J. Phil Thien's Projects

Up-
I think your outside vent is a great idea.  Bill Pentz has advocated that for a long time... 

If your outside outlet is 'large', then the airflow will pass on through and you will collect very few fines in your 'drop bag'.  If the outlet is 'small', then it will restrict air flow and performance will suffer. 

Depending on your blower performance, it may not matter how much you enlarge the opening.  If your intake properly 'throttles' the amount of air the blower can gulp at a time, then you can't overload the motor.  When this protection is in place, your outlet side can only 'hurt' performance if it gets restricted. 

If the intake can take in large amounts of air, then the motor could be overloaded.  In these designs, the outlet is designed to provide enough back pressure to prevent overload and excessive current draw on the motor.   

If you are using a HF blower (or other over-the-counter, packaged blower system), they are designed to be 'under-performers' that cannot hurt themselves.  We lose a little performance - they lose a lot of potential problems.  If you start putting together systems yourself using blower packages from places like Grainger's, then you have to pay a lot more attention to those details... 

Let us know how your system turns out.  It looks like a 'clean design' that should work well for a long time! 
- Jim

Dave -
Just a few comments on your write-up... 
You made several keen observations and have deduced much of what is happening inside the separator. 

I would however be quite curious about any empirical tests you would do with your first build. 

I have worked with a few 'true' cyclone systems from small 1/2 hp to large, 10hp units.  So I understand more of what happens inside those than what is going on in Phil's Separator.  Applying some of my cyclone 'hard knocks', here is my take on things... 

Phil's device is accurately called a 'Separator'.  It functions on two levels: 1) to separate as much heavier debris from the airstream as possible; 2) To keep that debris 'idle' so it does not re-enter the airstream. 

Various 'trash can' separators have been around since the original Shop-Vac.  I made my first one in 1976.  All of them made an improvement over doing nothing.  However, they had one common trait: The best designs create the best 'whirlpool', when empty - but worked the worst when they started getting full.  The rotating air stream was being used to stir up more debris - which then made it out the exhaust. 

Phil's Baffle makes this amazing contribution - once the debris has dropped below the baffle, it is isolated from the cyclonic action above and cannot re-enter the airstream.  It also isolates that centrifugal action from the amount of debris and/or air below, so it performs quite consistently regardless of how full the can gets. 

I have these comments on your observations. 
a) I don't think there is as much 'axial rotation' as you suspect.  I can't prove or disprove it, but I suspect much of what you observed in Pitbull's video is due to the rotational airstream intersecting his round duct - I think it has to deflect and follow the circumference.  I have a square inlet on one separator and observe none of that phenomena.  Although, it does have a neutral van to divert the rotating air past the inlet. 

b) If there is substantial axial rotation, I don't know if it is a 'bad thing' to have the 'dead zones'.  Again, my experience is with tapered cyclone designs, but I suspect that a reason Phil's design works so well is that the baffle does NOT go all the way around.  As the rotating column of air gets across the open slot, there is a slight decrease in air pressure and the air flow wants to drop into the slot.  The end of that slot cuts off the downward flow and then it rotates over the slot again.  I suspect that this 'pumping' action gives the debris a pathway below the baffle. 

Remember those amusement park rides where you spin around and the floor drops out?  You don't fall down because centrifugal force is greater than your friction against the side wall.  If you had a marble and a bowling ball in there with you, they both would still fall together to the bottom at the same speed as when it was still.

c) I would not be so quick to remove the 'dead zones' and streamline the exhaust path.  I think that will also ease the ability of debris to flow out with the air.  With cyclones, I learned that if the exhaust duct was 'short' and near the top (or flush to top), we exhausted many fines that had not had a chance to be forced out of the airstream.  If we extended the duct too close to the bottom, we could start sucking out fines that had been forced out by centrifugal force, but now were to close to the exhaust.  Unlike Goldilocks, the 'just right' zone was pretty large as long as we stayed away from the top/bottom 20%. 

I don't know if anyone has built a clear acrylic or polycarbonate version of Phil's design, but they could perform the same tests we did with cyclones...  We use a variable speed motor and smoke.  By running the system much slower, you can observe much more.  As the speed is increased, you can observe where flow changes and what doesn't change. 

Again, the beauty of Phil's design is its simplicity and practical results.  It does not take much to get substantial benefits.  It also scales quite well. 

Perhaps Phil can chime in with the results of his many prototypes and his test results...

- Jim

Has anyone made any measurements or calculations for the 'extra' load of using the separator? 
There has to be a change in the static pressure between using the separator or not... 

Practically speaking, separating the chips out of the airstream increases the the overall performance of the system so the load of the separator itself is rarely noticed.  Only passing the 'fines' and not heavier chips permits the system to operate at a lower level and still work extremely well. 

However, my woodworking shop is re-organizing and we are trying to make one 10hp DC cover as many machines as possible.  In the old layout, it handled (10) 5" ports on sanders pretty well.  However, we are hoping to enlarge some ports on some different machines.  On paper, the numbers calculate VERY close to working.  If the Separators are a net gain/load it may tip the scales. 

Any measurements or calculations anyone has made would be greatly appreciated!

Thanks!
- Jim

Phil -
Thanks for the confirmation. 
An additional assumption that I have has been mentioned in other posts: The height of the container is irrelevant to the separators performance - everything above the baffle is critical; below the baffle doesn't matter.  The 'taller' the can, the longer you can wait to dump it, it just gets heavier... 

Thanks again for the reply!
- Jim

Phil -
I understand what you are saying...  My kids have 'lost' a few toys because I thought I would have more 'fun' with them... 

