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[Vodkaman]

You mentioned turbulence in the accumulator. This is obviously causing some losses as turbulence is never a good thing. It may be prudent to fix this first, as you do not know to what extent the accumulator losses are affecting things.

One step at a time. If you fix everything at once, you will never find out what worked and we (the viewers) learn nothing from your experiences ;D

Dave

[RCOX]

Phil: So many choices and with my limited knowledge of suction loss due to sharp radius turns, size of pipe restrictions etc. is enough to boggle my mind. I went with the 6" pipe size through the separator because it is 2.28 times larger area wise than 4" and I wanted to not have to completely replumb my shop. That would probably be the smart thing to do but at this time I am not in a position to do so. I work in maintenance and actually Vodkaman's approach is the way I do all my trouble shooting to repair equipment. There has been a lot of good info put out there and I will admit, I was looking for the easy way out. Give me the answer don't make me figure it out myself. I have been the most concerned about the accumulator knowing I should start by replacing it. Chuck had a very good thought about going with 2 separators but I have been down that path except, with the Rockler type setup, not your design. I think I will probably put my experience in troubleshooting to work and see where it leads. Maybe in the end I will have all new plumbing throughout maybe not, but I will have gained a lot of knowledge in dust control (good or bad).

Vodkaman: thanks for the smack up side the head. Will post results as they progress.

[retired2]

Phil: So many choices and with my limited knowledge of suction loss due to sharp radius turns, size of pipe restrictions etc. is enough to boggle my mind. I went with the 6" pipe size through the separator because it is 2.28 times larger area wise than 4" and I wanted to not have to completely replumb my shop. That would probably be the smart thing to do but at this time I am not in a position to do so. I work in maintenance and actually Vodkaman's approach is the way I do all my trouble shooting to repair equipment. There has been a lot of good info put out there and I will admit, I was looking for the easy way out. Give me the answer don't make me figure it out myself. I have been the most concerned about the accumulator knowing I should start by replacing it. Chuck had a very good thought about going with 2 separators but I have been down that path except, with the Rockler type setup, not your design. I think I will probably put my experience in troubleshooting to work and see where it leads. Maybe in the end I will have all new plumbing throughout maybe not, but I will have gained a lot of knowledge in dust control (good or bad).

Take a look at the photo below showing part of my DC piping.  In particular look at the manifold above the floor sweep and jointer.  Now imaging that turned upside down.  That is what you should build.  Get rid of the accumulator and put in two sweeping bends into two 45 degree laterals.  I assume you have blast gates at each piece of connected equipment and only one of the 4" lines is open at a time.  If so, I don't know what two separators is going to do for you.

[RCOX]

Retired2: I had thought of a similiar setup after Vodkaman's suggestion but had not thought of 2 wyes with 45s and an end cap. I was trying to picture 1-45 off of the leg of the wye and 2- 45s off of the end to make a sweeping 90. I think either way would eliminate a short 90, which will take care of the inlet side. Then I can start working on replacing the outlet side short 90s with sweeping 90s. I want to thank everyone for your suggestions.

[retired2]

I assume you have blast gates at each piece of connected equipment and only one of the 4" lines is open at a time.  If so, I don't know what two separators is going to do for you.

The reasons that I suggested two Separators is his Dust Collector has a 8" inlet, plus it moves alot of air. How big of a Separator drum to you think that you'd need to have an 8" outlet going to the DC and an 8" inlet in the Separator ? So I figured go with two managable size Separators, especially since he's useing two main trunks.

Chuck, I'm not sure I saw confirmation to my assumption that only one 4" line is bing used at a time.  If both 4" lines are operating at the same time I can see your point about two separators. 

However, if only one of those 4" headers is operational at any one time, then only one separator would be operational at a time, so why have two.

I must admit that DC does look like overkill for a system built of 4" pipe and I'm surprised that adding the accumulator and separator produced a noticable drop in performance.  It seems like we have a big air mover that is suffocating.

Rcox, If you only give your DC air from one piece of equipment at a time, try opening two blast gates simulateously, or even three, and see if the performance of your system improves. 

What's the SP and CFM rating on your DC?

[RCOX]

retired2: I do not recall the sp, but the cfm is rated at 1900. Before I built this separator, I had tried opening 2 gates on the same line with a resulting loss at any given tool. I understand you can only get so much air through a 4" line regardless how many gates are open. I just know the suction I had when using the original splitter that came on the dc and a 35' piece of flex hose that I moved from tool to tool and what I have now. I kept tripping on the flex and decided to try a central hard line setup. Because of installing the 2 main lines as I did I thought of using the accumulator and going to the 6" line through the separator to the dc. I decided to give the separator the old redneck test yesterday and trying to make it as accurate as possible so I disconnected the separator from the accumulater and placed my hand in front of it to check suction, then I disconnected the separator from the line to the dc and checked it the same way. Very noticeable difference in the loss caused by the separator. May need to look at what I have wrong there before going further. I wanted to test it this way because it takes all the elbows into consideration and just shows what the separator itself looses.

