One Big Blower Versus Two Small Blowers

Two small blowers that can run independently or together may be a more economical and more effective dust collection setup. December 6, 2006

I am faced with the challenge of installing a baghouse with a 75HP blower and three air locks. The used system was purchased to replace a 30-HP cyclone system with a single air lock. The mill has two 6-head molders, two rip/gang saws, a couple of sanders, planers, and shapers; all on (about) a 100 ft run with continuously decreasing trunk sizes. We aren't getting enough suction to run both molders at the same time. The new system (bought used) is sitting outside on its cement pads and steel platform, but it needs its 3-23 inch inlets piped into the building to the machines and its 3-23 inch outlets piped back into the building to replace the air removed from the building.

I'm concerned that the cost of installing this system and its increased energy costs may outweigh the added chip removal benefits. Although it would be attractive to double molder capacity, am I undertaking a huge engineering project and increased runtime costs where the 30-HP system may be adequate and just improperly engineered? Or perhaps a second 30-HP system would be more prudent? Then I could shut one off if one of the moulders isn't running.

Forum Responses
(Dust Collection and Safety Equipment Forum)
From contributor D:
The 75 hp will give you a spike in electric use, which will become the multiplier used to calculate your electric bill. This spike you don't want. I would suggest improving your current system, its piping and blast gate applications.

The idea of a separate collector for the molders is good. They may also be relocated closer to the main trunk. I ran a 60hp Nordfab system for years and its cost in electricity pissed me each month! In my opinion, the smaller, the better and more well-engineered. Having two small units where one is off, one is on, is a good idea, or multiple blowers on same line where they can be turned on as needed. Maybe one dedicated to the problem machines? I would rather sweep the floor than pay those large profit-eating electric bills! Having two or three blowers on the same line is a popular thing these days; bring them on line only as needed. Think it out and try to avoid those large motors.

From contributor G:
If the 75 hp system is waiting outside, it seems a little late to ask these questions now. Are two 30hp systems still an option?

From the original questioner:

It's never too late to save significant runtime costs! I'm exploring alternatives before sinking additional capital into finishing this large project. Yes, 2-30 HP systems is an option. I'm also intrigued by the inline blowers mentioned above. May I call them "boosters"? Is it doable to put a booster blower in the branch line (in front of each molder manifold) and let it output into the main trunk? I like this idea if it will work because I can switch it on and off with the moulder to which it is dedicated.

From contributor R:
Be careful with booster fans into the main line. You will have to monitor the amps on the main blower. Better to use two fans to blow into the receiving filter unit. Mount back draft dampers on inlets so the fans can be run independently. Your 6 head molders can be put on one line or separated for shop production needs. The manifolds need to be at least 14" diameter for a six head molder if all 6" outlets. What type of used equipment did you purchase? Your pipe design did not sound right; the 30hp with cyclone may be adequate, but poor piping design.

From the original questioner:
The system to be installed is Wheelibrator. It was already here; that is, I did not purchase it. I'm not sure who makes the present system. I climbed up on the tower, but couldn't find a name. It has a 30 hp blower that dumps into a cyclone shaped hopper that in turn feeds a 5-hp air lock. Here is a not-to-scale pipe diagram.

Click here for higher quality, full size image

From contributor R:
The Wheelabrator mentioned is an outdated unit and not very efficient to operate. It was used a lot in other industries. The new reverse jet and pulse jet units are more efficient. Dust systems are designed by machine outlet size in square inches converted to square feet with all added together for a total size of the mainline. Your main at the fan is 18" or 254 sq. in. If all your outlets are open, you equal 506 sq. in. or about a 25" pipe. Most systems for wood are sized using 4000 to 5000 fpm carrying velocity (speed of air in the pipe) and most systems with a main receiving filter or after filter will have a minimum of 12" - 15" of static resistance in the system. For example, 26" inlet fan @ 5000 fpm @ 12" of static BHP would be 66.36 or would require a 75 hp motor.

You sort of have a couple of things working against you:
1. Old outdated filter (parts?).
2. Main piping that will have to be completely changed even for two molders to run together.
3. High cost of operation in long term.

From contributor N:
Something that can reduce the cost of any dust collection system is motor starters to ramp the motors up to speed rather than letting them draw full starting amps. This lowers your demand meter setting. Also, variable fan speed, which is set by the air velocity and static pressure in your system. I do not know about the availability on retrofits, but Disa (now Dantherm) has them as an option on a new system. There are others as well that offer this system. I would bet if you calculated the cost of having an employee sweep up shavings, and the potential of lower quality millwork due to poor extraction, the electric and/or a new system may seem cheap in comparison.