to do some sums to understand what values we are dealing with, I have a hunch the injector entrainment ration is a lot less from the relative sizes of the cones, however being on Holiday precludes this at the moment. I have been thinking about the design a lot and when I get home I intend to go off piste and look at a revised design without recourse to what has gone previously. The second thing is I will investigate doing some computational fluid dynamics (CFD) on a conventional design and what ever I dream up. If the CFD works as I hope (our nickname for it at work was painting by numbers), it will be interesting to see what actually go on inside an injector. This will not be the work of 5 minutes, but I will update if it all goes to plan. Going wine tasting tomorrow in Blenheim😋 Dave Hi Dave, Fair comment, I was being a little cavalier with that suggestion. Of course, if you made the throat a mile long then that would also have an effect. What I was meaning was that Bob Bramson shows just a drilled hole with the the usual drill point angle being all that you need. That might not be the perfect layout, but it would appear that it works. I wonder what the minimum length of throat would be, or if that could be very short?
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Post by Roger on Mar 5, 2019 10:14:45 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. Yes I think so. That is the solution I have adopted anyway. I get the sense that my high pressure injector has a smaller working range than the standard sort, which leaves an inconvenient gap at the low end. It would be nice if the dimensions could be exactly specified for a given max pressure, then you would have the top of the injector's range at your red line, and know that you had the greatest possible range for that particular unit. But that is probably perfection, requiring a degree of accurate manufacture that few of us can aspire to. -Gary Hi Gary, Table 2 on Page 20 of Bob Bramson's book shows the sizes for 20-80PSI and 30-100PSI, so if you need 90 PSI like I do, you can split the difference. It's only the Steam cone throat that changes. The implication is that you may be able to go further up the pressure range by reducing the Steam cone throat even more. Of coarse, there is a knock on effect on the ejector part of the design as you change these sizes, the Condensing cone throat size would need to be reduced too, and that affects the length of the cones if you keep the gap between the Condensing and Mixing cones the same. The problem with the current prescriptive way of making injectors is that you're given a finished set of sizes as the completed item in most cases. There are some formulae that give the ratio of various diameters and lengths, but I'm suspicious of them. That's because when you draw this in CAD and set constraints to maintain cones that truly line up with each other, I'd be surprised if those formulae hold true. If you take the diameters and angles as being correct, there's very little that you can change. The start and end locations of the Condensing and Mixing cones have to all lie on that 9 degree taper cone. The Ejector design fixes the position of the Condensing cone on that, and the throat diameter of the Mixing cone from the table decides its position. When you decide the gap between the cones, that fixes the length of the Mixing cone. There's not much left that you can change! The length of the Condensing cone is variable, but the distance to the throat on the delivery cone isn't. The amount of bell mouth entry to the Delivery cone is variable though. The End regulation distance is fixed, although I'm not certain how to arrive at that yet. So my conclusion is that if Bob Bramson is right, you can't change all that much if you're to maintain an efficient ejector as well as meeting the other throat size constraints. The reference designs in D.A.G Brown's books show dimensions that don't appear to follow any strict rules or proportions. If you try to find relationships between the various dimensions across the range of sizes, there don't appear to be any. I get the impression they have all been arrived at though trial and error.
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Post by terrier060 on Mar 5, 2019 15:15:03 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 Quite correct Gary - our normal working pressures on 5" and 3.5" gauge ranged between 75 and 90psi.