In trying to understand what you are saying about the cones and CFM, I think your comments mean that if you have sufficient static pressure, the separator is more than efficient enough to push so much debris to the outside that it doesn't need the help from the cone.  However, once you filter starts getting clogged, the air stream slows down enough that the center duct could pull debris into it rather than circulating to the outside to drop below the baffle. 

In a real-world situation, I assume that when the airflow slows enough for the cone to help, you probably aren't pulling enough air into your tool ports.  Before your baffle needs help, you probably have too much dust on your machines and workpieces.  Since we rarely over-design our intake and dust ports, they end up being our indicator of overall system performance. 

I am needing to improve my DC system - the shop is 'clean', there is rarely anything on the floor.  However, my air is 'dirty' - the amount of airborne fines needs to be reduced.  I cannot afford a new cartridge system, I am hoping to improve separation enough that I can use better bags on my existing equipment.  Unfortunately, the better bags won't handle ALL the debris that is generated - so we need to separate it better. 

Your separator design works very well as a 'pre-separator' attached to each machine. I have 5 gal to 30gallon separators on various machines.  Now, I am looking to add another stage to pull out even more 'fines' to leave only 'super-fines'.  Any help with creating a super-separator will be greatly appreciated! 

My assumptions are:  Larger diameter separators work well to drop large volumes of heavier chips.  Smaller diameter separators are needed to generate higher rotational speeds to force fines to the outside.  Am I going in the right direction? 

If so, then placing a 55 gallon drum next to my jointer or table saw will easily catch the large chips they make.  However, am I better off with a 5 gallon bucket attached to my drum sander to entrap its finer dust?  In other words, is the diamter of the separator more important than just the amount of debris it will hold?

Looking forward to your reply (and others)!

A great advantage of Phil's Separator is that it maintains a very uniform performance until it overflows.  (That isn't Phil's fault - it is our own procrastination and neglect!) 

Once filled, then ALL debris gets passed on to the filter/bags.  They will clog just as quickly as they used to (before using Phil's separator).  Then with the DC clogged, no air passes and the dust piles in your machines and you can't figure out why you are ankle-deep in sawdust.   

Then... you remember that you once dumped your trash can and maybe it would be a good idea to check it again... 

Phil (or others) -
Have you experimented or tested a conical baffle?
(Where the center 'point' is higher and slopes down towards the cutout area) 

I was wondering if this would improve separation by working like an inverse-cyclone... 

Just wondering! 

Adding to the discussion...  

IN REGARDS TO EXHAUST DUCTING...
Since the 'exhaust' duct is larger, there will be a decrease in air velocity.  However, since it is AFTER the Separator, the larger chips have been removed and only 'fines' will remain in the airstream.  Since these will float along more easily, a slower air flow is acceptable.  

One thing that is being overlooked with the CFM & FPM Calculations is Static Pressure.  This is perceived as the amount of 'suction' you can feel.  The amount of static pressure your blower can work against is the truest measure of its efficiency.  Many systems can move a lot of air when they are unrestricted, but as soon as filters or bags begin collecting debris, they quit in a hurry...  

This is why Phil's separator is so beneficial, it removes the vast majority of the debris from the airstream so the filter/bag can work for a much longer time before getting 'clogged'.  

Blowers require 'some' amount of static pressure.  Particularly, those on high efficiency cyclones.  Without ANY back pressure, the blower is overloaded with incoming air.  The motor is working too hard and is likely to burn out in a shortened life.  If your motor does NOT draw too much current when the exhaust ducting/filter is removed, your blower is inefficient.  Some systems were 'designed' that way - to be so inefficient, they cannot overload the motor with too much air.  Unfortunately, most of the DC systems we get from HF and others are under-performers - so they can't create problems...

In a well designed system, you would fine tune the size of the exhaust ducting so that it provides just enough back pressure that the motor runs at its 'full load' amp rating.  Then, the bag/filters are sized so they are large enough to accept a reasonable amount of 'debris' without reducing the performance of the system.  The more material that is removed 'upstream' by the separator, the longer the cycle time before you have to clean/change the filter/bags.  

However, in the 'real world', we buy the biggest DC unit we can afford and accept its performance as our realistic standard.  

REGARDING THE 'FUGITIVE' DUST:  
My assumption is that this is dust that has escaped your dust hoods on your machine and has never entered your DC system.  As opposed to having gone through your system and passed through your filters as 'fines' that are too small for your filters...  

If they are the latter, I consider it a very serious problem.  Your "Dust Collector" is now a 'Dust Circulator'!  It is taking the most dangerous fines and pumping them into your air.  

If it is the most likely cause of not getting into the system, what is the source?  Chips from a jointer are generally larger and heavier - they are a nuisance, but less of a health hazard.  If they are coming from a sander, then it requires more serious attention because of the health risk.  

Better hood designs are always being developed and everyone has their customized tricks to suit their equipment and needs.  However, nothing beats having plenty of CFM to draw those fines into the system.  Being able to improve hood designs is critical because 40mph airflow cannot compete with the chips from the teeth of a 150mph saw blade.  

On table saws, most of the better hoods I have seen and used have restricted the openings around the base that permit 'clean' air to enter the saw and get sucked into the system.  This permits 'dusty' air to float away without being drawn into to the system.  However, you can't seal everything, you have to allow at least as much area for inlet as you have in your ducting.  If you don't allow enough air into the saw, you won't have enough CFM for the higher speed velocities to carry the chips to the separator.  

For health reasons, I would get a simple box fan and place a square HEPA filter over its 'intake' side.  Tape off the sides or open space so it has to draw through the filter.  Hang it overhead and have it blow towards you at your machines.  This will provide a supply of 'clean' air for you to breathe.  It will also keep those 'floating fines'  stirred up until the get caught in your HEPA filter.  It is a poor man's way to keep breathing clean air...

Hope these ideas help you think of more ways to make your system work better!