Another Laser Exhaust Question

[Brian Leavitt]

Howdy Fellas,
Reading another recent post about exhaust got me wondering about stuff...

We are moving in a couple of months and this gives me a good opportunity to upgrade my exhaust system to something with more appropriate airflow. The problem is I have no clue how to calculate this all out, so maybe you all can help with this.

The basic setup will have to remain as I have it now except for two things. I can run a larger main pipe, if needed, and the blower can/will be larger. What I have now is all three lasers being exhausted by a single, roof-mounted blower. All three lasers have two 4" exhaust holes and all are attached to "Y" pipes coming off the main 6" rigid pipe. This 6" pipe goes up 24 feet and then over 10 feet where it exits the roof. Apparently the regulations here require that the blower be at least 10 feet from the edge of the roof.

The Universal books state that 500cfm at 6" sp is required. The Epilog book states that 650 cfm is required, but doesn't state at what sp. So that's two lasers requiring 500 cfm @ 6" sp, and one requiring 650 cfm @ unknown sp. Combined, that's 1650 cfm, but I don't know if it's that simple when looking at blower ratings - especially considering the distance from the lasers to the blower.

I need to keep exhausting all three with a single blower, but I don't know what to get. There is still going to be 34-40 feet of pipe between the lasers and blower at the new place, but I can increase the size of the pipe if needed. Is this enough info for anyone to offer a suggestion on a blower?

Thanks,
B

[Dave Sheldrake]

The blower ratings are given as at the exit or gross flow Much like compressors give CFM displacement (when what matters is FAD(Free Air Delivered) ie: how much air AT pressure. What the SP figure will give is how much resistance to flow the blower will provide so the CFM isn't as important as knowing what SP losses are involved

The pipework is going to suck efficiency...a 90 degree 6 inch elbow for example has the same gross loss at 12 feet of straight pipe

[Keith Winter]

I'm not sure about mounting to the roof, but as far as blower suggestions I'm very happy with my shop fox 3 hp blower. My run is pretty long about 20" on the in side and 25 feet on the out, and it has plenty of suction for 3 mid to larger sized lasers, and could likely even work for a 4th in a pinch but I haven't tested a 4th. Suction is extremely good and the output is wicked powerful. You could mount at the floor if you so chose and easily push the air up and out 40' with a lot of force left. (though many will advise you to mount outside for sound and a sealed intake only system if possible) Go 8“ on your main line and don't look back. Solid duct pipe screw and metal lined tape everything, even tape the joints in the elbows. You'll be surprised the cumulative difference it makes.

[Brian Leavitt]

Thanks, fellas. Keith - would you happen to have a model # on that Shop Fox unit? I'd like to look in to that further, but the only ones I'm seeing come set up to use dust collection bags.

[Keith Winter]

Thanks, fellas. Keith - would you happen to have a model # on that Shop Fox unit? I'd like to look in to that further, but the only ones I'm seeing come set up to use dust collection bags.

Yeap that's it Brian!

SHOP FOX W1687 3-Horsepower 2,800 CFM Dust Collector is what I have. Throw away the bags (or sell them on craigslist). Had an basic size adapter made to take the outbound square port to a 6" round port by a local sheet metal company. Rest is right out of the box, great machine, I love it.

[Brian Leavitt]

Thanks again, Keith. I'm going to give that one some serious thought.