# Advice for diagnosing underperforming dust collectors?



## somervillain (Oct 1, 2021)

My dust collectors are not sucking...at least as well as a 5.5hp shop vac. I own both the 2hp and 1hp Harbor Freight dust collectors. I connected all 3 to Rockler Dust Right Separator/Cyclone. The shop vac is definitely besting them all by a visible margin. I've cleaned both thoroughly and am puzzled by what I am seeing. I wanted to start with 2 questions:

What's the smartest way to objectively diagnose?
I test now by vacuuming dust, but there must be a more precise way. I also wanted to compare my readings to other people's to ensure it's not an issue with my unit.
I was thinking of buying a cheap anemometer similar to https://www.amazon.com/dp/B07NRSYNW2/ would that be a reliable objective indicator? Is one model better than the other for this scenario?

What should I inspect in the dust collector? 
I've looked for obvious blockages
I've emptied the bags and blew them with an air compressor
I've checked for leaks

So, either I have a very fundamental misunderstanding about dust collection or something is not right. 

$70 My shop vac is rated for 100 CFM
My 13 gallon 1 HP High Flow Dust Collector is rated for 660 CFM
My 70 gallon 2 HP High Flow High Capacity Dust Collector is rated for 1550 CFM
Each is hooked up to Dust Right® Dust Separator
I also tried each with a 2.5" hose and no dust separator.
I've also tried vacuuming dust with the 4" hose on the 2hp dust collector and compared to the others.
The shop vac exhibits extremely strong suction. You can definitely feel a major difference. The 2hp one does much better than the 1hp one. Even with vacuuming the floor. The 2.5" shop vac hose will grab fine dust almost an inch farther away than the 2hp dust collector with a 4" hose and cleaning attachments or even a 2.5" hose through adapter. 

When I hold my hand to the hose, it's a scary suction for the shop vac, but with the dust collectors, it's definitely moving air, just not with a scary velocity, even thought the hoses are all the same size in some of the tests.

Is this expected? I'd assume the 2hp model would be more than double the suction, since it's rated 15x higher. The 1hp is especially weak, but is rated at 6x. What am I missing?


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## epicfail48 (Mar 27, 2014)

You're comparing a high-volume, low-pressure system to a high-pressure, low-volume system in a test that values pressure more than volume. Vacuuming piles of dust off the floor is a different task than moving large amounts of air through a filter to catch any airborne particulates, which is what the dust collector is designed for


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## woodnthings (Jan 24, 2009)

Here's what I have learned after making sawdust dust for 50 years +.
A shop vac has "more suction" than a dust collector.
You must collect the dust right at it's source of origination no matter what manner of suction you use.
The dust must be suspended in the air to be efficiently collected by a dust collector.
It will do little or no good to attach the 4" hose at the base of the cabinet and wait for the dust to slide down the ramp into the port.
The best table saws made today have blade shrouds that cover the blade with a dust port built into the cover for attaching a shop vac.
To move enough air at a high enough velocity will require at least 5 HP and a 15" blower fan.
Few home shops have this type of dust collection, capacity.
I have 5 shop vacs, (on sale at Home Depot)
I connect the shop vacs to bandsaws, belt sanders, ROS sanders, and router tables. They work fine.
I have 2 Jet 1100 CFM 1 1/2 HP dust collectors I move about in the shop to the large machines like table saws, drum sanders, and planers that are in use at the time. These machines except the table saw, make such a large volume of chips and dust that a large drum collector is required OR frequent emptying of a smaller one.
I use a minimum of 4" flex hose, less than 5 ft. to each machine.
I have a jet 3 speed air filtration unit hung from the ceiling in the wood shop.
The dust "collector" is not really a sucker, it is a blower that creates suction by displacing air and forcing it through either a bag or a cannister filter.
The more resistance in the bag from accumulated dust, the less efficient the system is. Cannisters are an improvement over bags because of their increased area. Both need to be knocked out to loosen the built up dust "occasionally" depending on usage.

I still get some airborne dust that settles on table tops, but nothing excessive.

