View Full Version : In line Fan

Walt Langhans
03-31-2013, 8:49 AM
I'm looking at getting an in line fan to replace the one I currently have to help reduce the noise in the shop. I found a 6 inch one that looks pretty good and has a CFM rating of 250. How do I know if that's going to be enough for my laser? And if it's not and I get 2 does that mean that I'll have a CFM rating of 500?


Mike Null
03-31-2013, 9:04 AM

That's about the size of my unit-mine may be 300 cfm. Two won't help you.

What you need to consider is the length of the run and the number of els or bends in the line. Each bend consumes efficiency of the unit as does a long run. The good thing is that most in-line blowers are at least 6" in diameter which means that you will probably be using a reducer to a 4" fitting at the engraver and possibly at the exit point. That seems to improve the performance.

I did considerable research on this before I bought the inline and found that most engineers can't agree on what it takes to determine your needs.

Joe Pelonio
03-31-2013, 9:11 AM
Check your manual for the requirement, mine is minimum 400 CFM. When I had it in a place with a 25' run, mostly straight, I used an 800 CFM blower.

Mike Lassiter
03-31-2013, 9:34 AM
We have a ULS ILS series with 24x48 inch table. ULS manual called for min. of 1100 cfm. I got a dust collector from Penn State I think rated at 1800 cfm (3.5 HP 240v motor) and ran 6" duct work from laser to blower which is mounted inside a "closet" and the air is then returned back into the building at the other end of the 32' building. I built the room for the blower and insulated the walls and ceiling for noise control. I have way more than the minimum flow and it seems to me having more than the minimum has benefits. I have a remote wireless control that I use to turn the blower on & off. I have watched sheet material actually be sucked down to the table when the blower comes on. We also have a "traveling exhaust" on our laser so when I am cutting I lay paper on cutting grid to minimise air flow thru the unused area of the cutting table. The suction pulls sheet goods down to the cutting table and helps eliminate warped material not laying flat.
I am very pleased with how well our systems works. I would consider more than minimum required cfm if possible. While minimum may work, it maybe marginal. I rarely have need to clean the lens, which I believe is due to superior smoke extraction inside the cabinet.

Walt Langhans
03-31-2013, 9:47 AM
Two won't help you.

I was afraid of that.

most engineers can't agree on what it takes to determine your needs.

Well that's kind of disturbing, and I thought it was economists that could never agree, lol. The fan I have now works great, but there is nothing that gives me any ratings is there any way I can measure what I'm using now?

Check your manual for the requirement,

I have a manual, lol. Yeah... it was pretty much useless for this, just had a picture of the fan and said to attach it to the machine. Ahhh simplicity... :D

Richard Rumancik
03-31-2013, 12:30 PM
. . . I found a 6 inch one that looks pretty good and has a CFM rating of 250. How do I know if that's going to be enough for my laser? And if it's not and I get 2 does that mean that I'll have a CFM rating of 500? . . .

If the manufacturer did not make a recommendation for a blower then it is up to you to decide how much is "enough". Perhaps that is why Mike feels that engineers can't agree . . . on what basis will you decide? If the question is posed precisely there will be a better chance of a consistent answer. You need to clear the smoke of course but if you are cutting balsa or marking with Cermark the requirements may be different than if you are doing heavy duty cutting.

But a blower rated for 250 cfm has to have another parameter with it for it to be useful info - which is the static pressure. (It's kind of like how an engine is rated for horsepower (or KW) at a certain speed.) Both parameters are needed to compare fans and blowers.

If the inline fan provides 250 cfm at 2" static pressure then if you put two in series you will get (roughly) 250 cfm at 4" static pressure. This might be a good thing to do, as it will have more energy to draw through the laser and overcome flow impedences from obstructions, ducting, elbows, flex tube etc.

The only way you will get 500 is if you put them in parallel. But that can be very difficult to achieve successfully as you have two separate paths and then you need to add dampers in case one fails. It is very easy to get unstable operating conditions. I do not recommend it.

In any case I would not put blowers in series or parallel unless they were 100% identical, or you may spend a lot of time debugging it.

Walt Langhans
03-31-2013, 4:03 PM
then it is up to you to decide how much is "enough".

Good point. I cut / engrave mostly 1/8" MDF and 1mm cardboard. I do plan of working with acrylic in the future, but I have no idea if it produces more or less smoke then the MDF. I upgraded exhaust fan to the one that Shenui sends with it's larger laser, and even with the lid open it still sucks the smoke right out. So I would like that performance or better just quieter.

Mike Lassiter
03-31-2013, 4:17 PM
if what you are now using is working good, but noisy; perhaps relocating the unit away farther from the laser,or building something to enclose it that you could insulate for sound. I would caution about totally enclosing the motor were it cannot get air to cool itself with though. It needs air to keep it cool while running and putting it in a closed box would likely cause the motor to get hot after a time running it.

walter hofmann
04-01-2013, 5:38 AM
Hi walt
I use a 500CFM 6 inch inline fan with reduction to 4 inch on both sidesfrom ebay around $80 and it works perfect. I even had to put a piece of chicken wire in front of the intake because by cutting small 1/4 plywood pieces it would suck it right out.the noice is just like a smoth wind

Walt Langhans
04-01-2013, 11:19 AM
Thanks Walt. Which model laser do you have?

Dan Hintz
04-01-2013, 6:41 PM
most engineers can't agree on what it takes to determine your needs.

My thoughts on this one...

Some are happy with removing light smoke from their machine, in which case an inline with 250CFM and relatively low static pressure is peachy. Others, such as myself, also use the fan as a vacuum source... in which case I connect it to my 2HP duct collector with 9"+ of static pressure at the same CFM as the inline. Sucks warped stuff flat!

Mike Null
04-02-2013, 4:36 AM

As you indicate--that's a whole different animal.

But it's not what I meant when I said engineers can't agree. I was absolutely exasperated after contacting various engineers including hvac people to find how little they actually knew about static pressure and cfm and how to calculate requirements given certain parameters.

walter hofmann
04-02-2013, 5:22 AM
Hi walt
I have a converted 40W and a converted older 80W. by the way the fan is a hydrophonic