I see that I have not kept up with the updates.
I made a "mold" of sorts to fabricate a decent pitot-nozzle.
Pretty much a simple piece of roundbar 4 mm turned to a cone.
Coated the mold with wax, wrapped a bit of Epoxy soaked tackling yarn, and let it cure.
This allowed me to fabricate several identical nozzles, which I could drill out to size for experimenting.
1.2 mm was what I ended up with.
Secured with a bit of silicone tubing, this is the endresult:
looks hideous, but all that matters is the shape and dimensions on the inside. Those determine effectivity.
Now I still had the coil on the outside of the condenser, and that is a miserable design: Heated water releases its dissolved gasses, these gasses remain trapped in the high points of the windings, and each airpocket represents a bit of height difference, that the pitot tube has to overcome. As long as I held full throttle, the undisturbed system would keep going all by itself for about 20 minutes, then the collected air would stop the waterflow.
But even with a "fresh" system (no air build-up yet) below 3/4 power the waterflow would stall, and was very reluctant to restart on full power.
With a bit of tapping against the lines I could dislodge that air, and keep the system going, but that is not how it should be.
When reversing the engine, sometimes the waterflow would reverse, sometimes not. Also not very desirable.With this coil (1 metre of 4 mm copper tube wrapped around the condenser shell) I managed to stretch endurance from about 25 to about 30~31 minutes of continuous full speed.
So I decided, just as a proof of concept to see what a horizontal "coil" inside the condenser shell would do. Since inside most space was taken up by WAAAAAYYYY too much preheater coil, I could only fit about 20 cm of condenser tube, just once forward and back.
the result was remarkable: Despite only 20 cm of steam-exposed cooling tube, I gained another 4 minutes of full speed endurance. Absolutely not bad.
What was even better: The waterflow maintained itself, water pressure at full speed was strong enough to dislodge any trapped air. Waterflow easily and reliably reversed itself when the machine was reversed, and at least in forward direction, waterflow kept going reliably at 3/4, most of the time even down to 1/2 power, and restored itself every time above 3/4 power.
Next step will be to shorten and rearrange the feedwater preheater coil, in order to create more space for one extra loop (additional 20 cm) of condensing coil.
And I think I will leave it at that... 40 minutes of full power is enough.