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kipford
Statesman
Building a Don Young 5" Gauge Aspinall Class 27
Posts: 566
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Post by kipford on Mar 5, 2019 18:31:44 GMT
Roger Sorry, misunderstood your original point. Theoretically you want a knife edge if contracting, but that is impossible to maintain in a production environment. So we used to use a 1.0/0.5 mm parallel section instead. Dave
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Mar 6, 2019 0:44:03 GMT
Yes I think so. That is the solution I have adopted anyway. I get the sense that my high pressure injector has a smaller working range than the standard sort, which leaves an inconvenient gap at the low end. It would be nice if the dimensions could be exactly specified for a given max pressure, then you would have the top of the injector's range at your red line, and know that you had the greatest possible range for that particular unit. But that is probably perfection, requiring a degree of accurate manufacture that few of us can aspire to. -Gary Hi Gary, Table 2 on Page 20 of Bob Bramson's book shows the sizes for 20-80PSI and 30-100PSI, so if you need 90 PSI like I do, you can split the difference. It's only the Steam cone throat that changes. The implication is that you may be able to go further up the pressure range by reducing the Steam cone throat even more. Of coarse, there is a knock on effect on the ejector part of the design as you change these sizes, the Condensing cone throat size would need to be reduced too, and that affects the length of the cones if you keep the gap between the Condensing and Mixing cones the same. The problem with the current prescriptive way of making injectors is that you're given a finished set of sizes as the completed item in most cases. There are some formulae that give the ratio of various diameters and lengths, but I'm suspicious of them. That's because when you draw this in CAD and set constraints to maintain cones that truly line up with each other, I'd be surprised if those formulae hold true. If you take the diameters and angles as being correct, there's very little that you can change. The start and end locations of the Condensing and Mixing cones have to all lie on that 9 degree taper cone. The Ejector design fixes the position of the Condensing cone on that, and the throat diameter of the Mixing cone from the table decides its position. When you decide the gap between the cones, that fixes the length of the Mixing cone. There's not much left that you can change! The length of the Condensing cone is variable, but the distance to the throat on the delivery cone isn't. The amount of bell mouth entry to the Delivery cone is variable though. The End regulation distance is fixed, although I'm not certain how to arrive at that yet. So my conclusion is that if Bob Bramson is right, you can't change all that much if you're to maintain an efficient ejector as well as meeting the other throat size constraints. The reference designs in D.A.G Brown's books show dimensions that don't appear to follow any strict rules or proportions. If you try to find relationships between the various dimensions across the range of sizes, there don't appear to be any. I get the impression they have all been arrived at though trial and error. I'm sure that's right Roger, and I mean no slight on Bramson or Brown. Also, when most of the trial and error was taking place, there is the issue of measuring and reporting to consider. So you make an injector, with discrete cone sizes. You can't make and test every possible size/angle, so you find a combination that works adequately, though you can't be sure it is optimal, nor even which side of optimal it might be. You then have to accurately measure what you have actually made, as distinct from what you set out to make... Nowadays Model Engineers can afford tooling and measuring equipment capable of accuracy and repeatability that LBSC would not have believed, but measuring tiny internal diameters and angles still has many pitfalls (or it does here!) -Gary
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Post by Roger on Mar 6, 2019 8:09:00 GMT
Hi Gary, Table 2 on Page 20 of Bob Bramson's book shows the sizes for 20-80PSI and 30-100PSI, so if you need 90 PSI like I do, you can split the difference. It's only the Steam cone throat that changes. The implication is that you may be able to go further up the pressure range by reducing the Steam cone throat even more. Of coarse, there is a knock on effect on the ejector part of the design as you change these sizes, the Condensing cone throat size would need to be reduced too, and that affects the length of the cones if you keep the gap between the Condensing and Mixing cones the same. The problem with the current prescriptive way of making injectors is that you're given a finished set of sizes as the completed item in most cases. There are some formulae that give the ratio of various diameters and lengths, but I'm suspicious of them. That's because when you draw this in CAD and