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Another nutty idea
PaulR:
Is there anything wrong with this idea of driving a piston type valve directly from a crosshead rather than using an eccentric or from the crank-pin? The valve travel would be the same as the stroke; it would poke out the back of the engine if proportions were similar to this but it could be shorter at the inboard side than I've drawn it here.
I suppose the valve (drawn in blue) could be mirrored across a horizontal line to make the engine double acting... maybe?!
Jasonb:
The timing will not be very good, the highpoint of an eccentric is usually set to lead the crank by about 120degrees, yours will not have any lead. Left hand image you are pumping in air while the piston is right at the end so it will never want to return.
Also as drawn you are going to end up with the cylinder open to air or exhaust for very short periods due to the small holes and big gap between. On the exhaust stroke the piston will be compressing a lot of what is in there before the exhausts opens.
Jasonb:
If it were a double acting cylinder with slide or piston valve then you could probably do something like the steam feed pumps where there are two "stops" on the valve rod that are actuated by an arm on the piston rod or in your case the cross head.
A bit like working an engine manually
http://www.youtube.com/watch?v=A-V3b1UKqCs
PaulR:
--- Quote from: Jasonb on December 18, 2025, 03:34:32 PM ---Left hand image you are pumping in air while the piston is right at the end so it will never want to return.
--- End quote ---
I omitted the valve chest - the left drawing is supposed to show that the inlet is blocked off, sorry that's not clear.
Yes I did think about the holes in the valve being bigger or maybe having a funnel-shaped mouth or even being a slot rather than a hole. Might be back to the same issue as with the other (non-working) valve-within-the-piston idea....
PaulR:
--- Quote from: Jasonb on December 18, 2025, 03:40:03 PM ---If it were a double acting cylinder with slide or piston valve then you could probably do something like the steam feed pumps where there are two "stops" on the valve rod that are actuated by an arm on the piston rod or in your case the cross head.
A bit like working an engine manually
--- End quote ---
Yep, I made something like that in the past (still got it) and it worked very well although it would only run at speed and was proper noisy as it smashed at each end! Might give that a go...
http://www.youtube.com/watch?v=tNPXCuc9uQ8
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