[retired2]

Rcox, you have a very good DC with far more capacity than the typical small shop.  I checked the Powermatic website and if I had the correct model, you have over 11 inches of SP.  By comparison my system is 1200 CFM and a little over 8 inches of SP. 

I have been building my system over that past year and only now am ready to build the separator, so I can't comment on what to expect in suction loss due the separator.  I can tell you I have one long run with pressure losses the just about reach the limits of my system, so if the separator adds a lot of loss, I may have problems.

Having said, that your test of your separator does seem to suggest a problem of somce kind.  I would not have expected much suction loss when it is close coupled and no other loads.

The other thing you should be thinking about replacing your 4" mains with at least 6".  You've got the equivlent of a fire truck pumping water through a 1/2" garden hose.  Snap lock pipe doesn't cost that much more than plastic pipe and you can get long radius ells.  I'm sure you don't want to start tearing out a system you just installed, but longer term that should be a goal.

[retired2]

I'm not so sure that an 8" inlet on the DC would support two 6" mains, I was thinking that two 5" mains would be more appropriate, a 5" line would support two 4" gates being open, but I wouldn't leave more then three open at a time on the whole system.

Chuck, my suggestion on 6" size was still based on the assumption that he is only running one machine at a time, so no matter how many 4" headers are coming into his accumulator only one is open at a time.  If that is how he is running his system, 6" headers are a good compromise because that size pipe and fittings would have significantly less static pressure losses, and it would be readily available at prices that are still reasonable.  By contrast, I doubt you could find much of anything in 7", and 8" probably gets a little costly and far exceeds the needs of his worst case user.

If he is running both headers open simulatneously two 6" headers only exceeds the capacity of the 8" inlet by about the same percentage as two 4" headers exceed a 5" inlet.

[retired2]

Actually Chuck, I think we are in total agreement.  He's got a great DC, but to get maximum efficiency out of it he has to give it more air.

[RCOX]

All good suggestions. Due to some extenuating medical circumstances with my wife I am limited on what I can spend, until we find out the expenses.

With that said, and I don't mean to whine just something we have to contend with, here is what my final plans are.

I will replace the accumulator with a 6" wye, bringing my 4" lines into it at this time. This will effectively make 1 "short" main line with the old mains branching off of it. This will make it very easy for me to start switching out to a 6" main as time and money allow.

Chuck, the separator drum does cave in moderately as long as I leave at least 1 gate open. If I close the entire system it will completely collapse the drum. I used a puffer bottle with talcum powder to check for leaks around the lid. I could detect no leak with the slight caveing in with 1 gate open, if I close the whole system and collapse the drum it does have a major leak around most of the lid.

Replacing the accumulator with the wye may or may not make any difference in the suction at any given tool, only time will. I will try Chucks idea about lowering the baffle and see if it changes the restriction and resulting suction. If I do not get the change I expect/need then I will remove the separator and run the 6" inlet straight back to the dc until I can get my shop replumbed and then I will start over using a different drum that will not collapse. Probably something like one of the thick walled blue 55 gallon drums that are almost indestructable. In my opinion, changing the duct work sounds like the very first step to achieve the potential of my dc. In the end I will have 1-6" main line with a branch going the each tool. Some tools I will probably leave with a 4" port and some, like the table saw I will probably cut in a 6" port.

I think I have learned more about how my system should work and what I need to do to get there. I would like to thank all for your input and help. A work in progress is what we have here.

Will post the results of lowering the baffle sometime next week.

[retired2]

All good suggestions. Due to some extenuating medical circumstances with my wife I am limited on what I can spend, until we find out the expenses.

Rcox, sorry to hear your wife is dealing with medical issues.  I hope all goes well for both of you. 

[pitbull]

6" main ducting is the answer to your problems.

The 4" duct can only flow a best case scenario max of 400 CFM while a 6" duct can do double that at 800 CFM. There is probably not a single tool in your shop than needs more than 800 CFM. If anything a widebelt sander would require it when it has 3-4 4" or 5" exhaust ports.

The brute garbage can will withstand the force of this with zero problems, however having something like your DC pulling  as much vacumm with a choked airflow will cause issues. A simple spring loaded bloow off valve could be built into your separator would solve this should the situation arrive.
http://www.jpthien.com/smf/index.php?topic=198.0

You could have 400' of duct work in your shop and as long as your runs were no longer than 30 feet your powermatic will not blink. Also, consider that you may not want to completely air tight seal all of your joints near your terminating drops. This will allow a little extra bleed as to not starve the beast when running only 4" pipe. However all joints along the main should be very tight.

The SP and CFM power of your powermatic will over come any issues with branch lines, elbows and wyes running 6" main ducting as long as you do it correctly and give you a constant max flow CFM that the duct is capable of.

6" (I believe 26ga) HVAC ducting is available at Lowes for a lot less money than spiral ducting and has worked just fine in the 3 shops I put it in.

