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would this valve design work for a steam engine?

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jonogt:
ya i think its similar to a piston valve.  i couldn't find much info or imagery on them, but what I did seemed pretty close. 

for simplicity, i'm just going to use "on the right" and "on the left" when referencing parts of the valve.  Any use of "top of the stroke" and "bottom of the stroke" are referring to the actual cylinder.

the top series of pictures is looking at it straight from the side... your cylinder would be directly behind it. 

The bottom left picture is looking at it from the front... your eye-level with the flywheel staring down the bore. 

The bottom right picture is looking at it from a birds-eye view... the cylinder would be "above" it (in the picture that is). 

In the bottom pictures, the straight holes (dashed blue) are where the inlet and exhaust hook up, and the ones that are angled go into the cylinder.  I put them at the angles because if they were straight like the holes on the inlets and exhausts side, they would enter the cylinder at different heights of the stroke.  The only way you could have them straight and enter the cylinder at the same stroke height is if the whole valve thing was turned 90 degrees to the cylinder.  The problem I see with this is that now the engine has to move the piston (red) against gravity for half the stroke.  With the setup in my picture, it's just sliding them horizontal. 

A hard part to portray with my limited drawing is that the angled holes are angled on the vertical AND horizontal axis.  The the left holes angle up AND right, and the right holes angle down AND left.  ('left holes' = the left hole on the left set of holes and the left hole on the right set of holes.  same thing for the 'right holes')

As for what goes where, the right hole on the left and the left hole on the right would be inlets, and the left hole on the left and the right hole on the right would be exhausts.  or vice-versa.

The piston (red) would be considerably longer than the manifold (blue), just to ensure a good seal and smooth motion without any hangups edges.  Having the extra length out the front would also ensure that the linkage to the eccentric could just pivot on the piston, rather than needing a pivot point in the middle of the connecting rod.



Does that clear things up decently?

NickG:
Jon,

Just spent a while looking at your drawings and reading you explaination!

I now just about understand it, although I think it's unnecessarily complex  :smart: and would be difficult to machine, it should work, provided you get your dimensions right and you machine it all to close tolerances! You would certainly have something unique if you got it to work!

Getting those angled ports spot on is going to be a nighmare ... as you said, they are angled in both planes!  :doh:  :bang:  :hammer:

Well done for coming up with the design though, it must have taken a lot of thinking :thumbup: Good luck if you try it! 

Nick

jonogt:
Thanks Nick, I actually spent most of the time thinking and starting at diagrams of normal steam chests, and this kind of precipitated out as a side thought.  My drawing may not be fully sufficiently clear, because I actually think this will be simpler to machine than a normal steam chest, but I could be wrong. 

on the angled ports, they will be a hassle but doable I think.  The milling machine i have access to has a colletted drill chuck, so it can easily be used as a super-accurate-versatile-manueverable-heavy-duty drill press, so that is where I will be doing them. 

on the tolerances, I think I can do it.  If I can't get a good enough seal with just the metal, I may try and mimic something like fork seals and piston rings.  The shop has an excellent set of reamers though, so I think I got atleast OK odds that it will work out with just metal-on-metal.


unique/original is something I am kind of going for, so thanks for recognizing its potential there.  I'm pretty sure I'm going to give it a shot, so hopefully it also works  :thumbup:  I turned the cylinder earlier today, and it came out beautiful.  It's about 1.15" outer diameter, 3/4" bore, and about 2.25" deep.  I havn't done the piston yet, but the stroke will probably be about 1.5".  I made it from some 1.25" round brass stock.  The bore reamed well, and it's just buttery smooth.  will post pics of it later.

-Jon

CallMeAl:
Here is a grainy old film clip about a piston type valve from youtube:

jonogt:
Ya I've watched that one before... couldn't get any solid understanding from it.  Does anyone know of another animation or page with good diagrams?  I've searched extensively several times and can barely find anything at all.  What's up with that??  The internet is supposed to have just about everything  :scratch:

On my design, I did think of one part that could be simplified... the angled ports could be angled only on the horizontal axis.  Instead of the inlet and exhaust entering the cylinder one above the other, they would meet and share just one hole (centered vertically and horizontally between them).  At first I thought that this would require an even more perfect seal from the valve components since the ports for inlet and exhaust would be directly connected, but not so much.  In my original design, the only extra buffer is that the steam has to enter the cylinder before trying to escape through the exhaust, which would add maybe one linear inch of flow top ... hardly consequential if my understanding of gas movement is correct. This would make drilling the ports accurately a bit easier, and it would mean matching up 2 larger holes with the cylinder, rather than 4 smaller ones.


Now, I could really really use some advice on choice of materials for this.  I'd like the piston to be around 3/8" diameter and it will need to be about 3" long, and the bore in the manifold will be about 2.5" long.  I'm most likely going to machine the manifold from aluminum because it's readily available in large scrap pieces, but I could sleeve the bore with brass or stainless.  I could turn the piston from aluminum, brass, or stainless.  I read in a different post that 303 SS is nice to machine but 304 sucks, Is that correct?     What do you guys think would be best for each part??


The last thing I got right now is about soldering copper tubing.  I'm planning for it to come from the boiler and then split into 2 at a custom fabricated TEE so that I can have 2 separate pieces of tubing going to the front and rear inlet ports, and the same will go for the exhaust except that it will merge at it's TEE and go to a nice looking chimney/smokestack.  Doing this will require good quality solder joints between copper tubing and brass as well as copper tubing and aluminum.  What type of solder/flux is best for this?  Do I need different kinds for brass and aluminum?  Would I be ok doing the joints with an oxy/acet torch using a real broad bushy flame turned on very low?



Thanks for any help- especially regarding materials and solder,
-Jon

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