Blower help

[Dewey]

I installed a Blower System for my LT 70 Mill that was (engineered) by a blower company for my application... 
I have 6" hose going up 16' into the trusses then 7" duct going 25' to blower then 6" duct blowing downhill 45' to sawdust building.
I know this is allot of distance to move sawdust that's why I paid to have it engineered.
We have been using it for 1 1/2 years.. We have multiple clogs daily So We've quit using it for now and Shovel it daily.
Now the company says I should up size the blower and all of the duct work..
This have been an expensive mistake .
I am wondering if you guys have used someone to size a system ?
If so who.

[beenthere]

Has it ever worked for you without clogs? 
Or are the clogs something that happened after you were using with no clogs for 1-1/2 years?

[YellowHammer]

What kind and hp blower? 

[SawyerTed]

Blower rated rpm?  Actual running rpm?  

[scsmith42]

Are the clogs between the blower intake and the blower, or the blower and the discharge?  What diameter blower and hp?

[Dewey]

Has it ever worked for you without clogs?
Or are the clogs something that happened after you were using with no clogs for 1-1/2 years?

I installed it new with the new LT 70. It has always been a hassle
 some days more somedays less

[Dewey]

What kind and hp blower? 

3HP Cincinnati Fan  

[Dewey]

Are the clogs between the blower intake and the blower, or the blower and the discharge?  What diameter blower and hp?

Most Clogs are between the mill and blower... it did clog twice on the output side.
7" on inlet side and 6" on outlet side
Fan RPM 3500

[YellowHammer]

Well, the bad news is that I've had several blowers hooked to my sawmills, and for my LT70, the minimum I could use was a 5 hp Woodmaster 5 hp Big Max DB550.  I just bought the blower, none of the stuff that came with it.  It would work 95% of the time, and clog maybe one a month on real wide, real wet wood and since I used a clear flex pipe for the first few feet, I could see the clog forming and slow down long enough for the clog to clear.  However, I only had about 25 foot of suction section, with only 10 foot of lift.   

Most duct and blower companies don't realize how heavy and wet sawmill sawdust is, they will undersize everything.  Not really their fault, they just didn't know ( I guess that is their fault, they should know...).  I eventually started working with Oneida and although I got the blower from them (they have really good cyclone blowers), I would laugh at them as they passed me to three different Oneida "dust engineers" as all three people sized and designed me three different systems!  Different pipe, different hp, etc.  I finally just made my own decision, went Big and then went to Patrick at Duct Inc to design my system, (336) 768-0701 ext 112.  He did a good job, and I recommend him.  If you call him, tell him I sent you, it's been years, but I'm pretty sure he will still remember me!  I'm sure he will recommend upsizing the blower, at a minimum.     

The suction lift section, by far, is the hardest thing for a blower to do, especially with heavy wet sawdust.  Is there a way to move your blower closer to the mill?  Just installing a bigger blower may be the fastest and least painful way to get your system running, at least most of the time.         

https://woodmastertools.com/shop/accessories/drum-sander-parts-accessories/5hp-big-max-dust-collector-db550/?srsltid=AfmBOoo0xtjhH6Sja0ZWWLyuHRqznFl3Mwlasdv2eSA19t_IAiPXSVGK

[dougtrr2]

I am struck by the fact that you are going UP 16 feet into the trusses.  Is there any way that could be lowered?  I realize that is probably to protect the ducting, but it seems like if you were lower on the wall you might get better results.

I would be cautious about upsizing the duct.  Moving that sawdust would be about velocity and pressure.  Making the ducts bigger could require significantly larger blowers just to keep the same CFM.  A 7" duct has approximately a 38.5" cross section area while a 6" duct is 28.26.  If my math is correct, then that is a 36 percent increase is duct size.  

Good luck.

Doug in SW IA

[Dewey]

I am struck by the fact that you are going UP 16 feet into the trusses.  Is there any way that could be lowered?  I realize that is probably to protect the ducting, but it seems like if you were lower on the wall you might get better results.

I would be cautious about upsizing the duct.  Moving that sawdust would be about velocity and pressure.  Making the ducts bigger could require significantly larger blowers just to keep the same CFM.  A 7" duct has approximately a 38.5" cross section area while a 6" duct is 28.26.  If my math is correct, then that is a 36 percent increase is duct size. 

Good luck.

Doug in SW IA

I need to go up 16' to give clearance for the forklifts. My Location is not a flat yard . My log deck is on the uphill side of sawmill building the sawmill is in the building on the uphill side. The blower is on downhill side of building and pulls the sawdust through duct hung in trusses and is  actually  blowing sawdust down to a sawdust building. My spot is not ideal but My land that I bought is on the side of a mountain. If I knew I was going to be doing what I am today I should have bought flatter ground

[Dewey]

A thought just came to me...  Why couldn't I put another 3 hp blower at the Hose connection at the 16' elbow and run keep the original blower where it is to push sawdust the rest of the way ? I know it may cost more to run two blowers but if it worked it would be cheaper than the labor cost to shovel and move sawdust ?

