Valve timing for oscillator

[John BramwellParticipant @johnbramwell55907]

[John BramwellParticipant @johnbramwell55907]

Hello

I have draw a twin cylinder double acting oscillating engine to pull a toy train on the flat. With a 2mm ports positioned so that they fully coincide at mid stroke (90 deg) there is a 33 deg delay before commencement of opening. Should that be reduced by elongating the cylinder port? I built one without such elongation but that did not have any load and had a heavy flywheel. (FYI 8mm bores 20mm strokes). cheers John

[Jeff DaymanParticipant @jeffdayman43397]

Hundreds of thousands if not millions of steam toys have been made since the mid 1800's with oscillators with drilled ports open at mid stroke. They all worked fine, maybe not efficiently but certainly functional. Why worry about it?

[JasonBModerator @jasonb]

It is all down to how far the holes are from the cylinder pivot and stroke, You can have them lined up at 90deg bit starting to open at 1 degree so there will indeed be a lot of difference in performance so may or may not have the performance to pull your train.

If you can't get the holes the right distance away from the pivot then as you say elongating them is another option I would be looking for an opening of a lot less The ones I have made have opened at more like 5 degrees. Enlarging the diameter of all the holes would also work provided there ports were both closed at TDC & BDC

This is a good example of how the timing will have an effect on engine performance, this engine has a reverser as well as changing direction it also alters the cut off from about 5deg to 45degrees and you can see how much slower and I would imagine weaker the engine is as the amount of air getting to the cylinder is decreased.

 

Edited By JasonB on 04/03/2021 14:59:11

[John BramwellParticipant @johnbramwell55907]

Thanks Jeoff and Jason. I guess it also depends on the rate at which the boiler can produce the steam.

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