Dust extraction

[Ruskie7]

Dear all

I am looking to put in a dust extraction system with 2 inch pvc pipe. I’ve heard myths, I have heard horror stories and somethings nothing about using pvc pipes and static charges.

I don’t want it exploding or being a fire hazard so any advice?

 

[dzj]

A lot of people use PVC. I haven't heard of anyone's shop going up in smoke because of static discharge.
Some people ground such duct work, just in case.
It's not complicated and pretty low cost, so if you're worried, why not.

 

[Inspector]

Read this. http://www.thewoodnerd.com/articles/dustExplosion.html Any sparks you get from static are just annoying but they could hurt sensitive electronic circuits like those in a CNC router or laser.

Pete

 

[sunnybob]

large commercial dust extraction systems can have problems and are almost always earthed. But the earth needs to be inside the tube to have any effect. Earthing the outside of a plastic pipe is totally pointless. (plastic insulates, yeah?)

A small home made system wont cause any troubles.
If you are going to run the pipe for more than a couple metres you need bigger pipe or you will lose too much suction through flow restriction.

I have a 5 metre run in 62 mm and thats barely adequate.

 

[Peterm1000]

I use 4 inch vent pipe - used for shower vents. I am sure it is not as tough as soil pipe, but at £6.50 for 2 metres it's an awful lot cheaper (and makes the £20 Axminster want for a 3 foot length of plastic tube look absurd). I make 90 degree bends by joining 2 45 degree bends with a short length of pipe in the middle. It fits straight over the top of blast gates. Been running about 9 metres of vent pipe (longest run) to my bandsaw with about 1.5 metres of flexible hose on the end for the last year or so on a very ordinary extractor. Works perfectly.

I don't think a 2 inch system is going to collect anything unless you have it attached to a vacuum cleaner (high pressure low volume?)

https://www.tlc-direct.co.uk/Main_Index ... index.html

 

[LBCarpentry]

If pvc ducting is an explosive fire hazard then we’re screwed.

 

[sunnybob]

In very special circumstances PVc pipe can be an explosive hazard. Material flowing along the inside causes static electricity (did you ever rub a balloon on your jumper and stick the balloon on the wall?).
If enough static builds up it can cause a spark to jump. (ever had a minor shock off of a car door handle?)
If there is an explosive mixture in the pipe (flour is a prime example) then there can be an explosion. But there are a lot of "ifs" to get to that stage.

Large commercial premises extracting large quantities of very fine sawdust can be at risk and there are documented examples of fire in those buildings. In those circumstances bare copper wire is run the entire length of the inside of the ductwork preventing static buildup.

In a small workshop or home hobby situation, the risk is so small as to be unmeasurable and I havent ever heard of a problem arising.
But if a person was paranoid, there would be nothing stopping them from running the earthing wire inside the pipe.

 

[Ruskie7]

Thank you all for the feedback and advice.

So in essence I will need a wider pipe. It isn’t going to get used a ton but if I want to earth it I could quite easily from what you saying with a copper wire in the pvc.

It’s going to be hooked up to my record power dust extractor and dust cyclone I’ve biult as I want to avoid emptying the dust collector of the Chips and dust every 5 minutes.

 

[John McM]

That’s a great price for 4” pvc. TLC will be getting a visit

 

[sunnybob]

The system has to be balanced. Theres no point using 4" pipe if the extractor has a 2" inlet. However, it is possible to use a 4" extractor and run it through narrower pipe, but its not recommended
But yes, the larger the system diameter the more dust you will capture. Keep the pipe run as short as possible, avoid 90 degree elbows and especially T pieces as much as possible as they severely restrict flow.

Truly, earthing is not a priority in a home situation, I dont know if there are any earthed home systems in the UK, but if you want to, then go ahead, it wont make any difference to the operation. But make sure you earth the pipe at BOTH ends of the run, and if youre going to run bare wire through it, make sure you have extra slack to enable you to undo a joint or two if the pipe does become blocked.

 

[Inspector]

Rather than a wire inside the pipe that can catch shavings and clog the pipe I would use the method described in Bill Pentz's site. Where metal foil tape is stuck to the inside of the pipe. It has the small benefit of not adding to the turbulence in the pipes. The aluminium tape is used a lot by the furnace guys for sealing the joints of heating/cooling ducts. If you can't find it the copper foil tape used by stained glass artists would work nicely too.

Pete