DYI fume extractor ideas

[BukitCase]

I have a good example of a fixed displacement pump laying under a workbench in pieces - got in a hurry plumbing in a hydraulic drive sickle bar cutter, forgot that the first pressure relief on a 580B is part of the loader valve. Hooked the cutter up AHEAD of the loader valve - encountered a bit tougher limb than the cutter liked and it stalled out - heard a bang, made an oily spot on the ground, discovered the center section of the gear pump was in 2 halves...

But you're right, fans act a LOT different than fixed displacement pumps - up to the point where the ducting a fan is blowing thru allows more air than the fan's open CFM rating, a larger duct will let more air (CFM) thru. The air VELOCITY would likely be faster thru the smaller piping, but NOT enough to maintain CFM (IIRC)

Ignoring the flow resistance of whatever ducting/piping due to friction/air drag, the cross-sectional area of the duct will (more or less) decide the flow. Staying below the fan's CFM ability, the CFM will closely follow the cross section of the duct (ratio wise)

With a fixed/positive displacement pump, if you start shrinking the plumbing you better do it with stronger piping or add a relief valve, or SOMETHING's gonna go pop...

In Gene's case, staying with the 6" ductwork will flow more air than 4, with a LOWER VELOCITY - perfect for NOT sucking all the shielding gas away from the weld... Steve

 

[GeneV]

Gene, pics please of your set up when you get a chance.

For sure man, I'm hoping to wrap this up tomorrow and post pics of it all done.

 

[Gordon Gould]

For sure man, I'm hoping to wrap this up tomorrow and post pics of it all done.

I know this is asking a lot but a video of you welding would really show how it works

gg

 

[GeneV]

Gene, good choice staying with the 6" - the area of a 6" circle is 28 square inches, area of a 4" circle is 12.5 square inches. Necking down to 4" basically just slowed your flow rate to 44% of what it was with straight 6" run, the velocity (as you discovered) suffers. Depending on your inline fan, necking down might've ALSO shortened the life of the fan motor.

No "internet expert" here, just 33 years in industrial instrumentation preceeded by another 15 in electronics... Steve

Also no expert, most of my knowledge of fluid dynamics is based on fixed displacement pumps. And that knowledge leads to me expect that when you neck a pipe down (ex from 6" to 4") the velocity will increase, not decrease. The same volume of medium flowing through a smaller pipe must flow faster in order for the volume to be the same. I guess a fan in a tube behaves differently. In my mind, volume must the variable here instead of velocity; going from 6" to 4 inches must decrease the volume by the percentage you figured, with velocity remaining constant, no? Or is the whole equation thrown out of whack by changing pipe diameter?

Guys, that's also what I was reading about velocity increases with a downsized pipe. This was one of the pages I was looking at when researching this: What Happens to Air Flow in Ducts When Size Changes? | Energy Vanguard

I'm glad I initially bought both the straight 6" duct and a reducer with 4" duct. So again, intake is 6", fan is 6", and then came the decision on what to put downstream of that, ie, 6" or 4" exhaust.

I devised a 2-part test to see what works better. First I stood in front of the intake with a piece of paper, slowly moving it toward the intake until the paper would start bending toward it with the suction. I had to get a little closer to the intake with the 4" than I did with the 6". Noticeable, but didn't seem all that dramatic.

But where I really noticed a difference was at the other end, the exhaust. When I stood in front of it, the 4" exhaust was like a decent breeze against my t-shirt. With the 6", it was way stronger flow, it was flapping my shirt pretty good.

 

[GeneV]

I know this is asking a lot but a video of you welding would really show how it works

gg

Yeh absolutely, will do.

 

[Gordon Gould]

We made up 3 of these in our weld shop at work using the MonkeyArms on the end. That allowed quite a large radius of coverage:

Looking at that second picture they seem to work pretty well - how are they working?? Those vortex duct fans look like great units. On a different level than HF for sure but still cheaper than factory made welding fume extractor.

gg

 

[GeneV]

We made up 3 of these in our weld shop at work using the MonkeyArms on the end. That allowed quite a large radius of coverage:

That's a real nice setup!

