Trying to understand my Harbor Freight DC suction capacity

[Greg Urwiller]

I recently bought a HF DC for my shop. I haven't used it much yet. I plan on building a Thien top hat baffle and mounting the whole thing on a wooden frame. At this time, until I really figure out the shop layout I want to go with, I plan on rolling the DC to the tool being used. Anyway, I did use it yesterday to clean out my old table saw cabinet which had a lot of sawdust in it. The HF has a "Y" input to the blower. I happened to take the cap off the one leg of the "Y" after I sucked up a fair amount of dust (the hose was connected to the other leg), and I noticed that the dust swirling in the bag and velocity of the dust increased. Now it seems from reading the HF DC posts here that most people feel that it doesn't do any good to increase the size of the piping on the HF DC's. But isn't the increase in velocity and dust movement in the bag an indication that a larger intake is better? Also, how does the volume or area of the 2 4" legs of the "Y" relate to the 5" intake of the blower? In other words, if you went with a single 5" opening (w/o the "Y") will I get better air volume or, what's it called, static pressure? This would require 5" hose and fittings, which I'm not sure is available. I'm having a hard time grasping the principal here, and I wasn't really concerned about the specific's until I noticed the increase in air volume. Thanks. Greg

[Alan Schaffter]

5" inlet is better, but the real issue is what happens in the ducting and at the pickup end- do you have the required velocity to keep dust in suspension in the moving air and what kind of CFM do you have. You want the largest possible diam. inlet and ducting without letting the velocity drop below 2500 fpm in horizontal runs. The longer your ductwork the more static pressure resistance and the harder it is to maintain velocity. That DC is really not suitable for a ducted layout since it won't provide the required CFM needed to properly collect dust at the source.

[Phil Thien]

There are people out there using the HF unit with 5" and 6" ducted systems and having excellent luck. A couple of years ago someone sent me pics of their HF DC connected to 6" PVC pipes. He had his machines aligned down one wall of his basement. The 6" main was a straight shot over the tools, and had a wye for each of his tools. He kept the flex to less than 2-3' for each tool.

At the end was his HF DC with one of my baffles, and a cart. filter. It worked great for him.

[Greg Urwiller]

Thanks for the replies. But I'm not planning on running any ductwork, but having the DC mobile. I don't know what layout I'll go with until I use the shop for a time. So my main question concerns the apparent increase in velocity/turbulence in the DC bag when I opened both legs of the "Y". My plan was to roll the DC to the machine, hook up a length of 4" hose to one leg of the "Y", and go to work. But it appears to me that I have a fair amount more suction with both legs of the "Y" open. Does this sound right? If so, should I just uncap the other leg when working, or should I go with a 5" hose right out of the blower? And, is 5" hose even available anywhere? Of course the other thing to consider then is having to find 5" machine connections also. Thanks. Greg

[Dan Friedrichs]

. But it appears to me that I have a fair amount more suction with both legs of the "Y" open. Does this sound right?

Not really... by opening the other inlet, you are running about twice as much air through the blower and into the bag....but obviously only the air being sucked through the port that is connected to the tool is actually doing you any good, right? No, do not uncap the other port - you'll actually decrease the suction available to the hose you have attached to the tool port.

5" flex hose is available. The best solution would be to run a short piece of 5" flex directly from that blower to the tool, and make sure the port on each tool is also 5". If you aren't able/willing to expand the port on your tools to 5", then use a 4" hose and leave the other inlet shut.

[Rod Sheridan]

Dan's post regarding the 5 inch flex is spot on, 4" is too small for most machinery applications.

Convert your machines to 5" ports and you'll have much better results.

I use 5 inch polyurethane flex, it was about $60 for a 10 foot length and is incredibly flexible, far better than the cheap hose I was using, worth investing in.

Regards, Rod.

[Curt Harms]

This is a question directed at everyone, not just Greg. 6" hose and fittings are cheaper and easier to find than 5". Would it work to remove the side of the dust collector and make a plywood replacement with a 6" HVAC starter flange in the center? Does the H.F. D.C. have enough capacity to handle 6" hose? Would there be too much airflow overloading the motor?

[Alan Schaffter]

This is a question directed at everyone, not just Greg. 6" hose and fittings are cheaper and easier to find than 5". Would it work to remove the side of the dust collector and make a plywood replacement with a 6" HVAC starter flange in the center? Does the H.F. D.C. have enough capacity to handle 6" hose? Would there be too much airflow overloading the motor?

The answer to that is probably here or on Bill Pentz's site. But, the inlet size is often selected by a manufacturer to control the motor's current draw. If you open the inlet or attempt to run the DC with no pipe or hose, in can cause the motor to work too hard, draw too much current, overhead the motor, and pop the breaker. All that can be checked with a current meter. As long as you always connect the DC to hose or ducting, you can probably make your own inlet plate and use a 6" flange.