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  • Exhausting dust collector outside

    I have a 1.5 HP dust collector, which has a 5" inlet for collecting dust. I want to vent it outside (after adding a cyclone separator) and need to make a plywood circle to cover up the large diameter hole that the filter bag fits into (20" or so). After I create the wooden circle, I need to install a takeoff in it to exhaust the machine outdoors.

    What size takeoff should I use? The same as the inlet? I was thinking of using a 6" takeoff and 6" round ductwork, and then transition to a 3.25 x 10 wall plate to terminate to the outside. Is this reasonable? The wall plate has a greater area than the 5" inlet, but a different shape.

    Here is what the machine looks like. The filter bag will be removed, the plywood circle put in its place, and then vented outside.

    I have no gas appliances in the shop, so no back drafting worries - I'll install make up air and eat the loss of heated air.
    Last edited by franklin pug; 09-04-2017, 07:50 PM.

  • #2
    Here is a pic of the vent I was considering

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    • #3
      Don't know about air but if it was water you'd bump up a size. You need to take into account how far your going, how many ellbows etc. but yea simply put bump it up a size and you should be ok.

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      • #4
        youll end up just blowing the dust outside. Your best option is to build a room for the collector and leave the bag on the system. Vent the room to the outside. If you want to make the system more efficient, find a 55 gallon drum, and cut a ring off about the size of the existing bag ring on that collector. Di-assemble that unit, and plumb the two rings inline and mount them to the wall along with the motor/impeller. Put the cloth bags on-top and attach Heavy duty plastic bags on the bottom with HD band clamps inside garbage cans with casters. When the bags fill, tap the upper bags with a stick to loosen the dust collected on them. Then loosen the clamps, drop the bags in the containers and out they go easily.

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        • #5
          Originally posted by Alphacowboy View Post
          youll end up just blowing the dust outside. Your best option is to build a room for the collector and leave the bag on the system. Vent the room to the outside. If you want to make the system more efficient, find a 55 gallon drum, and cut a ring off about the size of the existing bag ring on that collector. Di-assemble that unit, and plumb the two rings inline and mount them to the wall along with the motor/impeller. Put the cloth bags on-top and attach Heavy duty plastic bags on the bottom with HD band clamps inside garbage cans with casters. When the bags fill, tap the upper bags with a stick to loosen the dust collected on them. Then loosen the clamps, drop the bags in the containers and out they go easily.
          The only dust getting outside should be the finest stuff, as the cyclone will separate 99% of the dust (including 100% off the big stuff). Only "the fines" (invisible stuff) will escape outdoors. Cyclones are commonly used to do this, but often the exhaust air is recirculated into the shop through a HEPA filter. I would prefer to avoid the filter, and send the air outside.

          kind of like this, but instead of a canister filter the exhaust goes outdoors. I just do no know which size exhaust to use.

          Last edited by franklin pug; 09-06-2017, 01:02 PM.

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          • #6

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            • Mightyservant
              Mightyservant commented
              Editing a comment
              The fine dust is the more problematic health wise over time, it starts to get all over surrounding exterior areas which may include neighbors that might find it objectionable
              Last edited by Mightyservant; 09-06-2017, 08:36 PM.

            • franklin pug
              franklin pug commented
              Editing a comment
              Yes, the fine dust is the worst for one's health! The idea of sending it outside is for the wind to carry it away. There should be no concern for neighbor, as it will be long dissipated before it reaches anyone. the problem of keeping it inside the shop is that it accumulates, and walking around stirs it back up again.

            • Mightyservant
              Mightyservant commented
              Editing a comment
              One thing that may be of interest to you, if your shops lends itself to it, is a negative air environment. It's sounds complicated but it's not. They can be simply constructed using box fans for under $100 or into the thousands for serous work.
              By using this method the air is cleaned using a filter of your choice,( I use a 20" HEPA and a washable pre filter to extend the life of the filter) before you send the air outside.
              This greatly improves your work environment, reduces immensely the amount of dust and makes for a pleasant work space.