As to measuring the amount and velocity of the air, that requires an anemometer and a static pressure device:


https://www.dustlesstools.com/blog/vacuum-strength-cfm-and-water-lift/



What you will probably find, is that your system falls below the recommended volumes and velocities. So, now what? Some folks start hooking them together in series, other try parallel. This site will get you either discouraged or totally confused, but if you can get through it, you'll have a new knowledge of fluid dynamics and dust "control":


Bill's Cyclone Dust Collection Research - Home Page



This is all about ducting:





Dust Collection Research - Ducting


This site helps small shop workers understand the risks from fine dust exposure and how to effectively protect themselves and their families from airborne dust hazards. Fine dust is so extensively studied that researchers call it PM short for particle material. A Google search on PM Health Risks...



billpentz.com


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## Rebelwork (Jan 15, 2012)

Your water hose has good pressure. Now hook up a fire hydrant hose to your home water outlet. Would you still have the same pressure?


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## woodnthings (Jan 24, 2009)

Rebelwork said:


> Your water hose has good pressure. Now hook up a fire hydrant hose to your home water outlet. Would you still have the same pressure?


Your house hold water pressure is typically from 40 psi up to 65 psi. Mine gauge says 40 psi right now.
Fire hydrants are maintained at 20 psi, but can flow around 1,000 GPM. The fire engine has a huge pump that increases the pressure because the hydrant doesn't have enough.








NFPA Guidance on Fire Hydrant Testing & How To Do It


Learn when and how cities should perform hydrant flow tests—and why these measurements ensure that fire protection systems work in an emergency.




www.qrfs.com




.


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## B Coll (Nov 2, 2019)

somervillain said:


> My dust collectors are not sucking...at least as well as a 5.5hp shop vac. I own both the 2hp and 1hp Harbor Freight dust collectors. I connected all 3 to Rockler Dust Right Separator/Cyclone. The shop vac is definitely besting them all by a visible margin. I've cleaned both thoroughly and am puzzled by what I am seeing. I wanted to start with 2 questions:
> 
> What's the smartest way to objectively diagnose?
> I test now by vacuuming dust, but there must be a more precise way. I also wanted to compare my readings to other people's to ensure it's not an issue with my unit.
> ...


There is a difference between cfm and velocity. A shop vac is sucking through a 2" hose or so. A dust collector is pulling through a 4" pipe. I have a cheap 2hp dust collector with a cyclone on a steel can. I also was experiencing some problems, but was able to eliminate them. I have a main pipe which branches off to my work stations including band saw, jointer, planer, table saw, RAS, and spindle shaper. Each station drops from the ceiling. In my case I determined it was poor quality blast gates. I was able to hear a very faint hiss from them, but I guess it does not take much. I installed good quality blast gates and the difference is amazing, gobbles up everything. So, if you are utilizing blast gates, you may want to look at that, or any other leak source in your system.


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## DrRobert (Apr 27, 2015)

What kind of filters do you have? Cheap bags can become clogged.


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## Elden Cozort (Oct 30, 2018)

My research of the Rockler Dust Right Separator/Cyclone shows that it only has 2 1/4 inch ports. If this is true and you are reducing the 4 inch lines down to 2 1/4 to the separator and then back to 4 inch to the HF blower the air flow is being restricted. 
I have a HF 2 HP blower connected to a homemade cyclone and it work well for separating. I followed advice from J. Phil Thien's Projects - Index (jpthien.com) and created a top hat separator.

If you aren't reducing from 4inch to 2 1/4 inch then "never mind"


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## somervillain (Oct 1, 2021)

I apologize if this is a dumb question, but what's the difference between pressure and velocity when the tubing is the same? With water, isn't it a function of flow and diameter of nozzle? If you attach one of those multi-pattern nozzles to your garden hose, the unrestricted one has one pressure and flows about 3 feet and feels gentle and pleasant and the small nozzle has a much greater pressures and flows like 15 feet and can remove paint off the house and hurt your skin up close.

So my dust collector, when restricted to 2.5", has greater pressure than the 4" hose, but nothing compared to the shop vac, even though the diameter is the same, but the CFM is rated 15x higher. I forgot to mention, when I was testing the 1hp dust collector, I removed the bag to rule out a dirty bag as the cause of pressure loss. The pressure increased, but it was still FAR lower than the shop vac. 

Why isn't pressure a function of the diameter of the hose and CFM? What is confusing to me is why a 100 CFM vacuum going through a 2.5" hose has at least 2x MORE pressure than a 1550 CFM or 660CFM dust collector going through the exact same hose: same length, same diameter, etc. 