set constraints to maintain cones that truly line up with each other, I'd be surprised if those formulae hold true. If you take the diameters and angles as being correct, there's very little that you can change. The start and end locations of the Condensing and Mixing cones have to all lie on that 9 degree taper cone. The Ejector design fixes the position of the Condensing cone on that, and the throat diameter of the Mixing cone from the table decides its position. When you decide the gap between the cones, that fixes the length of the Mixing cone. There's not much left that you can change! The length of the Condensing cone is variable, but the distance to the throat on the delivery cone isn't. The amount of bell mouth entry to the Delivery cone is variable though. The End regulation distance is fixed, although I'm not certain how to arrive at that yet. So my conclusion is that if Bob Bramson is right, you can't change all that much if you're to maintain an efficient ejector as well as meeting the other throat size constraints. The reference designs in D.A.G Brown's books show dimensions that don't appear to follow any strict rules or proportions. If you try to find relationships between the various dimensions across the range of sizes, there don't appear to be any. I get the impression they have all been arrived at though trial and error. I'm sure that's right Roger, and I mean no slight on Bramson or Brown. Also, when most of the trial and error was taking place, there is the issue of measuring and reporting to consider. So you make an injector, with discrete cone sizes. You can't make and test every possible size/angle, so you find a combination that works adequately, though you can't be sure it is optimal, nor even which side of optimal it might be. You then have to accurately measure what you have actually made, as distinct from what you set out to make... Nowadays Model Engineers can afford tooling and measuring equipment capable of accuracy and repeatability that LBSC would not have believed, but measuring tiny internal diameters and angles still has many pitfalls (or it does here!) -Gary Hi Gary, I suspect this is why Bob Bramson wrote his book of explanation rather than delivering completed designs. It's just a pity that it's not more clearly written and doesn't contain a worked example from end to end, explaining the reasons for the decisions made. I imagine he thought he'd done enough to make the process clear and that an example wasn't necessary. Not so. You're absolutely right about measuring angles and diameters without specialised equipment. I doubt if the angles of home made reamers is that accurate either. This is one area I'm fortunate in having the Jones & Shipman tool and cutter grinder with an accurate angle measuring system I made years ago for grinding collet tapers. Even then, getting the precise diameters at a given point in the cones is far from easy.
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robmort
Hi-poster
3.5" Duchess, finishing 2.5" gauge A3 and building 3.5" King
Posts: 172
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Post by robmort on Mar 9, 2019 17:09:26 GMT
Roger, just came across this fascinating thread. I had a brief email conversation with Bob Bramson 2 years ago when I was building my injectors. I also found his articles rather confusing and he kindly clarified a few points in them. Pity he's not reading this thread. Going back to the Combining cone lengths, the relative length of the Condensing (L1) to the overall cone (Lm) is stated in Martin Evans book as 2/5 while a value based on Bramson's dimensions has been given as L1=0.44*(Lm-gap/2). Obviously these are only a guide. My main interest is in smaller 4oz/min injectors which I covered here: modeleng.proboards.com/thread/11763/micro-injectorThe main difficulty I found in making them was in drilling the tiny nozzles so that they started and remained accurately on-axis as the drill bit went to full depth. For tiny bits the end angles are hard to grind well and the drilling technique has to be precise. Rob
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Post by Roger on Mar 9, 2019 17:59:46 GMT
Roger, just came across this fascinating thread. I had a brief email conversation with Bob Bramson 2 years ago when I was building my injectors. I also found his articles rather confusing and he kindly clarified a few points in them. Pity he's not reading this thread. Going back to the Combining cone lengths, the relative length of the Condensing (L1) to the overall cone (Lm) is stated in Martin Evans book as 2/5 while a value based on Bramson's dimensions has been given as L1=0.44*(Lm-gap/2). Obviously these are only a guide. My main interest is in smaller 4oz/min injectors which I covered here: modeleng.proboards.com/thread/11763/micro-injectorThe main difficulty I found in making them was in drilling the tiny nozzles so that they started and remained accurately on-axis as the drill bit went to full depth. For tiny bits the end angles are hard to grind well and the drilling technique has to be