Cylinder Drains Question

Discussion in 'TSW General Discussion' started by rennekton#1349, Jun 16, 2022.

  1. rennekton#1349

    rennekton#1349 Well-Known Member

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    Hi Everyone. I purchased the steam route and I had a question regarding the cylinder drains that was brought up in the livestream I was watching. What is the procedure as to when to open and close the drains? Like do we just open them when you are standing still at a station and close when you start departing? Do we open them just before departing or something? Any information would be appreciated since I know nothing about steam trains.
     
  2. solicitr

    solicitr Well-Known Member

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    The cylinder drains are there because when you are standing still at a station, steam still in the cylinders and valve chests tends to condense to water. Water in the cylinders is very, very bad, because unlike steam it's incompressible. Therefore you open the drains, and leave them open until slightly after the train gets moving again (it only takes a half-dozen "chuffs" to blow the water out). Then close them again, because they cost you a lot of power and steam.
     
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  3. meridian#2659

    meridian#2659 Well-Known Member

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    Solicitr explained it. Just wannet to add, in case you have the 3f jinty for tsc. Load the advanced version and try to operate the loco with closed cylinder co-cks. After a while of shunting and stopping you smash the cylinder housing because you cant compress the condensated water. Its modeled really well.
     
  4. JJTimothy

    JJTimothy Well-Known Member

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    You'd start with the cylinder cocks open and close them after the drivers have turned four times- 16 chuffs or 24 on a three cylinder loco'.
     
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  5. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    Good explanations from the crew, I will add a little more information.

    The cylinder castings are big, when they are cooler than the steam, the steam that enters them will condense back to water. Water cannot be compressed. Because it cannot be compressed it will break or bend things when you try.

    Whenever the loco has not been actively steaming for a while you open them because the castings will have started to cool.
    • When you first start off
    • When you've sat in a station for a bit
    • When you've been drifting down hill without using steam
    You need them more in cold weather. A good driver will get into the habit of always opening them when they are coming to a stand or when they are drifting. The other reason to open them when drifting is it reduces the tendency of your cylinders to become giant air pumps.

    Our drivers will often open them periodically when steaming for a few rotations before closing them again to avoid condensate build up when steaming. They also tend to open them when photographers are nearby because it looks good :).

    Many locomotives also have a snifter valve which automatically open when steam chest pressure drops (or if they're like ours open when you boot them) that will have a constant flow of steam through the cylinder casting keeping it warm that helps avoid most condensation.

    Paul
     
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  6. Jonsutt1

    Jonsutt1 Active Member

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    Could you please explain to me at what point in the cycle the piston is compressing the cylinder contents? I thought that once steam has been admitted to a cylinder and pushed the piston as far as it can go (in the process turning the wheels through half a revolution), then during the second half revolution of the wheels, the piston reverses direction and evacuates the used steam from the cylinder via an automatic valve and out through the funnel.

    I would have thought that any condensed steam in the cylinder would also be evacuated by the same route. Does the risk occur because any water in the cylinder being of higher specific gravity than steam just cannot be evacuated fast enough?
     
  7. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    The piston is double acting, so while the steam is pushing on one side, the other side is pushing everything in that cylinder out the exhaust port. Trouble is that port closes just before the inlet opens just before TDC (Top Dead Centre) or the end of travel and that will try to compress anything left in there.

    The inlet and exhaust port for each end of the cylinder are opened and closed (usually) by a single sliding block in the steam chest.

    Paul
     
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  8. gazz292

    gazz292 Well-Known Member

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    yup, and that port closing just before TDC / BDC is done to give a cushion effect, so the piston does not slam all the way forwards/backwards then reverse direction,
    But the air/residual steam trapped acts like a spring.

    but if there's water in there, it can hydraulic and blow the end cap off / cylinders apart.

    They didn't go to all the trouble of adding cylinder cocks and the linkage to operate them just to make pretty steam effects for photographers as the train went past :)
     
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  9. meridian#2659

    meridian#2659 Well-Known Member

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    Thats form a GWR King Class Cut. Take a look at the piston valve (Nr 15 & 16). It has space on the right and left side, currently the steam is going thgrough the front side (left), forcing the connecting Rod 41 into a forward direction movement of the locomotive.
    If you have water inside the chamber, the forces from stress has to go somewhere, and thats usually the weakest parts of that system. Water would basicly have the effect, if you would fill the part in chamber 18 with sand and the wheel tries to make its full revolution while the steam pressure on the opposite side is pushing. What ever peace bursts first, you wont go anywhere anymore after that ;), or at least a noticable loss of steam and pressure would occur.

    1.jpg
     
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  10. roysto25

    roysto25 Well-Known Member

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    Is there an open source for that drawing?
     
  11. Jonsutt1

    Jonsutt1 Active Member

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    Thanks a lot guys. I understand the issue a lot better now.
     
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  12. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    Good to hear and thanks for saying Jonsutt1 always nice to know when we've been helpful.
     
  13. Jonsutt1

    Jonsutt1 Active Member

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    Something I noticed today, if you open the cylinder cocks when going backwards in the 8F, no visible steam is emitted from the cylinders. Is this prototypical, or is it maybe a bug?
     
    Last edited: Jun 21, 2022
  14. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    It is not prototypical.
     
  15. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    Jonsutt1 I just tried opening the drains going backwards
    upload_2022-6-22_17-13-52.png
    and it emits steam.
     
  16. Jonsutt1

    Jonsutt1 Active Member

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    You know I've just tested it and you're absolutely right. I've rerun part of the journey from the other day and sure enough there is visible steam. I must not have had the regulator open wide enough to make it show. Thanks guys.
     
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  17. paul.pavlinovich

    paul.pavlinovich Well-Known Member

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    No worries at all Jonsutt1 glad you can see it.

    I look forward to a future when weather will impact the steam too - in hot weather you shouldn't see it much at all and in cold weather it should hang around everywhere.

    Paul
     
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  18. Jonsutt1

    Jonsutt1 Active Member

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    Yes that would further improve the realism.
     

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