Why is the community and industry consensus that CFM is more desirable than pressure? Whenever I hook one up to my tools, the high pressure vacuum seems better at catching dust and keeping an area clean. I get that the 2hp HF dust collector can capture more volume before emptying the bag, but beyond that, it's confusing...and fyi, not asking rhetorically. Since dust collectors seem to be the norm and shop vacs dedicatedly hooked up to tools seem relatively rare outside Festool setups, my assumption is there is something I am misunderstanding.


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## epicfail48 (Mar 27, 2014)

somervillain said:


> Why isn't pressure a function of the diameter of the hose and CFM? What is confusing to me is why a 100 CFM vacuum going through a 2.5" hose has at least 2x MORE pressure than a 1550 CFM or 660CFM dust collector going through the exact same hose: same length, same diameter, etc.


Because the hose diameter isnt the only limiting factor, design of the impeller pulling the air is just as important. Just because a hypothetical dust collector can move 600cfm through a 4 inch hose doesnt mean it can move the same volume of air through a 2.5 inch hose at a higher pressure, because the impeller might not be able to generate enough static pressure to force the air through. As an analogy, picture a standard 20 inch box fan. They move a fair bit of air through them, but if you were to put ducting on that and reduce the output, you wouldnt build an air compressor. The fan blades and motor wouldnt physically be able to pressurize the air

As has been stated repeatedly, youre comparing apples and oranges. Dust collectors and shop vacs are optimized for opposite ends of the scale, shop vacs are high-pressure, low volume, dust collectors are high volume, low pressure. Changing the diameter of the hose doesnt change the design of the impeller, and the impeller is what determines the absolute limits of how much air can be moved and the maximum pressures it can generate

Dust collectors are the standard for dust collection because of the massive amount of air that they move through their filters. More air through the filter, the more particulates get filtered out. That said, dust collection isnt something that happens in a vacuum, that is to say dust collection isnt solely dependent on just the dust collector. Whatever tool thats being hooked up has to be designed to play to the strengths of whatever the intended dust collection mechanism is. Most consumer tools are designed to have a shopvac hooked up to them and capitalize off the higher pressure and faster air movement generated, so just reducing a dust collectors hose down to fit something like a random orbit sander wont show any improvement because thats going against what its designed for. If you hook the dust collectors hose up to a downdraft sanding table, however, the larger volume of air that the dust collector can move will show its benefits, since instead of just collecting dust in a very small area, youre pulling from a much larger area. Dust collectors are also a lot more resistant to clogging when used to collect chips instead of dust. Good luck hooking a shopvac up to a thickness planer or jointer, youll clog the hose every time you make a pass


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## JayArr (Sep 18, 2018)

A dust collector is just a blower. It's basically just a fan in a loose fitting housing. A blower will move the rated CFM as long as there are no restrictions... ie the input and output of the system are not blocked in any way.

A vacuum is built to suck, tight tolerances are used, a different impeller, seals etc.

The area of a 4" pipe is 12.56 inches but a 2" pipe is 3.14 square inches. It's not a doubling or a factor of 2, more like a factor of 4. Reducing from 4" to 2" will not make a dust collector suck four times harder it will just restrict it and it won't run at 600CFM anymore. If a blower runs 600CFM at 4" maybe it will only run 150-200CFM at 2". That may be a good experiment with a manometer.

If you put a fan in a window and turn it on and then go outside and cover half the window with a board the fan doesn't push air out the open side of the window any faster or harder.

If you block the input of a blower I believe it will reduce the CFM capability of the system. It may develop a small amount of 'suction' but it's just a rotating fan without any seals so the pressure cannot build very high.

My collector has a CFM rating of 590, I reduced it to 2" hose and it still does not suck as well as the shop vac. Either we both have the same problem or that's just how it is.


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## somervillain (Oct 1, 2021)

epicfail48 said:


> Because the hose diameter isnt the only limiting factor, design of the impeller pulling the air is just as important. Just because a hypothetical dust collector can move 600cfm through a 4 inch hose doesnt mean it can move the same volume of air through a 2.5 inch hose at a higher pressure, because the impeller might not be able to generate enough static pressure to force the air through. As an analogy, picture a standard 20 inch box fan. They move a fair bit of air through them, but if you were to put ducting on that and reduce the output, you wouldnt build an air compressor. The fan blades and motor wouldnt physically be able to pressurize the air


Thank you for the thorough explanation! I understand now. That was really helpful and I appreciate you taking the time to explain.