[DanielW]

For the fine dust you get out of modern bands, I'd think a 3 HP blower would probably be ok for that length and rise (though it's certainly not excessive). But you have a pretty large run between mill and blower. Is there any way you can move the blower closer to the mill? A lot goes into blower design, and this an over-simplification because there are many, many factors at play. But in general they work far better for blowing than for sucking. I think you'd have better luck reducing the suction distance between mill and blower, and increasing the blowing distance down-stream of the blower.

What I might try first, however, is putting a variable-speed drive (or VFD) on the blower. You can get cheap ones from places like Amazon that work just dandy, and you can get them for both single and three-phase output. I suspect for a 3 HP blower, you could get one for less that $250. Wire it in and it would allow you to increase your blower speed up to 50% (could go more, but usually you're safest to limit it to 90 Hz). It might void any warranty on the blower motor, but Cincinnati will have just used a standard TEFC or ODP motor that you can get anywhere for pretty cheap. I certainly wouldn't have any hesitation of running one on a blower - I used quite a few on various farm and mill applications. There a oodles and oodles of is farm and mill type folks running equipment overspeed by using VFD's with no problem.

Just make sure you size the VFD right. Depending on how the VFD is spec'd, sometimes they'll list themselves as 'XX HP', but you'll often be recommended to oversize it by 30% or so. I suspect a 7.5 HP VFD is what you'd want. Also remember: Increasing speed with the VFD will increase your static pressure at the fan and the air/chip velocity. But it doesn't give you any more power. And when you increase the speed of the blower, it will require the motor to be using more of its potential power output. If you're not tripping any breakers now, you probably have some room to play, but maybe you can only increase it to 75 Hz. or so (25% increase on speed).

I wouldn't want to make any promises that it'll work. But for a couple hundred $$ it's a very easy thing to try.

[DanielW]

Further to my last reply, a few more thoughts come to mind:

i) Am I reading this right that it bumps up from 6" to 7" at the trusses up-stream of the blower? That seems quite odd, and if it does it right at the trusses, I might interpret this that it bumps up across an elbow? That would be even more odd. When it bumps from 6" to 7", the velocity will slow down about 27%. Whenever you have a size increase/velocity-drop, the transition point is an area of concern where clogs might develop. Elbow are also an area of concern where clogs might develop. So if you're bumping up size at an elbow, you've compounded the concern.

I might be tempted to convert everything before the blower to 6" (even just use 6" duct work from the hardware store to try it out) and see if that helps. It may seem like larger duct should plug less, but I think the higher speed you achieve with a 6" pipe is more important than the larger area of the 7" run.

ii) You say it blows downhill to a sawdust building. What's your sawdust building like? It's not an enclosed building, is it? Is there a cyclone with free-vent to the outside (or if it's in a building, are sufficient windows/doors open)? If it's an enclosed building and not very well vented to the outside, you'll be pressurizing it and the blower will deadhead; it'll be spinning, but moving hardly any air. I suspect your building is open, however, so this probably isn't an issue.

[Mossy Chariot]

DanielW is right on!

I assumed what your layout looks like based on your description.  I assumed you have a 6" flex hose from your mill to the rafters and all other ductwork is smooth metal.  I also assumed a minimum number of elbows.  Based on the duct sizes you have, it would take ~1060 acfm to get 4000 fpm velocity in the 7" duct.  Wet sawdust would require around that velocity to keep the dust suspended in the flowing air and not drop out and clog the duct.  To achieve that flowrate and velocity in the 7" duct, your fan (assuming it is a centrifugal blower able to develop enough static pressure) would need to generate a static pressure of around 30" WC (water column) and would require about 8 HP assuming a mechanical efficiency of 65%.

If all your duct is 6" diameter, you can achieve 4000 fpm velocity with ~775 acfm.  Your fan would need to develop just a little more than 17" of static pressure and would require 3.3 HP at a mechanical efficiency of 65%.

Your 3 HP fan (assuming it is a centrifugal blower able to develop enough static pressure and my assumed layout is close to what you actually have) should be able to pull about 750 acfm at ~3850 fpm in all 6" duct with a static pressure of 16".

So 6" duct might do the trick and for sure 6" duct and a little more fan speed should do the trick. Hope this helps.  I assumed an elevation of 650' above sea level, a dry bulb temperature of 60 °F, and a relative humidity of 75% for these calculations.

[Dewey]

Allot of good info... THANKS.. I think I will move Blower closer to sawmill and change the inlet duct work to 6". Right now the outlet is 6" will that be ok ? By moving blower that will means it will  blowing close to 60 '.
I am going to look into  a VFD as well.


