mors9

Hmm yeah thanks. Gives me some stuff to look at. We just had the returns redone as separate returns because they were plumbed together originally. There are no vents or traps... But it could possibly be that the connectors are not air tight. So I'll start there at least.

The downtubes are roughly 28 inches long.  So they extend about 25 inches below the liquid level (when full.)

They enter the boiler about 3 inches above the liquid level. Once the piping enters the boiler it just does a 90 degreen elbow and straight down into the liquid.  Roughly 3 inches away from the sidewall. 

The entrance point for the drain at the bottom of the columns is roughly another 5 inches above the return... so a total of about 8 inches over the liquid level.

We do not have any pressure measurements.  Not sure how to take them.

Here are some videos of the issues we're having. Along with a trace of the return piping.

https://drive.google.com/folderview?id=1cpeg5V18yqvERPz2s_NdmYw26BU3Xptk

Thanks for the replies.  @Stumpy I'll check out the pics and solution for sure.  Glad to hear I'm not just crazy and others experience this issue as well.

@meerkatThanks, I'll read up on that thread.  Our columns are above the liquid level in the boiler typically (Unless we really really fill the boiler up to the manway.)

Hey,

We have a 1000L steam jacketed still with 2 12 inch columns.  They are run in series meaning the vapor path of the first column enters the bottom of the second column and then exits the second column and enters the condensor.  Each column has a deflegmator with the water run in parallel.  Each column has a return pipe in the bottom for the reflux to return to the boiler.  This return pipe dips down below the surface of the wash in the boiler.

The issue we're having is the refulx return in each boiler pulls wash into the boiler and doesn't allow the refulx to return to the boiler.  This causes the columns to flood from the bottom up.  We've tried reducing the steam pressure to almost zero and the issue still persists so it's not that we're running too hot.  Anyone have any thoughts on what the issue could be?  Maybe something obvious I'm missing.  Thanks.