Aaaaaw cmon guys - please answer my question

[Howard In Toronto]

Hi all -

Lots of views. But no replies. So I thought I'd try this post again. I hope somebody will take a moment to answer my questions for me

I use 6-inch hose and would like to enter the double-height Top Hat in a rectangular opening. I plan on using a 6-inch HVAC boot. The "exit" is4x10 inches.

I have 2 questions -
1 - how much does it matter if the 6-inch hose enters the Top Hat close to the center vs the top
2 - the area of a 6-inch circle is 28.25 square inches
The termination of the HVAC boot is 40 square inches
How important is that difference

I'd really appreciate if somebody could take a moment to answer my Qs.

Thank you.

Howard

[tvman44]

Hello, wish I could help but I honestly don't know.  I did not build a top hat version yet.  I have built 2 in the barrel types and love them..

[Schreck]

"1 - how much does it matter if the 6-inch hose enters the Top Hat close to the center vs the top
2 - the area of a 6-inch circle is 28.25 square inches
The termination of the HVAC boot is 40 square inches
How important is that difference?"

1 - If "close to the center" refers to the vertical dimension, then that should be okay.  I don't recall much discussion about the merits of entering a double height top hat at a high vs. low point.  Lots of warnings about trapping shavings between the transition and baffle, though, so leave a space between them.
2- the HVAC boot is a transition from a small cross-section hose to the much larger volume of the top hat, so the fact that the rectangular end of the boot is larger is good.  The primary purpose of the transition is to direct the air and dust flows to the perimeter of the top hat, which it will do.

[retired2]

I have no experience with a double high build, and I have not seen any test results on the two most important variables, the position of the outlet and the position of the inlet.  So, with that in mind here is my two cents.

If the argument for a 2X separator is that the extra height provides more time for the centrifugal force to separate waste from the air stream then it would seem logical that an inlet that is set higher serves the purpose better than one set lower.  Why set it lower and shortcut the distance to the outlet?  For the same reason, I would put the outlet pipe at midpoint or below, but I would build the separator so I could test a few positions before I lock it.  If you've read the thread on my build you can see it is not that much trouble to build a separator with an outlet that can be moved for testing purposes.

As "Schreck" has already said, a transition from round to rectangular is better if the rectangular area is larger than the round area.  That comes from a rule of thimb for ductwork design that says rectangular duct is less efficient than round, and to compensate the rectangular area should be 10% larger than the round area.  Now, since the length of the rectangular section of a transition piece, or boot, is very short it probably doesn't matter that much.  However, I definately would not make it smaller than the 10% rule of thumb - no point in introducing unnecessary line loss.

[dragonflight]

I have a friend who says that there are only two types of people in the world.
Those who know they don't know and those that don't!
I try to stay in the first camp, but I wander and the only thing I really know about fluid dynamics is that it seems to be forever surprising!

With that in mind and proclaiming that I have not built anything (yet). I offer these (perhaps useless/incorrect thoughts)

a) as for the entry height, as retired2 says, surely you want the entry at the top.

b) I think that both retired2 and Schrek (unlikely though it would seem) may be missing the fact that a big factor in the separator is the speed of the airstream in the separator, so making the inlet too big MAY be detrimental to separation performance. As the boot is 40% bigger than the duct the air will slow down. It is a short transition so by how much who knows. I have kind of asked the same question - performance and SP loss vs airspeed and volume

According to Bill Pentz it is not that hard to make a transition from sheet steel (at lowes galvanized cold return joist covering @$8 for a 16"*36" piece is probably big enough for 2 tries)
BTW at a w:h ratio of 2.5:1 the inefficiency of rectangular duct is about 5%

So, really a non-answer, but maybe food for thought.

I intend to have a rectangular inlet and rectangular ducts so I hope to try a few experiments, but summer (and boating season) is almost upon us so it may languish into the fall.

mike

[retired2]

dragonflight, you caught me on a really bad day, so let me start by apologizing for my response.  I try to help as many people as I can, but it does wear you down trying to help everyone.  And it doesn't help when you get someone like Howard who begs for help and when you go out of your way to respond, he doesn't even acknowledge that he's read it.  I don't need a thank you, but it would be nice to know I didn't compose a response for my health.