precise. Rob Hi Rob, Maybe someone will alert Bob and he might be willing to contribute. I tried to reach him last year through the club that publishes the book, but got no reply. I didn't even know he was still alive. What I'd really like to know is the reason for the proportions of the Condensing and Mixing cone lengths because there seems to be a universal agreement on the kind of proportions but no explanation as to what happens if you change them. From Bobs' book, there seems to be little leeway on the Mixing cone for reasons I've explained a couple of times before, so it's only the length of the Condensing cone that's in question. I'd just like to know what happens if you make that much shorter and much longer, because basically there's nothing in the geometry that says you can't have that any length you like while still meeting all of the other throat and gap dimensions. I too am interested in the smaller injectors, I can't see why those can't be reliable. Personally, I'd avoid using HSS drills in these small sizes, they are way to flexible in my opinion. I think you're much better off using PCB drills, but you will have to make sure the tailstock it properly aligned and the drill chuck is on the centre line. It might be worth making a special precision adaptor that takes 1/8" shanks which is what all of those sizes use. Forget trying to sharpen tiny drills, just buy new ones, they're so cheap as to not be worth messing about with and they're ground better than you could ever hope to achieve. These drills are routinely made to 70microns (2-3/4 thou!) in diameter these days! It also makes me wonder if the two cones should be reamed in the same operation, with a mark on the cone to show which way they were aligned when machined so they could be assembled in that orientation. Super precision bearings made to the finest tolerances and sold as matched pairs to exactly this, to minimise runout, and I'd wager they're made to much better tolerances than anything we do.
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Post by mutley on Mar 9, 2019 20:18:47 GMT
Not so sure about that Roger! I've never seen or tried a Bob Bramson injector, and neither have you! I can tell you that the Linden injectors of the 1940s early 50s work extremely well, as do the Arthur Grimmett injectors of the late 50s to circa 1980, as do all the Chiverton Injectors because I have used them and tested them and played about with them. Arthur Grimmett always told me he made over 3,000 injectors for Reeves and Kennions. How many has Bob made? I have so far not heard of anyone having a Bob Bramsom injector on this forum stating "Yes, I've got one, or I made one, and it it is so wonderful and perfect and utterly reliable"! (If you were to ask Kipford should the steam cone have a converging taper entrance before the throat as opposed to a simple drilled hole, then we might make things clearer in respect of the steam cone). Cheers, Julian Ive got one...In fact Ive got a high pressure (200psi) and a low (150psi) version for my steam roller. I'm not 100% happy with either and I don't believe Bob supplies injectors any more! My only comment would be stay to stay away from moving cones, the slightest bit of dirt is enough to stop them functioning.
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Post by Roger on Mar 9, 2019 20:48:29 GMT
Not so sure about that Roger! I've never seen or tried a Bob Bramson injector, and neither have you! I can tell you that the Linden injectors of the 1940s early 50s work extremely well, as do the Arthur Grimmett injectors of the late 50s to circa 1980, as do all the Chiverton Injectors because I have used them and tested them and played about with them. Arthur Grimmett always told me he made over 3,000 injectors for Reeves and Kennions. How many has Bob made? I have so far not heard of anyone having a Bob Bramsom injector on this forum stating "Yes, I've got one, or I made one, and it it is so wonderful and perfect and utterly reliable"! (If you were to ask Kipford should the steam cone have a converging taper entrance before the throat as opposed to a simple drilled hole, then we might make things clearer in respect of the steam cone). Cheers, Julian Ive got one...In fact Ive got a high pressure (200psi) and a low (150psi) version for my steam roller. I'm not 100% happy with either and I don't believe Bob supplies injectors any more! My only comment would be stay to stay away from moving cones, the slightest bit of dirt is enough to stop them functioning. Hi Mutley, That's interesting, I wasn't aware that Bob made them commercially. In fairness to anyone, a sample of two can't be taken as an indictment of a person's output, especially when these are not in the normal range of ones we would normally see on the average model. You don't say what the issues are, so it's hard to draw any conclusions from what you say. What size are the injectors you have? I don't believe there's been any mention of 'moving cones'. Perhaps you could explain what you mean by that? Do you mean that they move during operation?