[RCOX]

Chuck: what is the optimum distance the baffle should be from the outlet pipe? I picked up some stand offs/long nuts whatever you want to call them to be able to add the length needed. If I remember correctly the baffle is currently 3 1/2" below the outlet. I will be working on it Tuesday and Wednesday.

Pitbull: I bought a 6" hvac wye from Lowes today to start my changes. You are correct about the price being lower. The wye was $10.98 + tax, I have already  used some ells and they are only about $7.00 for 6". My makeover starts Tuesday.

[RCOX]

Well boys and girls here is the first go round of findings. First let me say I was blonde before I turned gray at around 23. I will also man up and admit my mistakes.

The first thing I checked for was leaks, yes I found some detectable leaks around the lid, also some at the joints of the adjustable ells. No, I didn't fix them. Remember, 1 thing at a time. I also found that my baffle was actually even with or slightly higher than the bottom of my input. May or may not lower suction. Now for the largest thing. Chuck you were correct, my baffle was only 2 1/2" below the outlet. I really thought I had measured it but apparently not. The outlet was through the top 3", 1/2 the diameter of the pipe but I must have guessed at the rest. I did notice a very small amount of fine dust on the under side of the baffle.

I lowered the baffle to 5" below the outlet, which put it below the inlet +/- 2 1/2".  Using the redneck test there was a noticeable increase in suction at the inlet vs only the line between the separator and dc. Also manifested same increase at the farthest point from the dc. Using that point for all of my testing I discovered that there was satisfactory suction for all my needs. Now here is the rest of the story. I noticed the turbulence in the accumulator to be about the same as it had been, when I opened a gate on the other line the turbulence smoothed out but I lost more suction than with it closed. It appeared to reduce suction about the same if it was partially or completely open. Better to leave the second gate closed. I also noticed that the entire bottom of the baffle was covered in fine dust. I tried changing the distance of the baffle from the outlet pipe from a measured 4" to 5 1/2".  It seemed that the closer to the bottom of the inlet the less dust stuck to the baffle. How far below the inlet should the baffle be? I can cut off the outlet some if I need to, to be able to maintain the distance between baffle and outlet pipe. I also noticed that there was a change in amount of dust under the baffle depending on how I placed the wide portion of the baffle in relation to the inlet. Using the lexan window I put in the side of the can it was also interesting to see how the airflow swirls in the can in relation to where the baffle is placed also. Placing the baffle so you have the maximum amount of wide surface in front of the inlet cases the dust to swirl upwards and pile the dust in a swirled ridge while placing the wide portion where the inlet is in the first third gives you a more flat swirl and lays the dust flatter in the bottom. I don't know what all this means yet but it has opened my eyes. Will have more time to play around with it tomorrow. More to follow. Any suggestions from this rambling will be appreciated.

[Vodkaman]

These are only my ideas and opinions and should not be taken as fact or gospel. I throw them out there for discussion only.

First off, great post, full of good information.

Accumulator – here is a highly speculative and over simplified diagram of what I think is happening inside the accumulator. On the left, a single inlet open, on the right, both inlets open.



When the flow passes a sharp corner, edge or even a sharp bend, a low pressure is generated on the lee side. This is caused by the air having momentum. The air wants to travel in a straight line. However, some of the air is pulled over by the low pressure, effectively reducing the diameter of the inlet pipe. This peeled off air has nowhere to go and quickly degenerates into chaotic flow or turbulence (red). All the sharp edges on the lee side of the accumulator just make things worse, churning up the air. Some of this turbulent flow will oppose the main flow and slow it down some. The same thing happens at the edges of the inlet and outlet pipes (blue). Even a regular ‘Y’ will have this turbulence, it cannot easily be avoided.

With both inlets open, the main turbulence (red) is replaced by a different pattern. It is more organized and so appears to be less of a problem, but it is still destructive to the flow efficiency. This flow is called vortex shedding and it alternates left and right (this should be visible). If you Google ‘wiki vortex shedding’ the first entry on the list will be a Wikipedia page, at the top of that page, you will see an animation of what is happening.

Here is the link: http://en.wikipedia.org/wiki/Vortex_shedding

As the vortices flow downstream, they constrict the middle of the outlet pipe (until they eventually merge into the flow), effectively reducing the diameter. Even though they look harmless, this is probably causing more of a problem than the single inlet in the left diagram.

There are things that can be done to reduce the problems: Extending the inlet pipes in at an angle, until they touch, should remove the vortex shedding problem. Filling/fairing all the corners will reduce the blue disturbances, but the best solution would be to fit a proper ‘Y’.

Inlet and outlet relative height – I am not convinced that this is significant. The inlet flow will take the easiest route, which is down the centre of the chamber. If the inlet is aligned with the chamber centre then there is no change of direction. Probably below centre is more accurate, as the outlet will tend to pull the overall flow downwards.

What I think is critical, is the height of the outlet relative to the flow centre or indirectly, to the baffle. Every build will have a slightly different flow, so any numbers provided can only be considered a starting guide. You will have to adjust or tune the height to find the most efficiency.

Dave