Vapour Locks on Downcomers

edited June 2013 in General

I am currently building (very slowly due to other life commitments) a small 3 plated column with valve plates. Mostly for clear fruit brandies.

I went for central downcomers, and following other discussions have fitted cup type vapor locks. This is to ensure that the depth of liquid inside the vapor lock is deeper than the depth of liquid held on the plate above. And yes I also included a weep hole in the vapor lock cup, which now seems might not have been a good idea.

What are your opinions on the issues of depth of the vapor lock relative to plate liquid level, and vapor lock weep holes?

image image image image

The downcommers need to be trimmed a bit to reduce the liquid depth on the plate to about 20 mm, they are currently set at 30 mm.

For a hexagonal column made from sheet.


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  • My downcomers are about the same size as my riser, though I do notice on runs the condensed vapour is about 1/4 of the way inside the downcomers, not level with top. I cant see a weep hold working, the vapour finds every little hole it can to get back up the top.

  • edited June 2013

    How about the hole in the side of the downcomer instead of bottom? Would that make any difference on how easy the vapor can enter. I do realize vapor is going to find the easiest path just a thought.

    It is what you make it!

  • I quite deliberately placed my weephole at the edge of the trap, and the intention was that any vapour bubbles passing into the trap would just end up back in the same vapour space from where they started, and not pass up the downcommer into the vapour space above the plate. That is why the cup is not centred on the downcommer.

    Whether this works I don't know, but I am hoping that the constant current of reflux through the downcommer will prevent any vapour from passing through the downcommer tube thus by-passing the plate.

    The illustration above is exaggerated, the gap between the bottom of the downcommer tube and the base of the cup is less than a 1/4".

  • Makes sense and did not see that possibility!

    It is what you make it!

  • The one issue I see with this design is that the center DC will not force the fluid to cross the plate before it can drop down the next DC. You will basically overflow the top plates DC cup and that fluid will be right around the next DC opening on the next plate.

    By having the DC on one side and then then next one on the other side you force the reflux liquid to pass across the plate before it can fall to the next level. This give the plate the chance to reheat the fluid and concentrate the vapor on that plate by extracting more of the available alcohol before it drops to the next plate below.

  • Good point RDD, you need a little roof Myles lol.

  • That is OK and is an easy fix, but from some of the videos I have seen these plates can be really active. Will have to see how turbulent these are when in action. These plates are only 5"+ across the flats, same cross sectional area as a circular 5" plate.

  • I reckon a little hat on the downcomers like a Chinese man's hat, would direct the falling distilate onto the most active areas.

  • I reckon your going to have a minimum level that will give enough weight for the valves to seat and seal, but I don't think you are going to have a maximum from a functionallity point of veiw.

    Miles, I had no luck when I tried weep holes, if they work for you, I might copy them. I've heard of cases where they work, so theres a good chance they will. :-bd

  • Something I shall consider-test are: First Fully sealed the bottom end... then see how many 1.5mm hole you have to drill for it to be enough fix the reflux so the plate note flooding abowe, this is a balancing act for the more holes in bottom the more steam can "go" this way if it is zero reflux ...

  • The smallest drill I own is a number/gauge 80 (0.0135")(0.34mm), and there are smaller than that available. Surley something that small would work??

  • RDD is correct. The returning /distillate can shoot right down the overflow tube. This can promote smearing. We experienced this with our first plate design. Can resolve if this happens by installing a tee upon your overflow riser. Would be best to alternate the orientation from left to right as RDD mentions. Beautiful work otherwise Myles

    StillDragon North America - Your StillDragon® Distributor for North America

  • do you remember pintoshine's version of a bokabob? The one with the mushroom shaped splitter. I am going to borrow that concept for putting a reflux diverter over the top of the downcommer hole.

  • I have drills down to number 100... they make a 80 to 100 drill index.. is about the size of an american half dollar with all the drills in it...

    myles a small copper umbrella would work as well over the downcomer....

  • @Myles said: do you remember pintoshine's version of a bokabob? The one with the mushroom shaped splitter. I am going to borrow that concept for putting a reflux diverter over the top of the downcommer hole.

    Nah, cant remember, care to share?

  • edited June 2013

    Take a relly good and close look on this 3pc foto....

    image image image

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  • Something to consider is that in all large columns with adjustable height on the plates by using the handle from outside, then will return liduid dumps in-at the same place on all the plates below .... But the have allso only 1pc BIG bubbelcaps...


  • edited June 2013

    @emptyglass said: Nah, cant remember, care to share?

    Hope he doesn't mind me reproducing it here


    The full album is here.

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