What you are not taking into account Brian is that the slowest you show it running in your video would be the maximum speed the engine should run, any faster and it is grossly over scale.
Almost everyone does it, that is running their 'steam' engines too fast. The slower the better and more in keeping with full size.
You only have to look at full size steam engines running, they are usually fairly slow, except maybe traction engines and such which use fairly large reduction gears to reduce the speed, and thus allow a small cylinder to drive a large machine efficiently.
In all honesty, you would have been better using a metered taper valve, they give much better control than a straight through rotating valve, which are usually used for just turning on/off, not speed control.
You are also wrong in your quote in the video where you state the engine should first run fast, then have to slow it down. The only reason you have to run fast is because there is too much friction in your set up, a free running engine should be able to start of at almost any pressure setting that it will turn at. Maybe you need to give your engines a couple of hours run in on air (never mechanically) before deciding that your control valve is the one to go for. You just might find that when the friction is reduced, your valve will have very little control at all.
I am not being 'picky', just trying to give you a bit of advice based on nearly forty years of running live steam model engines.
John
