dust to fume extractor

[wheresmejumper]

i have been thinking about fume extraction in the garage for a while now,and today picked up a dust extraction unit mega cheap,so im gona try to modify it to suit my needs.
this clarke is like one i have

i know its meant for a different purpose,but it was cheap and it sucks.
the question is what diameter pipe to use.4 inch inlet and outlet on fan.the inlet will be short and 4 inch.do i keep outlet 4 inch ducting also?it will be about 5 meters long.4 inch will be the easiest to route,as i have flexi pipe that diameter,but i also have 2,4 and 6 inch rigid pvc pipe,it would be more time consuming but if going bigger or smaller diameter than the fan outlet will help it draw more efficiently then itd be worth the extra effort?

 

[wheresmejumper]

or should i build system the opposite way round,the fan near the wall/exit,with a long inlet?

 

[rtbcomp]

Use a long inlet so it sucks in at any leaks, if you use a long outlet then dust will get blown out at any leaks.

I built an extraction system for my blast room using one of these units and standard underground soil pipes, with a variety of rubber toilet connectors to interface the extractor with the pipework.

http://www.mig-welding.co.uk/forum/album.php?albumid=1026

I've got four bags connected to the outlet and they all inflate fully so there is plenty of air getting through.

 

[wheresmejumper]

should i keep ducting same size as inlet/outlet?

 

[brightspark]

should i keep ducting same size as inlet/outlet?

if its a 4ich fan use 4 inch pipe in and out

 

[ibrooks]

I'd argue for bigger ducting. You're not looking to create any pressure - just to shift as much air as possible so you don't want any possible restrictions.

Maybe stick with a 4-inch pipe on the intake and the only reason I'd have any length of pipe is to be able to place the opening near whatever is making the fumes - if you can move the fan close enough then keep that run short.

On the outlet the bigger the pipe the less chance there is of that having an effect on the airflow. It'll only ever shift as much as it can suck through that 4-inch inlet but if there's any sort of restriction on the outlet then the amount of air it's shifting will go down.

Iain

 

[rtbcomp]

If you use larger ducting the air speed will fall which will cause the dust to drop out. so you don't really gain anything.

 

[wheresmejumper]

i sold on the chip extractor above,and have ordered an 8 inch inline duct fan,and some 6 inch flexible ducting.ill split the ducting off in two directions to extract at 2 different points,with a basic type of flow adjuster to regulate each point

 

[rtbcomp]

Is the fan designed to handle dust? IE is the motor dustproofed?

 

[wheresmejumper]

yeah,and the motor body and impeller are removable without disconnecting ducting to clean/maintain.and there is a filter in front of it.dont expect welding fumes to kill it

 

[Mode1]

Ive got electrostatic extractors,from a submarine no less!

 

[ibrooks]

If you use larger ducting the air speed will fall which will cause the dust to drop out. so you don't really gain anything.

Granted but he specified that he was using it for fume extraction and not dust extraction so keeping the air speed up doesn't matter - just volume.

Academic now since he's changed it.

 

[wheresmejumper]

got it setup,temporarily anyway.just one extraction point for now.
was trying to decide where to vent it until one of my my goats kicked a fairly round hole in a pane of glass
turned to
budget build so i used bits of galv pipe and tapering flower pots as reducers to go from 200mm fan to 150mm flex ducting.galvoband for a couple of hangers.duct tape.lots of.
begrudgingly bought a new sheet of 1.5mm ally for hood.
electricitywise its fairly efficient,120 watts but moves more air than the 1HP dust exctractor i originally had set up.