Re: Takeoff rate not steady
- I too have discovered this irritating phenomena. I put it down to the fact that the valve does not have a positive "set". Whatever position I rotate the handle to, I always have to tweak it. I think this is caused by the valve's stem seal properties changing when heated.
--- In email@example.com, "Harry" <gnikomson2000@...> wrote:
> --- In firstname.lastname@example.org, "geoff burrows" <jeffrey.burrows@> wrote:
> > Hi rosnekcaj,
> > It sounds like you may have a heat build up in the hot plate across the whole of the plate, as opposed to where the actual heating element is. The faster take off, has got to be connected to an increase in heat to your boiler hence more vapour flow i.e. steam/ethanol mix, hitting the condenser therefore more more water condensed.
> > As you probably already know the ethanol/steam mix proportion in your vapour is slanted to more steam than ethanol. So more water is condensed per bigger measured flow unit.
> > This means a higher water content in your distilate, so you end up with weaker product
> > HTH
> > Geoff
> I don't think so. I'm guessing it's "needle creep". It's a common fault with needle valves operating in a hot environment. They gradually expand and allow more fluid to pass. They need periodic adjustments. That's why everyone is going to Vapor Management stills. Easier to control. Pretty much "set & forget".
> regards Harry
- One thing I failed to mention is I am using a modified needle valve.
When I first ran my bokabob I noticed that the needle valve setting was extremly touchy - very sensitive - very course resolution as far as setting the flow rate.
After dissasembling the needle valve (which came from Lowe's), I found that it wasn't a "needle" valve in that it did not have a long tapered needle that penetrated through an orfice as I had envisioned. It had a tapered seat with that mated with the tapered end of the stem to stop the flow. The thread pitch on the stem was 32 tpi.
I drilled out the stem, then fabricated a long tapered needled with a shank size to create a press fit into the stem.
I drilled out the seat, and then fabricated a new seat to press fit into the hole I drilled. The new seat had a small orfice for the needle to penetrate.
Result was much better resolution in adjusting the flow rate. However, it did not overcome the variation in flow rate which Harry attributes to "needle creep".
Thanks for your comments.