          • #7
            the larger the exhaust the more dust will stay in the cyclone,, you want a "high pressure", to move the dust and chips, to the cyclone, then what the cyclone is/does to use centrifugal force and low pressure to separate the product, so the larger the exhaust the more separation will occur, as there is not enough airflow to move the dust and chips out with the air,
            Push sticks/blocks Save Fingers
            ~~~~~~~~~~~~~~~~~~~
            "The true measure of a man is how he treats someone who can do him absolutely no good."
            attributed to Samuel Johnson
            ~~~~~~~~~~~~~~~~~~~
            PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

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            • franklin pug
              franklin pug commented
              Editing a comment
              So the bigger the exhaust, the better?

              If I keep the exhaust port slightly larger than the intake port, will I sacrifice CFM, or will I just exhaust more fine dust that way?

          • #8
            the cfm will be the same, that is the volume that is being moved, and it will move the same volume but the speed or velocity of the air being moved will be different, the same effect of putting a reducer on the shop vacuum it can more more stuff as the air is moving faster through the smaller orifice, and some times the larger hose will plug do to debris not being being moved fast enough because of the reduced air movement,


            so you want a pipe that will give you the velocity to move the debris through the system to the cyclone, and then the larger coming out to reduce the air flow so it can not easily carry the debris on out of the cyclone (in the cyclone the centrifugal force and gravity and reduced air velocity, to separate the air and the debris),


            I guess for an example take a piece of PVC pipe and put some saw dust in it loose, and then take a air compressor and put a blow gun on the hose and blow air into the pipe, it will blow the dust out of the pipe, but as the dust leaves the pipe it will fall to the earth, or floor, as the velocity of the air is reduced, the same CFM of air is being blow out the back of the pipe but it will not carry the dust with it as the velocity is less,

            Push sticks/blocks Save Fingers
            ~~~~~~~~~~~~~~~~~~~
            "The true measure of a man is how he treats someone who can do him absolutely no good."
            attributed to Samuel Johnson
            ~~~~~~~~~~~~~~~~~~~
            PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

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            • #9
              So if I go with a 6" round exhaust for a 5" in, do you think I'd be okay? I really don't want to punch a larger hole than that in my house. I would prefer to use the rectangle vent, as I only need to remove one brick for the 3.25x10 vent. But, if I'm going to all this effort, I should do it right.

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              • #10
                How far are you going? How many ellbows?How many tees? What material are you using? These are questions that are good to know so we can give a useful suggestion. Straight shot? Under 10'-0" ....do it.

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                • #11
                  6" will work IMO I would think larger would be some better, as said before,

                  but one time I considered much the same without the cyclone and just exhaust it outside into a small boxed in trailer, to catch the majority of the chips and dust, that was when I was planning a lot of rough lumber,

                  figured the box would do the same thing as the cyclone, and at the time I was getting the equivalent of pickup load of chips at a time,

                  Push sticks/blocks Save Fingers
                  ~~~~~~~~~~~~~~~~~~~
                  "The true measure of a man is how he treats someone who can do him absolutely no good."
                  attributed to Samuel Johnson
                  ~~~~~~~~~~~~~~~~~~~
                  PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

                  Comment


                  • #12
                    Originally posted by Mightyservant View Post
                    How far are you going? How many ellbows?How many tees? What material are you using? These are questions that are good to know so we can give a useful suggestion. Straight shot? Under 10'-0" ....do it.
                    Very short run, about 2 feet (from the collector out). Would require one 90 degree turn, no tees. Material for the exhaust would be standard HVAC supply duct (round).

                    The inlet side is a 6 foot length of 5" diameter flexhose.

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                  • #13
                    Pipe, Tubing, Duct have a roughness coefficient, the smoother the wall the less friction. The corresponding fittings are given and equivalent so say a galvanized 1 1/4" ellbow is "equal" to 10'-0" of pipe. This is done to make the design calculations easier to compute and therefore reviewable for acceptance. Tee's meters, valves different styles, internal coatings, insulation all weigh into the calculation.
                    if you can use a 45 instead of a 90 that would be have the half "equivalent length" of an ellbow and would slightly improve your flow. If you can use PVC (for example only) rather than say spiral that would very slightly improve your flow. Bear in mind these are very slight improvements however for future changes try to keep this in mind wether it's water, oil, gas, air, it's more or less the same idea. Start with the largest, smoothest material and fewest changes of direction as is practical and that you can afford.
                    Last edited by Mightyservant; 09-13-2017, 10:23 AM.

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