 

[chim]

Looking at that second picture they seem to work pretty well - how are they working?? Those vortex duct fans look like great units. On a different level than HF for sure but still cheaper than factory made welding fume extractor.

gg

They work very well and although I don't recall the costs, it was worth spending some money to improve the air quality. Our existing exhaust fans (think "whole house fans" only commercial sized) didn't work as well. The sound of the Vortex fans is almost undetectable with the presence of other sounds in the shop. The guys like them.

This was an in-house project. I checked with a couple of our regular vendors and they didn't have anything reasonably priced. After some online research, I ordered a fan and the first Monkey Arm. The parts sat around for the best part of a year until we hit such a lull that there was very little else to do but build the prototype. Did I mention there was some reluctance to trying it out?

The mounting for that one had one stiff arm mounted to a column with a homebrew pipe-in-pipe hinge, and all the adjustment was via the Monkey Arm mechanism. We needed a greater range because some of the welding is done on a large heavy table at the station, and some is out in front of the table when it involves large pieces or powered rollers. We modified the arm by adding a hinge in the middle and making the arm longer overall.

Shortly after we finalized the design for that one and the men saw how it worked, they were ready for two more.

 

[jaxs]

So ya'll want to build something that sucks. You can buy new material and build better for less than welding shops sell but with a little legwork,you can build one for peanuts that does a better job than store bought. You can try buying salvage from a contractor but I suggest making friends with the people at local scrap metal recyling yard and give them a list of what you need. About 50% of material I use is from a yard not far from me. Cold drinks and snacks are appreciated on triple digit summer days.
We will start with a basic unit to handle welding fumes then move on to another that is A low noise B doesn't waste heated shop air in winter C bring's outside air in summer to replace hot shop air D Filter's air in woodshop E Evacs paint fumes without starting a fire.
Start with the clamshell from a 75k or less furnace or 24k or less cooling air handler. 95% of fossil fuei furnaces will have 120 volt motor. 100% of electric heat units will have 240v motor. Both will have 2 to 4 speeds. Next you need a start or take-off collar. Grab one that will cover hole on side of clamshell. If duct size is too large you might have to buy an inexpensive reducer at big box, plumbing supply or sheet metal shop. Hvac supply houses are getting to where they refuse selling to public. You can set blower in a window or door. If you would rather run duct through wall, cover blower discharge and use another start collar or a register boot can easily adapt to blower discharge. This thing may have more suction than you prefer but there's solutions. If you are lucky,you might find an adjustable dampered start collar at scrap yard. They cost about $30 new. With a couple of start collars.you can cobble up a box with sliding damper between blower and work table. A square box with sliding "gate" is far easier to build than a flip damper. All this doesn't have to be leak free,there's plenty of reserve air power to spare a few leaks. Install wheels on blower or make other improvements to suit you taste.
The blower for delux version is a little difficult to find. Here's a visual for the type you need http://://www.amazon.com/Broan-Motor-Assembly/dp/B01IW67TX4/ref=pd_rhf_se_p_img_2?_encoding=UTF8&psc=1&refRID=W2QYBBWFGBSKM8Y5HSKJ
A radial blade (squirrel cage) is much quiter and develop's mor pressure than axial (propeller blade) fan. A range blower like the example above will move 300 to 500 cfm which is ideal for welding fumes. The same configuration capiable of larger volume is found in ceiling mount appartment hvac evaporators,a few window acs. Again,these will have multiple speeds and come with both 120v and 240v motors. Set up is much the same as basic unit except we have two different air paths. Additionally,we seal fan housings between motor and fan blades so that incoming paint fumes never pass through motor windings where it might be ignighted. Sealing housing to force all intake through ducts also prevent's sucking heated shop air. You can cut and notch sheetmetal to slide over motor shaft and fasten to housing. To prevent losing heated air from shop,one fan pull's outdoor air through duct and discharge's near work where it is mixed with smoke and pulled through other duct and fan then discharged outdoors. With a little tweeking, far less shop air is evacuated than if using our origional design.
To filter air,build a box with 8 or better Merv hvac filter. Hook suction duct to box. If desired,discharge duct can be positioned blowing on your back so that dirty air is push away by clean filtered air.
Well there you go,have fun,breath easy and stay healthy.

 

[Fallon]

On a semi-related note... If you are building a dust collector you need to keep the velocity up, not just the CFM. A high velocity keeps the dust & dirt from falling out of the airflow & plugging the pipe. Not so much relevant to a fume extractor though.