First run not going to plan

[benja]

OK so I finally got around to running my air cooled still, but it's not going as planned.
I can't get the input power above 300W without vapour escaping the top of the column. At this power, the boiler temp is 89deg, between plates is 78.5deg, with the temp in the middle of the lower cooling cluster around 55-60deg, and the temp in the centre of the upper cooling pipes at about 45deg. Output is perfectly cool, the top of the column is cool to the touch. If I put any more power in, the vapour can be felt in the top of the column, and the temp rises as well. With the needle valve fully open, takeoff is about 80 drops a minute. There is very little difference in temps with the valve fully closed, and I suspect at that rate there is little reflux going on since there is so little vapour being condensed. By my reckoning, there is still some capacity for the cooling pipes to do their thing, but the vapour is moving past them too fast at higher input powers and vapour speeds. Column is packed with structured copper for 700mm, with about 150mm clear space above this before the plates.

I am wondering if extending the height of the column above the cooling pipes would increase the time the vapour has to cool and condense, or if there are any other tweeks anyone could suggest to improve the production rate. After all the work that went into this still, I am loathe to scrap it and start again, but the increased in performance over the previous model just isn't there.
Any suggestions greatly appreciated.

Cheers

Benja

[benja]

Sorry, probably should mention product is coming off at 88%, which is OK, but I am looking for something much better. My last still consistently got 93%+, but it was even slower, and took about 18 hours for a 14% wash.