Dust extraction / cyclone pressure release valve

[MattRoberts]

EDIT - **** AES has posted details of an automatic design later in this thread ****


So we were discussing the issue of when shop vacs with cyclones get blocked, it creates a huge amount of pressure on the system. This will cause the weakest component to implode, which usually means the container that the dust is falling in to.

You can create a simple pressure release valve which will trigger when the pressure inside the container gets too much. I can't take credit for this I got the idea from Peter Parfett. This is a pretty simple solution though.

Get a bit of plastic pipe around 40mm in diameter, and cut a 20mm slice off the end. Next, make a cut in this slice with a saw. Now cut a hole into the lid of your dust container, but make it a slightly smaller diameter than your pipe. This will ensure the slice of pipe is a snug fit in the hole.

All you need then is to cut a couple of small bits of wood. One will be the cap, so it needs to be wider than the pipe. The other needs to be a bar shape, so when it sits on top of the other end of the pipe it still allows air to flow through.

Epoxy a bit of metal to the cap piece (or even better, use a metal lid as the cap).

I connected mine using a few cable ties, threading one through a magnet (you can get countersunk magnets which have holes in them). Our you could just epoxy a magnet to the bar piece.

That's about it. When the pressure is too much for the magnet to hold the cap, it pops off. After fixing the blockage, the slack in the purple cable tie allows you to yank the cap back on without having to open the container of even switch off the vac.

 

[Steve Maskery]

Thank you very much. I wish I'd read that a fortnight ago.

 

[AES]

Thanks Matt. Bookmarked.

AES

 

[Alexam]

Great idea Matt. It prompted me to look at Peter Parfit's video, which shows just what you have done.
http://cyclonecentral.co.uk/AssemblyInstructions/

 

[pike]

Thanks Matt,

Slightly older thread but I'm wondering when are pressure valves needed? Are they for small hose HPLV (vac) or large hose HVLP (chip extractors)? Or both? I've read contradictory comments on which one needs it. I thought it would only be the vac as they are higher pressure?

I see this one is for your vac. Did you bother for your large 100mm extractor thien container?

Cheers,
Carl.

 

[sunnybob]

If you just have a vacuum machine and the hose that came with it, theres no need for anything else.
If you start fitting cyclones and dust pails into the system, if the hose blocks the weakest link will collapse. Thats usually the bucket.

Calling it a pressure valve is misleading, its an anti suction valve. Pressure valves stop things blowing up (very dangerous) an anti suction valve stops things imploding, possibly spectacular, but not so dangerous.

But its one of those things that is not needed on most systems. If you watch peter's video, he has a large plastic cyclone to protect. Thats a couple hundred quid's worth. If youre using an old paint bucket, big deal.

Also, when a hose blocks, the vacuum noise increases alarmingly and in 99% of cases you are near enough to a kill switch to stop anything imploding.

 

[pike]

Hi sunnybob, I'm in the process of setting up cyclones for both my vac and my HVLP chip collector, so I'm wondering which one needs the valve.

The vac separator container is a metal drum. The chip cyclone is going to be one of those big blue barrels people tend to use from amazon/ebay.

 

[MattRoberts]

You need to consider the weakest point of your extraction system, as that is what will implode if there is a blockage. If your weakest point is a cloth bag, you don't need a pressure relief valve. If your weakest point is a plastic container or thin plastic cyclone, you probably do

 

[pike]

I read somewhere that High volume low pressure (chip extractor) hasn't got the pressure to implode something? I suppose the weakest point on my chip extractor would be the plastic bag or the filter cartridge?

I understand blockages can cause a container to collapse but have a few things I'm not too sure about:

1. Is a metal drum for a vac cyclone strong enough to mean I don't need the valve?
2. Do I need a valve for a chip extractor (using a plastic drum, a plastic bag and a filter cartridge)?

 

[pike]

Just reread your comment Matt and realise "waist" point shouldve said "weakest"

So I suppose my chip extractor probably won't need a valve (as there is a plastic bag and low pressure involved) and my vac cyclone might do (as it's high pressure), but might not as I'm using a metal drum for that?

 

[AES]

FWIW gents, I've just been rigging up a cyclone to go with my shop vac (a Karcher which sucks very well, but which is annoying-ly loud).

Following advice here I specially bought a metal dustbin. OK, it's a cheapo, and the basic material (galvanised sheet steel) is only about a quarter mil thick (about 32 SWG). But although it does have various stiffening rings and grooves pressed into it I can assure you that if the gets hose blocked then it does definitely suck well enough distort the sides of the bin - quite a bit actually - I haven't been able to knock all the "dents" out with a heavy rubber mallet!

Being one who likes to "re-invent the wheel" I've designed my own valve (set into the lid of the dustbin), and FWIW I call it a pressure relief valve. The difference with mine is that it resets itself automatically as soon as the hose blockage is cleared - so no stopping the vac, clearing the hose, and then re-setting the valve before you can start again.

As is my wont, it's more complicated than it needs to be, but as I've been away from the shop and the PC on health grounds it was at least something I could sketch out while laid up in bed and a chair.

I've got some pix and an (over-complicated) drawing which I'll post within the next few days just in case anyone's interested.

AES

 

[pike]

Cheers AES. I think a few people have also posted pics of diy valves. I read on another forum it's a good idea to put it in a connector/hose above the cyclone itself.

