Why can't this stuff be easier?
No new pictures or fun stuff today I'm afraid,. All the bodywork is in the paint shop ( or as most people call it.... "the kitchen") so I haven't got anything new to show. But today's mental hernia comes thanks to Mr F, who has re assembled the valve gear, but at this stage we are still trying to work through the "issues" that beloved winsons left us.
Obviously the first major issue was the valve exhaust cavity, not a difficult issue to fix. The origanal valve had a cavity of .5" where it should have been .374" calculated from .25" exhaust port and adding 2x .062" wich is the land either side. This means now both steam ports are shut, untill the valve moves either way, realising one end of the cylinder to exhaust, we don't rele have to worry about things like exhaust lap as we aren't talking major volumes of steam and with such small cylinders, and generally everything being small time isn't a major factor so events happen almos instantly.
Haveing got the valve gear back in the loco, with all the small mods to make it work we are at the point where we can "see what happens".
So armed with all sorts of mesuring tools we start by working out the valve movement, ( in this case .381") so half the travel gives us .1905" either side. Basicly it means that at some point near the end of piston stroke the valve will be in its "centre" possition, so both steam ports shut to exhaust. The valve then moves .1905" in one direction to open a steam port to exhaust and the other end to steam. It then moves back to the center somewhere near end of piston stoke the other end of the cylinder then moves the same distance in the other direction, to push the piston back the other way, or at least that's the theory!! So we know the valve will travel .1905" in either direction, so far it's still fairly simple..
Now for the harder part
The most frustrating thing about winsons was they send out with each kit a set of instructions and drawings, unfortunatly they are only GA (general arrangement) so they are basicly pretty pictures to show how it fits together. This is great if your building an air fix kit, Not so useful when building locos! There is no given or stated dimentions for anything, at all! Possably so no one could work out how much of the kits were wildly inaccurate!!
This gives us a problem, We don't know how well or badly the valve gear was designed, We can only assume that it was desinged by someone who half knew what they were doing. The big issue is we dont know how much lap and lead it was supposed to have, all we know is the old vlaves were wrong. But how wrong? It may have been just a case of the exhaust port was almost .13" too long. It could be the exhaust port plus any manner of other things, so at this point we just dont know, and withough takeing the entire thing to bits and mesureing everything to try and get some idea of the lengths/ radius's of everything and then back working it thought a simulator we have no way of knowing. So we have come up with a plan to make the valves much longer than they should be, infact in full gear (giveing us most travel possable,) the valve should only open the steam port by .01". This was fairly simple to work out, the length of the valve faces from the outside steam port across the exhaust to the oustide of the other steam port is .624" add the total vale travel gives us 1.005". if we left it here it wouldnt open either steam valves either end but the valve line would be on the outter port line, so we then take off .01" a side, this means the ports will open by .01" a side so the valve ends up being .985". This is useful at this stage because we can put the valve bang in the middle as we know there will be .01" at most between the valve and port, also it means we can measure the valve movement and then we can adjust the eccentric Rods lengths to give us equal movement forwards and backwards, this means we can get everything set apart from the valve itself. Obviously .01" isn't enough steam input to make it work, so now we have to come to a size for the valve ...... Errrm, well this is now down to educated guess work!!! The valve requires enough length to cover the steam ports + some lap or it would be opening the ports far far too early, so to make it "work" and to open the steam port fully the valve would be as big as the travel - the steam ports, so in this case it would be, .0655" lap at both ends, then .125" solid material that covers the valve ports, and finally .374"exhaust port, add all that up and the valve becomes .755" long, but wait! Before you think that's it, when you bring the "lead" into the equation, you will find that it would be opening the ports early still, also there is no need to open the steam port 100% to live steam. So let's add some more lap. If we set ourself to only opening the steam port 3/4 of its travel, we just need to add that extra quarter to the valve, so the port is .125" so decide by 4 equals, .03125". Now add that to both ends of the valve. And the new length is .8175", close enough?...... The theory makes sense, but in practice who knows?! Suck it and see I guess!
Well this while bit may seem like a lot of pointless reading but there is method to it. It's given me a while to put my thoughts down out of my head so I can work through how it should work and how to arrive at where we need to be. Also for anyone having a skim through you may gleam a small incite into how these things work, and most of all, it will give James something to read and work through, being a up and coming engineer and needing a little hand with the maths side, I hope I have outline it all in a way he can understand and get to grips with, so once you have had a read give me a shout and tell me if you understand it!
Anyways, I suppose I had better do some work today, .....maybe!
Rock n roll!!!
This gives us a problem, We don't know how well or badly the valve gear was designed, We can only assume that it was desinged by someone who half knew what they were doing. The big issue is we dont know how much lap and lead it was supposed to have, all we know is the old vlaves were wrong. But how wrong? It may have been just a case of the exhaust port was almost .13" too long. It could be the exhaust port plus any manner of other things, so at this point we just dont know, and withough takeing the entire thing to bits and mesureing everything to try and get some idea of the lengths/ radius's of everything and then back working it thought a simulator we have no way of knowing. So we have come up with a plan to make the valves much longer than they should be, infact in full gear (giveing us most travel possable,) the valve should only open the steam port by .01". This was fairly simple to work out, the length of the valve faces from the outside steam port across the exhaust to the oustide of the other steam port is .624" add the total vale travel gives us 1.005". if we left it here it wouldnt open either steam valves either end but the valve line would be on the outter port line, so we then take off .01" a side, this means the ports will open by .01" a side so the valve ends up being .985". This is useful at this stage because we can put the valve bang in the middle as we know there will be .01" at most between the valve and port, also it means we can measure the valve movement and then we can adjust the eccentric Rods lengths to give us equal movement forwards and backwards, this means we can get everything set apart from the valve itself. Obviously .01" isn't enough steam input to make it work, so now we have to come to a size for the valve ...... Errrm, well this is now down to educated guess work!!! The valve requires enough length to cover the steam ports + some lap or it would be opening the ports far far too early, so to make it "work" and to open the steam port fully the valve would be as big as the travel - the steam ports, so in this case it would be, .0655" lap at both ends, then .125" solid material that covers the valve ports, and finally .374"exhaust port, add all that up and the valve becomes .755" long, but wait! Before you think that's it, when you bring the "lead" into the equation, you will find that it would be opening the ports early still, also there is no need to open the steam port 100% to live steam. So let's add some more lap. If we set ourself to only opening the steam port 3/4 of its travel, we just need to add that extra quarter to the valve, so the port is .125" so decide by 4 equals, .03125". Now add that to both ends of the valve. And the new length is .8175", close enough?...... The theory makes sense, but in practice who knows?! Suck it and see I guess!
Well this while bit may seem like a lot of pointless reading but there is method to it. It's given me a while to put my thoughts down out of my head so I can work through how it should work and how to arrive at where we need to be. Also for anyone having a skim through you may gleam a small incite into how these things work, and most of all, it will give James something to read and work through, being a up and coming engineer and needing a little hand with the maths side, I hope I have outline it all in a way he can understand and get to grips with, so once you have had a read give me a shout and tell me if you understand it!
Anyways, I suppose I had better do some work today, .....maybe!
Rock n roll!!!
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