Re: [new_distillers] needle valve size - 3/8 or 1/4 or 1/8 does it matter?
- Gotcha. Thanks Mike!
----- Original Message -----
From: "Mike Nixon" <mike@...>
Sent: Saturday, March 01, 2003 2:33 PM
Subject: Re: [new_distillers] needle valve size - 3/8 or 1/4 or 1/8 does it
A bit of head of liquid. Mount the needle valve so that there are a few
inches of liquid above it, eg in a feed tube. This increases the pressure
differential across the valve and that overcomes any tendency of the valve
to "stick" due to surface tension or a stray bubble. All sizes need this as
when the valve is almost closed, they all offer a very small area through
which liquid can pass. The diameter of the feed tube doesn't make any
difference ... it's just the distance above the valve that does.
----- Original Message -----
From: Bob Bourne
Sent: Saturday, March 01, 2003 4:15 PM
Subject: Re: [new_distillers] needle valve size - 3/8 or 1/4 or 1/8 does
Give it a bit of head to work on Bob. Those small needle valve can be
erratic when surface tension or a small bubble gets in the way.
Sorry Mike, not quite clear on what you mean here?
Are you saying 3/8 OK, 1/4 OK maybe, 1/8 dodgy bubble prob?!
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- The size of the needle valve CAN matter - depending on how much
power you are putting into the boiler. snd whether or not you wish
to strip as well as rectify with your setup.
For example - a kw of power will produce somewhere between 35 and 80
ml/min of condensate (depending upon ABV). Check the capacity of
your needle valve wide open (with the same liquid head you will have
when installed). If the valve cannot pass as much liquid as the
still will produce, then it is too small!
There is quite a bit of variation between different needle valves of
the same nominal size.
The other difference you will see between the sizes is that the
bigger the valve, the touchier it is at the extreme low end of its
flow capability. You need to find the best compromise between
maximum capacity and low-end controllability.
- BOKAKOB wrote:
Subject: Re: [new_distillers] needle valve size - 3/8 or 1/4 or 1/8 does it matter?
1/4 - yes
1/8 - too small if it exists
Bob Bourne <bourne@...> wrote:
The inline reflux column I'm working to (Nixon) calls for a 3/8 needle valve. Can I use a 1/8 or 1/4 instead? Bob.
==================================Alex is right, for the size of still most of us use, for reasons given earlier by Mike McCaw ... the size needed to be able to cope with whatever your still is capable of producing. I had assumed that factor to be self-evident when I said that any size would serve.I personally use a 1/4" with my LM rig (the 1/4" needle valve is a common item for gas fittings here) and find it works very well. However, I do not use that rig for stripping, so the valve only has to be able to cope, at the most, with 20% of the total that the boiler/column/condenser produces. A 1/8" needle valve is getting pretty small, but would work fine for a small, low power rig.Mike M's rule of thumb should help you decide on the maximum flow rate you can expect: "a kw of power will produce somewhere between 35 and 80 ml/min of condensate (depending upon ABV)" Use those figures if using the rig for stripping as well as purification, but divide by 5 (7 and 16 ml/min/kw) if the rig is used for purification only.His advice about control of small flows should then help you decide on the best size for your purposes: "the bigger the valve, the touchier it is at the extreme low end of its flow capability", so use the smallest valve you can get that can cope with the maximum flow rate you expect.Fot the best of both worlds, use a T-junction and mount a large needle valve in the bottom line and a small one in the side line. The procedure to use with this arrangement should be obvious.Mike NMike N