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22nd September 2019, 01:19 PM #1GOLD MEMBER
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Shop vac cyclone really inefficient
My cyclone used to run pretty good. I had it attached to a 15 or 20L pale/plastic bucket but they kept on collapsing under vac pressure so I decided to build a ply box. Most of the dust used to end up in the bucket, even much of the really fine dust from the sander.
For whatever reason with the ply box almost all of it goes straight into the vac and not into the ply box! I can't work out why.
All the old plastic buckets I used I could never get a good seal between the cyclone and the plastic bucket as the lid never really stuck to the silicon. With the ply box I probably have the best seal I've ever achieved. Could that be the reason? The system is too sealed?
The ply box is also about 3x bigger then the bucket - could that be a reason?
I've also 3d printed these adapters which thread onto the vac hose and fits perfect onto the cyclone. When I used to use tape there was some leaking but it seemed to work. Again too good of a seal?
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22nd September 2019 01:19 PM # ADSGoogle Adsense Advertisement
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22nd September 2019, 01:22 PM #2GOLD MEMBER
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Do you have the hoses on the cyclone around the right way?
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22nd September 2019, 01:42 PM #3.
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The system CANNOT be two too sealed, if anything its the other way around.
The first thing I would think of in these situations is the box has a small leak, it only needs to be a tiny leak and it will defeat the cyclone operation.
Are you absolutely sure about the air tightness of the box?
If you had a suitable vac gauge I would say attach it to the Vac alone and then the box with the vac attached. If the box plus vac vacuum is lower than the vac alone vacuum then there is a leak.
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22nd September 2019, 01:50 PM #4GOLD MEMBER
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Hoses are correct.
Its possible there is air leak. The ply I used was from an old crate but I went around filling holes. Maybe I did a crap job.
What I initially thought was that the dust was not cycling down the vortex and getting sucked up by the vac at the top before it could go down.
Thoughts on putting the hose like this (looking from the underside of the lid)
I'll try build a new one
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22nd September 2019, 02:00 PM #5.
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If you can get a vacuum only seal (ie no actual physical connection) between the running vac and the box you should be able to lift the box off the ground using vacuum only - if not then you have a leak.
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22nd September 2019, 02:18 PM #6GOLD MEMBER
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That dark hose would completely stop any cyclone action and result in the dust being stired up and sucked out of the bottom container.
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22nd September 2019, 02:37 PM #7Woodworking mechanic
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Try putting a large radius on the timber lid where the cyclone attaches so the opening gets wider as it goes into the box. The lid is quite thick and the straight sides could be disturbing the air flow.
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22nd September 2019, 04:03 PM #8GOLD MEMBER
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Lappa's suggestion is a good place to start, thick lids have been known to cause significant disruption to the airflow with these cyclones, so take to the debris port in the lid with a large radius roundover bit. Also, at the inlet port into the cyclone you need to have the hose back from the cyclone body, 30mm should be enough. From your last pic. it looks like you don't have any effective location of the hose in your connector, if it's not properly restrained it'll get sucked into the body of the cyclone and the resultant disruption of the airflow will totally compromise it's operation.
A small leak, and I'm assuming it could only be small or you'd definitely know about it, in the container you've built is unlikely to result in what you're seeing, although if there is a leak at the base of the box it would certainly have an effect.
If those fixes don't work get yourself a 15 or 20 litre ring lock paint tin, they really are the best collection containers for these.
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22nd September 2019, 08:03 PM #9SENIOR MEMBER
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I use the Oneida Dust Deputy kit - expensive but works well without having to play around with DIY. They use two buckets (one inside the other) and I've never had a problem with it collapsing. Maybe the vacuum (Detroit brand from Total Tools) isn't strong enough. The only issue (operator error) I've had with them is the dust fills up in the bucket and I haven't noticed, so it flows into the vacuum and clogs the filter.
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22nd September 2019, 08:31 PM #10GOLD MEMBER
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There can only be one reason a bucket would collapse and that is there is not enough air being allowed in. If it was steel for instance that would not matter but being plastic it does.
CHRIS
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22nd September 2019, 08:42 PM #11
I just reinforced the bucket with plywood ribs and screwed them on like so.
IMG_0179.jpg
Almost 100% of the dust goes in the bucket. I would just go back to the bucket if I were you.
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23rd September 2019, 02:21 PM #12
I use a 40L plastic drum and it only sucks flat if the suction air is blocked. I got a small cyclone to put on top but that actually reduced its efficiency and I also got more dust in the vac. I went back to using the drum on it's own.
Regards
John
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23rd September 2019, 02:56 PM #13GOLD MEMBER
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23rd September 2019, 04:23 PM #14Senior Member
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Two common primary dust extraction methods accompanying vacuum suction are:
1. Cyclone
2. Settling drum.
They are both using the difference in weight between dust and air to seperate the dust out.
The cyclone spins air in a circular motion which forces the heavy dust to the outside of the chamber and down the bottom of the cyclone outlet, relatively clean air should exit the top of the cyclone.
Centrifugal forces generated by the spinning motion are many times higher than gravity so you can separate finer dust with a smaller piece of equipment.
Given the driving force is a vacuum sealing the bottom is important. If you let air in through the bottom it will stuff up the air flow path, preventing the heavy particles from dropping out the bottom. Other reasons for poor performance include:
The cyclone is too small for your application. (probably not if used successfully before on same duty)
The inlet pipe isnt properly tangential to the barrel of the cyclone.
A Settling drum is one where you try to slow down the air inside it to allow time for the dust to fall out. Gravity does the separation and dust falls to the bottom. You need a larger container and typically the inlet and outlets are on opposite sides of the container. 40L bins are good for this, 80L ones even better if you can really slow down the air. It's been too long since University for met o remember good air speed figures for separation in these conditions and my design books are packed away.
If you want to get really fancy an Electrostatic Precipitator is pretty cool as are water misting sprays but far outside any useful application in this forum and are stuck after the primary separation stage. Most normal operators use a standard filter for that.
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24th September 2019, 09:51 PM #15
Hi gwertyu
It basically uses the round drum body as the cyclone. Hose to vac is in the center of the lid and the pickup hose goes in near the side of the lid to deflect shavings on to the side of the drum so it swirls around.
I used it that way for about 10 years then tried a small cyclone on top. The cyclone reduced the performance quite a bit so I went back to the drum as you see it in the pictures. The vac is 1100w. I think more power would be needed for the cyclone to work well.
Regards
John
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