It will not run.....

Discussion in 'A Work In Progress' started by Jmccrack, Jul 20, 2018.

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  1. Jul 20, 2018 #1

    Jmccrack

    Jmccrack

    Jmccrack

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    upload_2018-7-19_16-43-28.jpeg

    upload_2018-7-19_16-44-16.jpeg

    upload_2018-7-19_16-44-46.jpeg

    Help guys this is not rocket surgery! It will almost start but not quite. It should be simple. One side at TDC steam valve let’s steam into the top of that chamber drives the piston down . The other side BDC the steam valve let’s steam into the bottom of that chamber and drives the piston up. I even made 2 polycarbonate top covers so I can see the valve action. When I put air in the system the 2 cylinders seem to be fighting each other. Any help would be appreciated. BTW before I painted it I had it running like a charm. And each side runs well on its own.
     
  2. Jul 20, 2018 #2

    XD351

    XD351

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    Is the valve sealing ? If you are getting admission into both ends of the cylinder at the same time i would suggest the valve is not sealing or there is a problem with the casting ? Maybe a blowhole connecting both ports ? Maybe the valve is not long enough , you want one port just closed as the other just opens .
    Looking at the top photo you have the crank set at 180 deg apart but it looks like the eccentrics are not set 180 apart to each other.
    Try to set one cylinder up and get that running ( it will turn the dead cylinder over no problems then once you have one working just copy what you did on the other .
    At bdc you want the port closest to the crank just opening and the the port closest to the head just closed , you change the valve timing by moving the eccentric position on the crank and you change the valve position by adjusting the valve position on the valve rod .
    Keith appleton made a video of setting the valve timing on a steam engine and you can view it on his youtube channel.
    HTH !
    Ian .
     
    Last edited: Jul 20, 2018
  3. Jul 20, 2018 #3

    Jmccrack

    Jmccrack

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    I can get one or the other running just fine. When I pipe them together no joy. I just came back from the shop and I got them to run together but very rough.m
     
  4. Jul 20, 2018 #4

    rlukens

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    I can't prove this without thinking way to hard, but I suspect if you'll change the "timing" between A and B to something less than 180, things will happen. Give it a shot.
     
  5. Jul 20, 2018 #5

    XD351

    XD351

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    I'm surprised that the crank is of 180 degree design , the few twins i have made are all 90 degree cranks so they self start .
    If you can get each side running separately and smoothly ( and both in the same direction ) it should run but to get each side running by itself you would have to disconnect the supply manifold so maybe the issue lies there ?
    If the valve timing is out by even a small amount the cylinders will fight each other and it won't run or at best will run very roughly .
     
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  6. Jul 20, 2018 #6

    Jasonb

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    Looking at the top picture your cranks are 180degrees apart but the levers actuated by the valve rods are in the same position, I would expect them to be either side of vertical so steam goes into one end of first cylinder and opposite end of the second.

    Are the two grub screws that can be seen in the brass either side of the flywheel hub holding the eccentrics, if so that confirms you have timing issues
     
    Last edited: Jul 20, 2018
  7. Jul 20, 2018 #7

    XD351

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    What would be the ultimate is some video of the engine being turned over by hand and showing the valve operation .
     
  8. Jul 20, 2018 #8

    spacy

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    I agree with Jasonb looks like the eccentrics are set the same(ish) so the engines will try to run in opposite directions, best to set each engine individually at TDC with a 90 degree lag whilst rotating the flywheel the same way that way you can be sure they are both going the same way.
     
  9. Jul 20, 2018 #9

    dkwflight

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    Hi
    I have to say the crank timing is a bit off.
    Set the crank to 90 degrees from each other and start over
    Dennis.
     
  10. Jul 20, 2018 #10

    oldboatguy

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    Hello,

    You have two double acting steam cylinders which are coupled at 180 degrees apart. What you should do is couple them 90 degrees apart that way you will have a power stroke every 90 degrees and no possibility of a dead center. When you couple them at 180, your timing must be absolutely perfect, the humidity must be right, and the moon must be in the right phase in order for them to actually run and not inadvertently oppose each other. I think Robert Lewis Stephenson learned this back in the 1830's in designing steam locomotives. That 90 degree offset was used from then on until steam was replaced by diesel.
    Tandem marine engines were also set at 90 degrees. Triple expansion ones were at 120 degrees so that there was always a power stroke going on all the way around the circle.

    Hope this helps,
    Oldboatguy
     
  11. Jul 20, 2018 #11

    Jmccrack

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    Guys.THANKYOU!! I had no idea. When you look at the drawing I have clearly the cylinders are running at 180 deg not 90. What you are all saying makes so much sense. So back to the shop. I will take the main shaft out and cut a flat at 90 deg. So I can adjust the counter weight at 90 deg to each other not 180. Again thanks. This is my first 2 cylinder.
     
  12. Jul 20, 2018 #12

    Jmccrack

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    I just have to say again this forum is great for help like that. “ It takes a village”
     
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  13. Jul 20, 2018 #13

    johwen

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    Hello,
    I would think the timing of the valve eccentrics are out of phase they should be set 180 degrees apart also. Cheers. john
     
  14. Jul 21, 2018 #14

    Charles Lamont

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    It is hard to tell from the photos how you have made provision for the valves to float vertically on their spindles to allow them to seal against the port-faces.
     
  15. Jul 21, 2018 #15

    karolh

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    Even though I'm not skilled in the art of miniature machining I do enjoy seeing what you guys can make from chunks of metal....a great site to visit with wonderful pieces on show.
     
  16. Aug 3, 2018 #16

    Jmccrack

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    Hey guys still no joy. I was wondering I followed these plans to the letter. How much wider should the slide valve be than the
    2 outside edges of the power ports? Right now my slide valve is .551” wide. And outside to out side on my ports is .531”. That’s only .010” per side. Is it possible that when the slide valve moves at one point both ports are open allowing air into both side of the cylinder?

    upload_2018-8-2_16-12-7.jpeg
     
  17. Aug 3, 2018 #17

    Jasonb

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    It is difficult to say as the engine may have been designed with little or no lap but what I would say from looking at the photo and comparing the length of the 3 slots with the cavity in the valve is that you have the valve rotated 90degrees, or it is a lot wider than needed. I have seen this done several times

    Can you post a bit of the drawing that shows the port faces and the valve to confirm this.
     
  18. Aug 3, 2018 #18

    Lofty76

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    Hi Jm,

    Difficult to see from a photo but it looks as if the slide valve is screwed directly to the valve rod, this would make it almost impossible for the valve to seat against the vlave face.

    Normally the valve is free to float and is held against the valve face by steam pressure, no matter how good your machining is, its very unlikely that the valve could seat properly as shown in the photos.

    Can we see the drawing arrangement for the valve chests etc?

    Best regards

    Lofty
     
  19. Aug 3, 2018 #19

    Jim McDonald

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    I think your cranks need to be at 90 degrees, you have them at 180 degrees. Just a thought
     
  20. Aug 3, 2018 #20

    Jasonb

    Jasonb

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    Forget that I just looked on Grabcad.

    The cavity in the valve is 8mm, exhaust port 3mm and 2mm of metal between giving a total of 7mm. So when the valve is in the mid position air/steam will pass straight from the inlets to the exhaust. Not what you want

    Its an unusual valve port arrangement as the central exhaust port is usually double the size of the inlets or maybe a bit less so would expect 5-6mm

    Also agree that there is no provision for the valve to find its own position on teh portface or lift off to avoid hydraulic lock

    Drawing downloads from here
    https://grabcad.com/library/dual-horizontal-steam-engine-in-factory-layout-1
     

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