Would 2 of these in-line blowers in series increase my fume extraction CFM?

[AuggieDog]

I use a blower like the one below. They are cheap, last fairly long, and are easy to source. When one goes bad it's no big deal to change it out for a new one. Can someone smarter than me (all of you) tell me if I put two in series, will it increase (or double) the amount of suction in my fume hood? I have a direct suction into a vertical pipe (was the best I can do) but currently, one fan is just a little bit inadequate. This may seem like a no brainer to most people, but I don't want to start modifying my system until I am sure.
Thanks for your help

 

[FrugalRefiner]

I use a blower like the one below. They are cheap, last fairly long, and are easy to source. When one goes bad it's no big deal to change it out for a new one. Can someone smarter than me (all of you) tell me if I put two in series, will it increase (or double) the amount of suction in my fume hood?

No. It's not that I'm smarter than you, just that I was exposed to this stuff in an old career. Adding another fan inline (I assume that's what you mean by in series) might increase the flow somewhat, but not by a lot, and definitely not double the amount.

Now, you could add a second exhaust system, just like the first system, with separate exit to the outdoors, and you might come close to doubling the amount of gas moved through your hood. It would probably be a bit less than double due to restrictions on make up air. But if you want to increase gas flow by doubling up on the fans, run them in parallel instead of in series.

Dave

 

[AuggieDog]

No. It's not that I'm smarter than you, just that I was exposed to this stuff in an old career. Adding another fan inline (I assume that's what you mean by in series) might increase the flow somewhat, but not by a lot, and definitely not double the amount.

Now, you could add a second exhaust system, just like the first system, with separate exit to the outdoors, and you might come close to doubling the amount of gas moved through your hood. It would probably be a bit less than double due to restrictions on make up air. But if you want to increase gas flow by doubling up on the fans, run them in parallel instead of in series.

Dave

Ok smarty pants
I had a feeling this was this case. Adding a second fan in parallel is quite a bit more involved in my situation. Back to the drawing board, as they say

 

[SRM]

Just a quick emphasis to what Dave said, if you decide to run a new parallel system you need a separate exhaust or a larger common exhaust. For example, if you are doubling a 4 inch system, you will need a single 6 inch exhaust.

 

[Mick Tee]

This is not my area of expertise, but I have had enough exposure to it to echo the sentiments of the previous comments. While in theory, two fans in series would increase your flow considerably, the resistance to flow through such systems increases exponentially with flowrate to the point where the extra fan could actually decrease the throughput if the existing system were on the limit. Blame fluid dynamics.

 

[GieTM]

I recently rebuilt my booth with some nice conveniences built in.
Per this topic I decided to install two 8 amp variable speed (that had to be custom) janitorial floor fans. The strange looking ones for mopping. they are made out of some everything proof material and the motors are fully protected. To me that means they last a little longer then many and are a great value. Then I then I bought 4 heavy duty plastic 4" bolt on ducting converter things, 2 clear woodworking extraction hoses 4", and installed the first port at 25" high in the booth on a tee so that the suction happens at a 90 degree angle to accommodate the spacing for 3 hot plates, or the tee can rotate 90 degrees making the lower intake at 20" high which is perfect for a large vessel. The top of the tee is at 30" which is perfect for a vigreux column.
Just that 1 fan can immediately clear a 1200W smoke machine without ever reaching the top of the hood or escaping the 28"X44" booth.
For safety, I guess, the second 4" X 8 amp fan is attached to the absolute ceiling of the booth with a plastic floor sweep attachment, also for woodworking. They are on 2 seperate circuits, separate ports and hoses. 2 redundant systems.
The exhaust fans are outside the shop in a shelter I built for them and insulated that with sound proof insulation. Total silence.
Oh yeah, i'm still experimenting with the extraction fittings but I think I like it like it is.
The one enhancement I made was adding a blast gate to the lower vent to control the magnitude of the suck. On the top I added a 2" hose to the floor sweep so that I can position it anywhere in the booth. Like if you do something that's more fumy then other stuff.
It's sorta overkill I hear, but I TOTALLY love it. I breath easy so to speak.
.....yes, I like wearing my mask too

I hope that inspires someone to clear the air.