Needle valves can be expensive, so I thought I'd post a version of a poor man's flow control valve that is used in one of my still heads. It's a Pure Distilling liquid management reflux condenser.
Okay so this is what the take off assembly looks like:
The internals look like this:
Distillate take off is controlled with a simple stainless ball valve that has a calibrated brass fitting screwed into the valve outlet. The 'calibrated brass fitting' is simply a brass nipple that has been filled with soft solder and had a ~1mm hole drilled through it. When the ball valve is fully open, the 1mm hole lets through 1.5L/hr. Here's a pic:
This works pretty well, and is quite satisfactory for the main collection during a reflux run of low wines on 2,200W, giving you a reflux ratio of 3:1 during the early part of the run. The collection rate is higher than I would like when running a wash straight from the fermentor. And it's a bit quick when you're pulling off heads. I've found that I can get enough control to slow collection to ~900mL/hr, or 3 drops per second, which is about the rate I like to take off heads and to collect ~10% washes. If you wanted the flow to be slower than 1.5L/hr, you could also drill a smaller hole. You can get drill bits at 1/32" (0.79mm) and 1/64" (0.40mm) from hardware stores.
I'm not completely wrapped about (a) the brass fittings, and (b) the soft solder plug. Although both are safe enough, I'd prefer stainless and copper only. So I'm going to modify the calibrated fitting, replacing what brass I can with 316 stainless and the soft solder plug with a drilled piece of copper. More pics to come.
Anyway, this is one method of getting slow flow through a ball valve for those of you who can't afford a needle valve. It's non-adjustable, but it will do the job.