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Post by delaplume on Mar 9, 2019 22:05:20 GMT
Hi Roger,
Moving cone Injectors ??..........10 a' penny, Sir !!
Black Book........fig 25.
The combining cone is in 2 parts}-- fixed and moving, the general idea is similar to the hinged flap on a combining cone ie}---it will knock off when air passes through then automatically re-start when the flow of water-only has been re-established.........You can actually hear it "thwack" sometimes........Naturally it (the moving cone ) is subject to wear or jamming as mentioned...
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Post by Roger on Mar 10, 2019 7:49:22 GMT
Hi Roger, Moving cone Injectors ??..........10 a' penny, Sir !! Black Book........fig 25. The combining cone is in 2 parts}-- fixed and moving, the general idea is similar to the hinged flap on a combining cone ie}---it will knock off when air passes through then automatically re-start when the flow of water-only has been re-established.........You can actually hear it "thwack" sometimes........Naturally it (the moving cone ) is subject to wear or jamming as mentioned... Hi Alan, I've seen that in full size, but we're talking about miniature injectors...
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Post by mutley on Mar 11, 2019 22:29:09 GMT
Too late now but I will take the smaller injector apart and produce some pictures for you to explain.
The larger injector is 8 pints/min and I spent a fair amount of time tweaking it to get the performance I wanted/expected from it. From memory I reduced the OD of the nose of the steam cone to increase water flow and placed a 12thou shim under neath it to also increase the working pressure. The ball in the overflow was restrictive as was the overflow passage way which was just a drilled hole. The ball has gone and the passage is now substantially larger. Finally the ball in the clack ended up with 196thou of lift to allow the water to flow, not an injector issue as such but still needed to get the correct performance. I personally know off other people with these injectors who have had trouble with them because they have all asked me how I got mine working and what I did to get it working...
I don't know how many Bob made but it was a reasonable size batch. He has been the only person to make high pressure, model sized, injectors which would work up to 200psi and there is still as big hole in the market for injectors in this pressure range to suite the smaller half size tractions engines or those with the higher pressure boilers to aid compounding.
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robmort
Hi-poster
3.5" Duchess, finishing 2.5" gauge A3 and building 3.5" King
Posts: 172
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Post by robmort on Mar 20, 2019 21:42:54 GMT
..... What I'd really like to know is the reason for the proportions of the Condensing and Mixing cone lengths because there seems to be a universal agreement on the kind of proportions but no explanation as to what happens if you change them. From Bobs' book, there seems to be little leeway on the Mixing cone for reasons I've explained a couple of times before, so it's only the length of the Condensing cone that's in question. I'd just like to know what happens if you make that much shorter and much longer, because basically there's nothing in the geometry that says you can't have that any length you like while still meeting all of the other throat and gap dimensions. That would be interesting but most likely, as usual, there are very few measurements of this type of thing and it's based on rule of thumb. Definitely the two parts of the mixing cone are reamed in one operation before parting them, or better still leaving them as one piece, as I've done and which has been done before and described by Ted Crawford etc.. see below
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Post by Roger on Mar 20, 2019 21:58:20 GMT
Too late now but I will take the smaller injector apart and produce some pictures for you to explain. The larger injector is 8 pints/min and I spent a fair amount of time tweaking it to get the performance I wanted/expected from it. From memory I reduced the OD of the nose of the steam cone to increase water flow and placed a 12thou shim under neath it to also increase the working pressure. The ball in the overflow was restrictive as was the overflow passage way which was just a drilled hole. The ball has gone and the passage is now substantially larger. Finally the ball in the clack ended up with 196thou of lift to allow the water to flow, not an injector issue as such but still needed to get the correct performance. I personally know off other people with these injectors who have had trouble with them because they have all asked me how I got mine working and what I did to get it working... I don't know how many Bob made but it was a reasonable size batch. He has been the only person to make high pressure, model sized, injectors which would work up to 200psi and there is still as big hole in the market for injectors in this pressure range to suite the smaller half size tractions engines or those with the higher pressure boilers to aid compounding. Sorry for the slow response to this, I replied but I think it failed to get submitted for some reason. Finger trouble I shouldn't wonder! That sounds like a really large injector, and 12thou seems like an enormous adjustment. The ball valve in the overflow is to stop air being sucked into the boiler, something I would have thought you would want to avoid if you have a Steel boiler? Maybe finding a way to reduce the restriction would be a better solution than removing the ball? If it's not a scale item, that might be possible. It would appear that not enough development was done on these from what you say.