It is an open building so there is no pressure issues 

[DanielW]

Sounds like a good start to me. I wouldn't change the outlet size (not without further analyses, anyway). Change the inlet to all 6", move the blower as much as you can, and see what happens.

[Old Greenhorn]

I can't help but think the weak spot in this design is that the blower is trying to lift a column of dust 16' which means when that column is full there is a lot of (relative) weight and it all collapses back down causing the clog. Getting that velocity up will certainly help, but I think that initial 16' lift is where you have to focus you efforts.

[YellowHammer]

If you are not going up in hp, (even if you are, as I mentioned I had a 5 hp and went up from there) then things to optimize are:

Get the blower as close as possible to the mill with the shortest length of pipe possible to the suction side.

Limit the amount of corrugated plastic hose to an absolute minimum, this stuff is death to a sawdust blower system in terms of turbulent flow effects of the airstream.  In an LT70 configuration, I use 12 feet of 6 inch clear, corrugated flex, which allows head to tail of head travel and the duct mounted in the approximate middle of the mill and horizontally to the head.  At that point, all other pipe runs should be smooth metal, and the transition from corrugated flex plastic to smooth metal should be a swivel to keep the stress off the flex pipe.

Get the blower as close as possible to horizontal of the sawdust chute to limit amount of vertical lift (suction head) required.  Sawmill sawdust dust has significant density, so is harder to move in an airstream than dry sawdust such as from a table saw.  So instead of fighting gravity, try to at least neutralize it.

I have used lots of the smooth metal snap seam pipe from the big box stores in some of my earlier dust collector systems.  It is cheap and good way optimize a system, inexpensively.  Don't worry, you will not suck it flat with a 3 hp sawdust blower, and won't blow it apart on the exhaust side.

You mentioned "elbow" in one of the earlier posts, if you are using them, they are also death in terms of efficiency and head losses.  Depending on pipe size, air velocity, etc, the general rule of thumb is that a single 90 degree elbow is equivalent to 10 feet of straight smooth sided pipe.

Don't forget, you are moving much more than fine sawdust from a sawmill.  Basically anything that can go through the sawblade catcher fingers and not fall out of the open aperture underneath are going into your system.  Bark chips and "strings" from sawing act like hair and sludge in a clogged sink drain, and really aggravate things and are the catalyst of many clogs.  The fact that you can saw for a time before you clog indicates you are not completly undersized, but borderline.  You might tighten the mill fingers up to limit the amount of large solids going into your pipes.

I assume you are not going through the WM duct hose, but are attaching the blower hose directly to the 6" metal outlet duct on the hinged sawmill cover?

Also, I would probably reduce the overall solids load into the mill by dumping a larger fraction on the floor, simply by deflecting the mill's sawdust hood open up a little.   

[customsawyer]

All good points so far. I will add that I think your blower is to small for what you are asking it to do. I noticed you are in Maine. I will bet that if the sawdust touches that pipe much it will start to freeze to it on the really cold days. You need a bigger blower to keep the dust moving. I run a 30hp 42" blower (in the south) and it will still get plugged if I'm sawing really wet sawdust from cypress. All of my plugs are on the intake side.

[scsmith42]

I can't imagine a 3 hp blower working with wet sawdust.

[Jeff]

We had chip blowers and sawdust blowing systems. We're talking apples to oranges as this was a circle mill with a 9/32"  kerf,  and another system for our gang saw, so lots of sawdust, but our blowers were I think minimum 50hp.  Spinning paddles and pushing air without sawdust takes a lot of power from the gitgo.

We also used cyclones to decelerate.

[ClarkNH]

What also is not being taken into account is the fact of the air temperature 
When moving wet sawdust with low air temperature the blower will cause a super cooling effect and start to freeze the sawdust The faster the blower goes the more likely to freeze and cause issues
I utilize pvc for blower pipes to minimize the pipes conducting the cold and if at all possible, do two 45-degree elbows in place of a 90

[Dewey]

What also is not being taken into account is the fact of the air temperature
When moving wet sawdust with low air temperature the blower will cause a super cooling effect and start to freeze the sawdust The faster the blower goes the more likely to freeze and cause issues
I utilize pvc for blower pipes to minimize the pipes conducting the cold and if at all possible, do two 45-degree elbows in place of a 90

Does PVC generate static does it need to be grounded ?
I wonder what the cost difference is to Steel Duct?

[Jeff]

I utilize pvc for blower pipes to minimize the pipes conducting the cold and if at all possible, do two 45-degree elbows in place of a 90

Do you run an antistatic system of some sort for the pvc?

[Jeff]

Great minds think alike eh Dewey? 

[ClarkNH]

I have not had an issue with static build up 
I do have a ground wire/rod set up for when the flex pipe section of the blower contains metal reinforcement 
That seems to be when the system creates a static build up
Most times I'm running flex pipe with plastic reinforcement