saw dust piling

[OneWithWood]

Here is a pic of the sawdust exhaust pipe from the barn



I park my dump truck under the outlet and attach a tarp to the pipe to help contain the sawdust.  The force of the exhaust is such that the sawdust is blown out to the sides of the dump box.  I would like to get it to just pile up into the box.

What are some suggestions for slowing the flow of the exhaust without restricting the effectiveness of the blower?

[beenthere]

Might it help to increase the size of the pipe at the elbow? or maybe just before the elbow?  Go to three times the diameter you have now.  Same volume of air/sawdust but the velocity should drop drastically. Will admit this is just a guess.

[broker farmer]

Your pipe appears to be about 6" diameter.  Cut it off about 1ft. from the building and replace it with 8-10 inch pipe.  You'll be effectively stepping up the pipe size which will give you more volume and less velocity at the end point.  The only other thing you might try is to slow down the fan speed.

[joelmar10]

Not knowing your airflow, I think I'd try the wider pipe right at or after the turn so the dust doesn't pile up in the pipe.  If the dust doesn't all get blown out on the horizontal stetch it would build up and harden over time from moisture.  Then you'd have to clean it.   :(  Even if the dust is freefalling down the pipe you'll still have a mess of it airborne from that height.   Maybe you could build a pipe "octopus" at the same pipe diameter to spread it over the entire bed.  Wouldn't look great.  Maybe use some of that self rolling pvc stuff like they use on downspouts so it doesn't look so huge hanging there.  Just thinking out loud.     

[Shawn]

You want to slow down the speed of the air/dust at the outlet. I would suggest going to a larger pipe just before or after the elbow. If you could find a small drum and and attach the horizontal pipe to it off center and that allows the air/dust to spiral down the sides and fall straight down.
Shawn...

[Tom]

Put a 90 on the end of the pipe and a tarp on the truck.  Blow the sawdust toward the front of the truck and fill the whole truck.

Limit your sawing to Southern Yellow Pine.  We Southern types dont move too fast anyway and it might be easier to handle.  Matter of fact, you might have to get another fan to help get it out of the pipe since it's probably pretty comfortable in there.  ;D

[joelmar10]

had another thought.  maybe at the end of the pipe put on another 90 degree elbow and have it blow into a solid plate of some sort attached to the end of the elbow to bust up the flow.  would that be called a diffuser plate?  cheaper than changing out the pipe. 

[ronwood]

Would a small cyclone help to slow it down where the sawdust drops down  and the high speed air comes out the other end. The following website might help to build a cyclone. http://billpentz.com/woodworking/cyclone/index.cfm

Ron

[alwaysoily]

I think Ronwood is more on the right track.  We used to have a similar set up at the cabinet shop I used to work at as a boy.  :D       (I always wanted to say that) Try replacing the elbow with a "T" and a piece about 2ft up from the "T" and connect the remaining tube down below.  Kind of a cheap cyclone, but the theory is that the air goes up and the dust goes down, you are still cutting the air pressure in half but will still have enough to push the dust up to the point of falling down the shute.  Probably stil have some of the finer dust go up, but the heaver stuff should fall down.  Might be a little cheaper too. On the safety note, make sure that your exhaust line is grounded, sawdust makes alot of static electricty and I have seen it blow up shops and create fires

[Larry]

Cyclone sounds like the best way...looks like it would be a big job to install one at the right height for a dump truck though.

[Jeff]

Greg and I saw a cyclone at the amish auction this spring that would have been perfect. :-\

[just_sawing]

There is a reason that you see burlap on the end of shoot. This allows the air to slow down and dump the dust.

[maple flats]

They used a cyclone on old farm corn grinders (hammer mills?) try looking at auctions that contain old corn grinding equip or just drive the countryside to find an old farm that might have one in their junk pile for little or nothing.

[dail_h]

   Ann old hog feeder ,or even a fuel barrel will work good anything to let the dust drop out. Reducing airspeed preasure is what you're after.Just go in the side off centered so the air will swirl ,a 5gal. bucket stuck in the top for the air to come out ,presto -------------cyclone ---no dust problem.

[BBTom]

Ok here is what I do.  I take an old plastic barrel,  with a 4" hole saw, I make 4 holes in the top close to center. you can also just make one 8" hole if you want.  I then cut a 4" hole at an angle about 6" from the top, so a piece of 4" pvc pipe will slide in at an angle. I use a torch to soften the plastic barrel enough so it fits snug.  Then I drill another 4" hole in the bottom and stick a short piece of pvc in just far enough to stay. 

The drawing looks like this


The actual working model looks like this:


Works good for me,  Make the pipe sizes according to what you need.

[joelmar10]

Most excellent ideas.... :P


Maybe some of you cyclone/barrell fellows can compare CFMs on your blowers to get an idea what size cyclone or barrell One might need?

[BBTom]

The one I am using is an old 30 gallon barrel with a 2hp blower for the mill and a 1hp blower from the edger both piped into it.  The higher the speed inside the barrel the better it seperates the dust from the air.  Centrifigal force makes the heavier dust go to the outside of the barrel while the lighter air goes to the middle. 

[OneWithWood]

I knew I could count on this group to come up with a variety of ideas for me to ponder  8)

Here is some more info:
the blower is 5hp developing 3840 or so revs
the air speed is a bunch (highly technical term, Tom, don't spend too much time researching it  ;) )
the pipe is 6" SWD
I cut a hole in a tarp for the pipe and cover the dump box with it
the tail gate has a grain door in it so I could use Tom's idea by extending the down tube another four feet and supporting the elbow - dunno.  seems too easy  ;D
the various cyclone ideas have good merit, I would need to build a support structure for it - Hmmmm, more work, more complexity, might be on to something . . .

Seriously, thank-you all for the quick and informative responses. 

[Ron Wenrich]

We use the black flexible pipe to blow from our processor blower to a tarp covered manure spreader.  The local farmer was using it for bedding.  The pipe is just the kind that they use for drainage, without the holes.   ;)  Pretty cheap stuff.

We also use a big piece of that flex pipe to go into the trailer.  That one's a 12" pipe and not all that flexible.  Seems to hold up pretty well.

You will find that those elbows will blow out before anything else.  We have been using a sweep instead of an ell.  Sawdust is pretty abrasive stuff.  But, we do a whole lot more volume than you do.

[jack]

Yes those elbows will blow out.  BUT there is a simple solution..instead of a 90degree elbow,  use a T.  with a cap on the end,  the sawdust will pack up in the end and it will absorb the abrasivness of the material.   
I saw this being used on a facility that we regrind plastic for.... the elbows would blow out regularly, then they replaced them with T's,  the problem is fixed.

Jack