Looks superb!
K2
K2
I now have two sets of pipes. In a compound configuration, it runs better on steam. It definitely has more power in non-compound mode. Time to work on the boiler.
Good point. Did not consider the speed imbalance due to pumping. I have some nice indexing tools for cutting gears. Old clocks can wind up storing the power of a garage door spring. I’ve had to make a gear or two.Hi Doug: Here goes:
As compound running means you are only filling 1 cylinder from the boiler, and I was using a longer stroke, the numbers now work out at:
- Bore: 1.2”
- Stroke: 2” = double acting;
- Compound running configuration.
- Crank speed: 300rpm.
- Steam pressure 20psi (guessed from what I think I can see on the pressure gauge?).
So:
This gives me 636 cu-in of steam per minute... which equates to 0.88 cu.in. of water per min. (at steam NWP = 20psi). This also proposes a need for 0.6kW of heat developed into steam. (at 60% efficiency, because the boiler loses heat to the room, heat is lost up the chimney, etc. you need a 1.1kW burner).
Now translating the 0.88cu.in/min. of water:
a pump at 250rpm would need a displacement of 0.0035cu.in. per REV.
So a single-acting pump, stroke = 1/2", would be 0.095in bore... IF I have crunched the numbers correctyly! (I can't even type correctilly!).
The way many manage this is not with a direct acting eccentric/pump, but with a geared shaft that has the pump attached. The tiny bore (~3/32"?) will have some dead spaces at "TDC" (due to valves etc.) that will cause it to not function if they have any entrained air. The draw-back then is that the engine can appear to speed-up in the "intake" stoke, and slow on the "pressure" pumping stroke when it is working against boiler pressure. I compensated for this with a weird eccentric drive motion that gave the pumping time approx. 3 x the inlet time... and evened out the pressure variation somewhat.
I'll have to strip the system to show you with picture and video.
K2
I like the concept. That’s exactly what this engine needs. I would have responded sooner, but I was asked to play in a pit orchestra for a show opening this weekend. The proceeds of course go directly into my projects.Hi Doug (and watchers all!).
Just a quick post as I am off out with my beloved lady to enjoy the sun!
Here is a VERY quick sketch (NO CAD!) to indicate how a simply wheel driven lever can vary between one stroke and the other for the pump.
Rotate the pin clockwise in your mind (or YOUR CAD model!). When the drive pin approaches l1, it has a good velocity ratio for quick priming of the pump, sucking against atmospheric pressure.
As it approaches L2 it has a very good mechanical advantage to push against the pressure in the boiler.
Hope this makes sense?
K2
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