The more immediate problem I have is in a matter of days every photo I've hosted on this and other forums is going to go dark if I don't do something quickly.  I've started that process today and it will take every minute of my time.  I am focusing on this forum first because without the photos many of my posts will not be of any help to anyone.  So, I can make the biggest contribution doing that rather than answering questions.

Now, all that said, I would suggest you do a search and filter for my posts.  At one time or another I have either asked or answered many of the questions you need help with.  The truth is many questions don't have absolute and answers.  People do things on a trial and error basis.  But the two separator styles after much tweaking still follow most of the original rules of thumbs.  If you read enough posts, you will soon be able to answer your own questions.  While I have a heavily read thread of my build that I recommend you read, I am not an expert - I've built only one separator in my life, and that is a little light for expert level experience.


Regards, and forgive me if I'm a little short today.  What I have to do would put anyone in a bad mood.

[dragonflight]

Retired2,

First of all I read about your troubles with the pictures and I agree what a ridiculous pain, it puts me in a bad mood just thinking about it!

Second I am a little bit confused by your response, not sure if you are replying to this post (Howard's) or my own, not sure if I offended you - which I can ensure you was not intentional, and not sure what you are apologizing for except maybe implying that I would be inconsiderate enough to post questions with out having made an attempt to first find the answers on my own.

Without wishing to be defensive I will say that I spent 20+ hours reading posts on this forum (and I am  a fast reader) including many of your posts/responses and joined 2 days ago to use the search feature (though I did get screwed up with forum vs thread search) and probably an additional 10 hours since then, not to mention a whole lot of youtube time wasting - yes I can be "slightly" obsessive about stuff.

While you made not need a thank you, I would like to offer a thank you for your very long/detailed post and especially for taking the time to take AND share your measurements as well as sharing your thoughts many, many times

mike

I would appreciate a reply - just so I know-, but thoughtful replies take time and I will not be even slightly offended if you were too wait until after you recover from picture hell.

[retired2]

Mike,

Absolutely no offense from anything you've said.  I was just venting about Howard not taking the time to acknowledge three posters who responded to his appeal for help.

I am glad you have spent a lot of time reading the forum posts.  There is a lot of good info here, but unfortunately there is no good sort or search mechanism to get directly to the info you need.  Many times it is buried in a thread with a title that would not give you a clue it is there.

My bad mood is not just photo link hell, but I'm laying on a heating pad nursing a sciatic nerve problem as I write this.  It is hell to get old, you always have some ailment and then you get grumpy. 

Now I realize I didn't even read your post.  I jumped to the conclusion you reposted your other post asking for help in this thread because of it's title.  Now I realize you too were helping Howard.  No wonder you were confused by my comments.  They probably would have made more sense in the thread you started.  Oh, well I started by telling you I was having a really bad day!

[tvman44]

"Getting old is not for sissy's"

[retired2]

"Getting old is not for sissy's"

I would probably be in a lot better shape if I had been a sissy all my life instead of abusing my body, but at 72 I'm still thinking stupidly that I am invincible!

[Howard In Toronto]

Hello everybody.

Thank you all for your help.

For those who were offended by not hearing back from me, I apologize. For the last few weeks, I have been on the road visiting what seems like every single gumboot town in Ontario since I posted my second request. Not too bad for snow or cold, but long days and lots of driving punctuated by many, many meetings. By the time I crawl into hotels/motels for the night, the last thing on my mind is my shop because I still have a few more hours of work.

I appreciate your answer. I just didn't have enough brainpower to visit this or any other wwing forum. Do not take my lack of response as a lack of respect. And don't use my tardiness as a reason to hesitate before helping other people with questions.

Tonight is my second evening at home. I have a wife that needed some attention. And two boys that are busy forming themselves. As much as they deny it, they want someone at their elbow guiding their hand in life. All that takes time and focus. I'd like to read everybody's answers and then come back with any subsequent questions if I may.

Sincerely,
Howard