Strange problem, need some experienced help.

[tvman44]

I built 2 Thien style separators a few years ago, both built on  20 gal (approximate) plastic barrels and worked fantastic.  One was used on a 1hp dust collector & the other on a Harbor Freight 2 hp dust collector (1550 cfm supposedly), like I said both worked great hardly anything got into the collection bags.  Two years ago I was flooded out in the flood of 2016 and lost both collectors, I have just got my workshop set up again & replaced the 2 hp HF with  a 3 hp Grizzly collector (2320 cfm), now the separator does not work nearly as well as it did with the 2 hp HF, a lot is ending up in the collection bags.
My question is, could the higher cfm of the 3 hp unit be too much for the 20 gal barrel?  Or what should I try?  Wondering if I made another separator with a 55 gal barrel, would the larger diameter barrel work better with the higher cfm of the 3 hp collector.  Hoping some of you more experienced guys that have played around with these a lot & made a lot of improvements might have some ideas and or suggestions.

[retired2]

There may be some guys with 3hp systems that might be able to provide better data than me, but if I had to guess I would say the velocities are too high.  What size are your main lines?  Is you separator a top hat design.  Are your filter bags green?  Things will slow down a bit once your bags get some fines in them. 

Try opening a second blast gate to see if that helps.  It may or may not slow the velocity depending on the line sizes and system losses.  But if the separation improves with two or more gates open, it is a pretty sure sign that the separator is being impaired by the higher velocities.  It's a lot of work to build a decent separator, but you might need a larger diameter, and this might be a place where a 2X high separator might really show a benefit.

[tvman44]

Lines are 4", it is not a top hat, it is the original in the barrel design.  The 2 high you mentioned, is that a top hat design.  I have been wanting to try building a top hat version but my original worked so well I just could not mess with success.  This might be a good time to try a top hat on a larger diameter barrel like a 55 gal plastic I have saved up in my warehouse.  Maybe I should start researching top hat designs & 2 high also.  I really appreciate your response, I was hopping you or Phil or someone like that would respond.  I would hate to re-plumb my shop with larger diameter piping.  But a new separator might be a fun project.  I need to find more info on top hats.

[retired2]

A 3hp blower is a lot of power for 4" plumbing.  Unless you've got long lines and tight ells to eat up some of your SP, I suspect your line velocities are well above what is needed.  I think a top hat design would work much better for you.

Two things to think about before you invest your time and money building another separator.  A large barrel provides the space for a larger diameter separator, which I think would help, but emptying a 55 gal waste container can be a real chore.  Second thought is that while a 2X high separator might, and I emphasize might, be helpful in this situation, they are more complicated to build than a 1X high.

[tvman44]

Retired2, Last night I kept thinking about my problem and this morning I found my problem & feeling kind of stupid.  When I built those 20 gal separators I did not glue the elbow on the input that turns the flow to follow the around the barrel.  Evidently when they packed up all my things to put into storage (I was with my wife in the hospital & could not get home because of the closed roads, so family & a few friends came & packed up & moved my things to storage after the flood) they emptied the barrels & knocked the elbow off so the dust was going straight down to the baffle & right out the outlet pipe.  I reattached the elbow and tested the separator.  Yesterday I had dropped about 10 pieces of foam ½" thick & 1" square into the table saw line and only 2 stayed in the separator the rest all went through the blower into the collection bags, also 80 to 90% of sawdust I had run through the system had ended up in collection bags.  After reattaching the  elbow & dropped 16 pieces of the same foam into the table saw line and they all went into the separator, none into the collection bags.  Huge improvement.
In the next couple of days I plan to empty the collection bags and monitor the performance.  But for now looks like I am back in business.  I appreciate your suggestions & plan to make a top hat possibly a double height separator on a 55 gal barrel in the near future with 6" ports.  1st I want to tackle a few projects I have been wanting to do for the last 2 ½ years.  Then make that  new separator, for now I am searching for the plans for a top hat.  Maybe you have a link you could share.
What I have now is 2 4" lines in my shop each going through it's own 20 gal separator through 2 4" lines to the blower.  The blower has a 6" inlet with a adapter to 3 4" openings, so I am using 2 4" lines to the 2 separators.

[retired2]

Sounds like you've had your share of problems recently.  Hope all the bad luck is behind you and now you can spend some time relaxing in the shop!

I'm glad you found the answer to your separator problems.  It's pretty easy to understand why it didn't work without that critical elbow.  As much as I didn't think velocity should be the problem, it was the only thing I could come up with.

As far as a link to a top hat design, I suggest you use the plans in the most read thread on that subject - mine!😂  You don't need a link, it is easy to find on the second page of threads. 

[tvman44]

retired2, I have been reading some of the thread on your top hat build and have 2 questions.  It is probably in the thread but I missed it, what is the diameter of your pipes in & out, also how high is the separator chamber?  I have some laminate on hand (formica) that I am thinking of using instead of clear if it is long enough, any disadvantage to that other than no visibility into separator.  Thinking about building one with 6" lines, so a 2x would be 12" high????

[retired2]

My plumbing is all 5".  That is kinda the sweet spot for 1-1/2 or 2 hp blowers.  If you start replumbing your system 6" is what you should use.  All the dimensions for my separator appear on the simple sketch in one of the very early posts in the thread.

I'm not sure there is a hard and fast rule about the height of a 2X separator, but nominally it is double the inlet size.  But there isn't any rule that says it can't be 2-1/2 times the height.  The only practice that seems to be followed by everyone is to put the inlet in the upper half of the separator.  For what it is worth more than one person has said the 2x high separator works better, but I have yet to see hard data, it's all subjective.  Now having said that, if I were to build another one that is what I would build.  Why?  Because I have never heard anyone say it doesn't work as good!😊

[tvman44]

The top hat foe 6" is on my to do list, just not at the top of my list.  I wonder if 5" would be better with my 3hp blower or should I go with 6".  I need to read a lot more on this while I catch up on some other projects.  I appreciare all your comments & welcome any further comments & observations.

[retired2]

I'm pretty sure your 3hp blower would do fine with 6", unless you have unusually long runs with lots of tight turns.  You could probably use 5" as well, but depending where you are located 5" fittings can be hard to find.  I was able to find laterals locally, but I had to mail order all my long radius elbows.  They are expensive!