We Often Hear:
"Can you find me something that will work?"
"Sure" we say, "but it's not the dust collector's fault." At
this point we can be charitable to the competition. After all, it is hardly the
manufacturer's fault that the customer picked one out of a catalog, based his
selection on price and delivery, and bought it over the phone from an order
taker who doesn't know what the important questions needing to be asked are.
A lot of things about a dust collector are the same: a bag, a
box and a fan. If the bag or bags are big enough, the box strong enough and the
fan powerful enough, it will work in most any environment, but you must also
keep in mind that there are more than 144 kinds of dust. Answering the questions
below will help us determine the correct unit for your particular needs.
Wendell Hiester and I are in our second half century of building
dust, smoke and fume collection units. We consider the first fifty years as being on the learning
curve and at this point we don't really see the curve getting any flatter.
There are three dusts which form a baseline: sawdust, cement,
and flour. Sawdust is disgustingly easy to collect, but is explosive, especially
if it is fine. Cement won't explode or burn, but can be very hard to deal with
otherwise. Flour is both difficult and explosive. So, in describing a dust,
customers will often say it is like one of the three above.
You should answer these seven questions:
Explosive? (do you know the Kst number)
Hygroscopic? (and humidity of airstream expected)
Sub-Micron? (particle size distribution)
How Abrasive? (Moh's scale)
Static Charge? (will it stick to an inverted foam cup?)
Angle of Repose? (put it in a pile on a piece of
cardboard and then tip the cardboard and see what the angle is when it starts to
Settling rate? (throw a handful off a tall ladder and see
how long it takes to float to the ground).
Now that we have the dust identified, how about the physical
requirements for the dust collector.
Again, seven questions:
Is the dust collector to be indoors or outdoors?
What is the maximum allowable height of the dust collector?
Do we furnish a fan, and if so what is the external system
How is the area electrically classified? (voltage, phase, hertz,
NEMA 4, 12, 7 or 9)
Is compressed air available and at what pressure?
How do you want the dust removed? (drum, airlock, slide valve or
How many other auxiliary items do you want us to furnish? (Leg
structure, ladder, service platform, motor starter, wiring, sound attenuator,
after-filters, ductwork, emission monitor and start-up service)
Answers are best obtained face to face. The phone will work too,
if you give the answers thoughtfully.
--Bruce A. Beckert, President
Regarding Water Pressure; How does it relate to what I am familiar with?
Regards plus or minus 17" water gauge (abbreviated W.G.), this
is a measure of pressure (about 0.6 psig). Our ordinary dust collectors are made
to withstand this pressure. 28" water gauge = 1.0 psig (your car tires are at 35
psig). So this 17" W.G. is a very small amount of pressure. On the other hand if
there were 17" of water gauge, plus or minus, in the room you are now in, you
would not be able to get the door open to go home. The door has about 2100
square inches of surface area, so unless you lift weights at the gym, it would
take more than you could muster to pull that hard on the door knob (1275 lbs).
A. Pulse jet type cartridge dust collector efficiency is a function of the following parameters:
1. Particle size
2. Particle shape, stickiness, hydroscopic or static charge properties
3. Particle specific gravity
4. Bulk density of particles
5. Dust collector inlet grain loading
6. Filter material
7. Airstream density, temperature, dew point, or properties of gas if other than air
B. Many users of pulse jet cartridge collectors cannot answer, or sometimes even guess at the parameters
above. Even if they can, we, as manufacturers, can only use prior knowledge and some rules of thumb to determine efficiency from this data. Volumes have been written and millions have been spent, but existing technology simply cannot substitute for a stack analysis. Furthermore, an efficiency taken today is only an efficiency for today, as tomorrow the parameters will, in all likelihood, change.
C. All of this aside, we do offer the following:
1. Most dust is plus one micron in size. (One notable exception - metallurgical fumes.)
2. Most of our collectors are 99.9% efficient, by weight, on all particles one micron and over.
3. If the inlet load is five grains per CFM, at 99.9% efficiency, outlet loading is .005 grain per
D. To help you with the conversion of grain load to other common units:
1. 7000 grains = 1 pound
2. 1 gram = 15,4324 grains
3. 1 grain per cubic foot = 2288. 1 micron-grams per cubic meter
4. 1 pound per 1000 cubic feet = 16,017 micrograms per cubic meter
5. Air at standard conditions weighs .075 pounds per cubic foot
6. 44 micron size = 325 mesh (one mesh is one inch x one inch)