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Pipe Runs for DC

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  • #16
    Re: Pipe Runs for DC

    Originally posted by jhill3264 View Post
    Umm. Yeah. So OK, back to the original topic.

    I'm not sure exactly what types of pipe the original poster was referring to. For plastic ABS (like schedule 40 PVC) would be very heavy and way overkill. Likewise, 4" Galvanized pipe, if you mean like in water pipe, would also be very heavy and a real pain to install with threading and all. Or maybe those aren't exactly what he meant, but on a forum hosted by a company that has it's roots in plumbing what do you expect ;-)

    The typical suggestions are thinwall S&D PVC pipe (ASTM 2729) or snaplock HVAC duct - 26#. Yes, one is plastic, the other galvanized sheet metal. Tons of arguments for and against plastic, so I'll leave that part alone for now.

    You need to really look at whether your dust collector is up to the task of adding ductwork. In today's game, 4" is a little small and you'll find that if you have more than 5-10 feet of pipe with more than 2-3 elbows, you'll have so much resistance that your airflow will be severely reduced. A system that worked OK with just some flex hose connected directly to a machine, may really disappoint you when you hook it up to permanent ductwork. I know, I tried it, and now I'm disappointed :-( Technically, it works, and at least it works well enough to transport most of the chips that get directed right into the dust ports, but it doesn't get the really fine dust that just floats around near the ports.

    So the next step is to go up to 6" pipe. The problem with 6", is if your dust collector simply can't move enough air (CFM) to keep the dust in suspension (about 4000 feet per second), you may end up with clogs. You may be able to get by with 6" pipe for the main ducts (horizontal), but have to go back to 4" for the (vertical) drops. That's still better than 4" all the way back to the collector.

    I'm planning to redo my ductwork with 6" S&D PVC pipe. If I find that my dust collector can't keep up with 6" ductwork all around, I'll probably try the hybrid system I mentioned with 4" drops while I begin preparing preparing to buy a new dust collector with more CFM.

    Thanks for re-jacking the thread. The idea was to use the S&D PVC or the galv. heating duct. My runs are only 10-12 feet anyway.

    So even though my DC has only a 4" port, using 6" ducting for the mains will be beneficial? I'm guessing it's less restrictive and doesn't affect pressure. Will opening it to 6" for 5 ft of a 10 foot total run (including drops) make any significant difference?



    • #17
      Re: Pipe Runs for DC

      Here's a muddy answer - it might. A lot depends on how much oomph is behind that 4" intake in your dust collector. A lot of manufacturers actually choke the inlet size down on purpose to keep you from burning up an under-powered motor. Generally they have it set up so that if you run the collector wide-open, no pipe or hose, the manufactured restriction simply will not allow enough air flow to burn out the motor. The problem with adding ductwork (or even long flex hoses) is that all it does add even more restriction, therefore less airflow.

      Although you need some fancy tools to actually measure true airflow (CFM), you can do a lot with just an amp meter. Basically, the motor works harder (more Amps) when its moving more air. You can try this yourself. Remove any flex hose or ductwork, turn on the unit, wait for it to come up to speed, then check the amp draw. Hopefully, it's already lower than the max rating on the blower motor. Now start adding your flex hose, ductwork, whatever, and check the amps again - it's probably lower, maybe a LOT lower.

      This cheapo method of measuring won't tell how much CFM you're actually losing, but it does give you a way to see just how much change different configurations can make. What you want to shoot for, in any configuration, is having the Amps drop as little as possible. You will quickly see how 90 degree turns and those dreaded 4" to 2.5" adapters really have an effect.

      I started off just "testing" the idea out with about 15 feet of 4" pipe. I noticed that the Amp draw only dropped about .5 Amps, so I figured it wasn't too bad. All of a sudden, I'm running pipe all over, putting the collector in the corner, a few branches, etc. By the time I was done, my shortest run was close to 20 feet, with a 4" flex hose after that, and the longest run was almost 30 feet, 6 elbows, and then flex host that choked down to a 2.5" fitting for the router table. On the shortest run, my AMP draw had dropped 1.5 Amps; on the longest run, with the 2.5 adapter, the Amp draw had dropped almost 3 Amps. :-(

      Of course, it still felt like it was "sucking" pretty good if you put your hand over it the opening. If you stuffed the end of the hose into a pile of sawdust, it picked it right up. But I just know that it's not doing everything it could.

      If your particular blower has a high SP rating, it may withstand the restriction better than mine did. But, since most dust collectors are designed to move air at low SP ratings, it will most likely be affected the same way. My goal in replacing the 4" ductwork with 6" is to reduce the amount of loss due to restriction in the pipe. The caveat will be whether my dust collector will have enough guts to keep the airspeed high enough to keep the dust in suspension.

      One word of caution. If you start modifying the blower inlet or housing to reduce restriction, don't run it more than a few seconds and DO NOT do this at all unless you have an Amp meter to measure what you're doing. You can open up your blower beyond manufacturing spec, but only if your going to be adding some restriction down the line with ductwork.

      Last edited by jhill3264; 11-06-2007, 08:17 PM.