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Post by Roger on Mar 20, 2019 22:08:44 GMT
..... What I'd really like to know is the reason for the proportions of the Condensing and Mixing cone lengths because there seems to be a universal agreement on the kind of proportions but no explanation as to what happens if you change them. From Bobs' book, there seems to be little leeway on the Mixing cone for reasons I've explained a couple of times before, so it's only the length of the Condensing cone that's in question. I'd just like to know what happens if you make that much shorter and much longer, because basically there's nothing in the geometry that says you can't have that any length you like while still meeting all of the other throat and gap dimensions. That would be interesting but most likely, as usual, there are very few measurements of this type of thing and it's based on rule of thumb. Definitely the two parts of the mixing cone are reamed in one operation before parting them, or better still leaving them as one piece, as I've done and which has been done before and described by Ted Crawford etc.. see below
I really like the idea of keeping the two halves of the combining cone together, it's certainly the most accurate way to get the taper perfectly aligned. Of course, you can't put the magic chamfer on the entry to the Mixing cone part, but with it perfectly aligned you almost certainly don't need it anyway. We know that the column of water reduces slightly as it exits the Condensing cone. I'd like to suggest that the positioning of these two cones relative to each other is the single most important area where accuracy is key. Yes, it all needs to be accurately made, but there's a little more room for error on the other alignments in my opinion. If you look at how it's normally done with separate cones, the precise length of the body is vital to getting the gap right, as is the precise length of the two insertion tools. That's three things with a tolerance to achieve the same thing as the single piece one you've pictured. The slot becomes a bit of a challenge when the size of the injector is small though, but there are slitting saws that will do the job. I'm curious about the parallel section at the RH end of the Mixing cone. I was under the impression that the taper should end precisely at the end of the cone. Having said that, it may well be that the column of water contracts at that point so it makes little difference. Maybe a fluid dynamics expert could comment on that?
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robmort
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3.5" Duchess, finishing 2.5" gauge A3 and building 3.5" King
Posts: 172
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Post by robmort on Mar 20, 2019 22:21:05 GMT
Of course the other, usual, way of doing it is to have separate cones (with a suitable spacer perhaps) but do the final reaming cut when they are in place.
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Post by Roger on Mar 20, 2019 23:00:56 GMT
Of course the other, usual, way of doing it is to have separate cones (with a suitable spacer perhaps) but do the final reaming cut when they are in place. I think D.A.G Brown says to give the reamer a final twist when the cones are in place, but that seems like an admission that the method simply isn't good enough. How much is a final twist, and how will you know what the final size is? Perhaps this is known from the distance the reamer it entered into the cone, but I suspect it's just done by feel. Why is this being done? Presumably because the cones are the wrong distance apart or they don't line up, else it wouldn't be necessary. Clearly these methods work, but it doesn't smack of the Precision Engineering that we're repeatedly told we need. To my mind the method should aim to produce the whole assembly as closely as possible to the drawing. Another thing worth noting is that the cones are all pretty short, and that means there's more chance of them sitting at an angle. With a one piece cone, that length is more than double, and the correct alignment of the whole cone is more easily achieved. I can see a lot of merit in making this in one piece.
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,902
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Post by JonL on Mar 21, 2019 6:58:31 GMT
It's one of those things that is actually so simple and obvious you wonder why you didn't think of it earlier, but yes it makes perfect sense for a few reasons.
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