I want to avoid having one unless I really need it. I'd like to believe my chip extractor doesn't need one. Although my vac setup is a single plastic piece cyclone (not a thin plastic sheet diy thing) and I'm using a proper metal drum, I suspect I should have a valve for it as the vac is powerful. I'd be happy to just buy one if it was say a tenner.

 

[Terry - Somerset]

The numbers are a bit old school - but....

A drum 30" high by 18" diameter will have a surface area of 2200 sq inches including sides top and bottom. A 1 PSI difference is equal to 10 large blokes squashing it - albeit not all in one place. I'm also not sure at what pressure difference the fan will actually stall - so pressure difference would not increase indefinitely.

It is little surprise that even small pressure differences can implode dustbins!!.

 

[graduate_owner]

I like this idea so I am making a reply so that I can find it easily. I don't know how to bookmark.

K

 

[NazNomad]

I like this idea so I am making a reply so that I can find it easily. I don't know how to bookmark.

PM'd you the link to this thread so you don't lose it. :-D

 

[AES]

@graduate owner:

If you go to the very top LH side of this page (or any other page for that matter) you'll see a couple of little white boxes ("Post reply", etc).

1 row below that you'll see a horizontal blue line across the whole page width. That's divided into several boxes on which you can click with the mouse. One of those is called "Bookmark". You click on that and then you'll find a list of all the threads/topics you've bookmarked in your private profile page. That way you can find the stuff you're interested in again easily.

At least, that's how it looks n works on my PC setup - "your mileage may ...... "

I'll be posting details of my auto pressure relief valve soon. I'll add it to this thread.

 

[MattRoberts]

Just reread your comment Matt and realise "waist" point shouldve said "weakest"

So I suppose my chip extractor probably won't need a valve (as there is a plastic bag and low pressure involved) and my vac cyclone might do (as it's high pressure), but might not as I'm using a metal drum for that?

Hah, whoops. Correct, your chip extractor will implode the bag before anything else.

Your vac setup doesn't sound like it needs one, but if there is a blockage and you don't realise for a while, it could put a lot of strain on the motor

 

[MattRoberts]

I'll be posting details of my auto pressure relief valve soon. I'll add it to this thread.

Look forward to seeing it!

 

[AES]

Edited to delete duplicate post & 1st 2 pix.

AES

 

[AES]

Well, here goes Matt.

As said, I'm slowly doing something about dust in my cellar workshop (it's shared with the resident domestic authority!) so I bought a cyclone extractor from Steve Maskery of this parish earlier this year.

There's no doubt that I just like "complicated" (but hopefully also "elegant") solutions sometimes - Whatever floats yer boat, and all that .......... So I thought that if I was going to need a pressure relief valve in my DE system, then I wanted one that I would not have to re-set manually after every vac hose blockage

And my other excuse for this thing below is that while recently unable to do much at all in either the cellar or on my PC for health reasons, I was at least able to sit & lie about thinking & sketching all sorts of weird and wonderful ideas.

Following the advice from Steve and others here, I bought a steel dustbin especially to go with his cyclone. But after the first run without a valve it was clear that even with a dustbin rather than a plastic bucket collector, the setup would need a pressure relief valve for when the hose gets blocked - it's a thin gauge sheet galvanised steel dustbin with various stiffeners pressed into it, but when I tried a quick hose blockage as a test the dustbin walls deformed quite dramatically.

So here's my take on a DIY pressure relief valve which automatically re-sets itself to the closed position as soon as a vac hose blockage is cleared:

It's based on a plastic rainwater goods 75mm/50mm reducer, in the centre of which is mounted a moving valve stem and seal arrangement. The valve seats against the inner (sloping) walls of the reducer, and with the thin expanded PVC packaging material that I used on the ply valve head it seals very well.

The valve is retained in the closed position by a combination of a rare earth magnet and a compression spring. The magnet acts against the bottom of a 15mm square steel tube which also acts as the centre bearing support for the valve head itself and the valve stem. The compression spring acts against the top of that same tube.

The support tube is retained by a plastic ring with an internal rubber "O" ring, which was cut from a plastic rainwater pipe with integral in-line joiner. This plastic retainer also acts as a "lock" to hold the main body of the valve tight against the underside of the dustbin lid.

When a hose blockage occurs the force of the suction overcomes the power of both the magnet and the spring, so opening the system to atmosphere through the holes drilled into the main valve body below the level of the dustbin lid. This prevents the "implosion" of the weakest link in the chain - as above, in my case it's the metal dustbin.

But as soon as the hose is unblocked again the power of the compression spring overcomes the pressure of the air passing through the valve body. This closes the valve again and it's then held closed by the power of the magnet against the support tube until the next time the hose gets blocked.

The pix below illustrate it well I hope. BTW, the holes shown drilled into the lower valve support and into the main body in the pix are shown before I tested the hose blocked-valve open action. As shown in the pix these holes are too small to allow the valve function fully. But the over-elaborate coloured sketch (well, I had nothing better to do except think about back ache!!!!) does show the holes as I later enlarged them to allow the valve to open fully.

I hope this may be of interest.

Now here's the sketch (coloured so it will hopefully be clearer at this small size).

Sorry, I've just read that the max number of attachments are 10 so I'll finish off this post with the sketch and its Legend in a moment.

AES