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## woodnthings (Jan 24, 2009)

This sites also explains the difference between blowing and sucking, and is very much worth reading!
You need at least 1,000 CFM for FINE dust collection, which is the focus of Bill Pentz' site because of the health issues it presents.
Quoting from the intro on the home page site:
_The medical research shows the higher and longer the fine dust exposure the worse the damage. This should terrify small shop woodworkers, because OSHA testing shows most small shop workers who vent their dust collection systems inside get more fine dust exposure in a few hours woodworking than large facility workers get in months of full-time work._






Dust Collection Research - Ducting


This site helps small shop workers understand the risks from fine dust exposure and how to effectively protect themselves and their families from airborne dust hazards. Fine dust is so extensively studied that researchers call it PM short for particle material. A Google search on PM Health Risks...



billpentz.com





In my own case, I care somewhat less about the specific technical aspects, the CFMs , the static pressure, the duct sizes, the number of drops than I do, as most woodworkers, "does it actually work?" BUT, that's where we get into all the technicalities ....... 
When you buy a 1100 CFM dust collector, you assume it will work because that's what the high end woodworking store was selling, only to find out the ratings are a bit of a "scam"!
There is much more involved that one would think after a bit of research and using the DC in the shop. Flex hose is a suction "killer" for instance, but every one uses at least 4 ft or more. More than that is a real detriment to performance. This is why, in my shop, I bought two of the Jet 1100's on mobile bases and locate them as close as possible to the machine in operation at the time. I wanted no overhead runs, no drops, and in the case of my 3 tablesaws joined together, only 3 blast gates on a straight wall 4" PVC pipe leading to the DC. It works as best as I can tell. My previous "over the blade" shroud running to a shop vac was a large improvement. A zero clearance insert will also focus the suction better under the table. AND little did I know, the bandsaw is a HUGE fine dust generator, so the shop vac hose gets located directly under the table by the lower blade guides. My Craftsman 14" saws have built in dust ports at that location and they do a good job. If you can locate a shop vac hose within 2" of the your sawdust producing device, that will prove very effective in collect that dust.


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## Tony B (Jul 30, 2008)

Can the smaller HF 1HP Dust Collector be hooked up to a small cyclone and about 6' of 4" PVC and still work or is that too much to ask of the smaller unit?


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## woodnthings (Jan 24, 2009)

Tony B said:


> Can the smaller HF 1HP Dust Collector be hooked up to a small cyclone and about 6' of 4" PVC and still work or is that too much to ask of the smaller unit?


For a small shop, I would get 2 Rigid shop vacs and run a dust deputy in front of the suction hose. Even a single one and stack hem vertically on a cart which you move around would save floor space. You Tube has a few ways it can be done, pretty cool.









This one shows how to make a pretty good cyclone from two or four Homer buckets:





Because there is a big difference between saw dust, super fine dust, chips and shavings, each requires a different means of extraction. JMO.
Can the smaller HF 1 HP work? I donno, but if the 2 HP ones make just enough suction, I don't think the 1 HP one would do the job. I have said many times, a shop vac right at the source will do more than a DC on a 4" flex hose 24" to 36" away. The dust has to be suspended in the air for DCs to work well, at least that's my experience. Chips are a different story and they work well in my planer and drum sanders.


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## BigJim (Sep 2, 2008)

I have the shop vac setup like in the last post woodnthings posted, except I have the cyclone separator like this: Cyclone Dust Separator Kit for 5 Gallon Buckets 
I have a small shop now, and even with turnings it will easily take care of all the dust. With that setup no dust gets to the filter in the shop vac. I would suggest cutting rings out of 1/4 plywood that will fit on the outside of the bucket halfway up to keep it from collapsing. I did mine although I have two buckets connected end to end and I am very happy with this set up.

I really do like the space saving setup in that video, I will be making that for my setup. Thanks Bill.


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## TimPa (Jan 27, 2010)

typical dust collector piping tips - 
minimize bends in the line
minimize how much corrugated hose, maximize straight (smooth) tube
run a trunk line the same size as the DC outlet, then branch off with 4" to the machine
run a bare ground wire through the line, and connect at the dust collector chassis ground


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## JayArr (Sep 18, 2018)

> run a bare ground wire through the line, and connect at the dust collector chassis ground


Excellent idea, thanks Tim!


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## woodnthings (Jan 24, 2009)

TimPa said:


> typical dust collector piping tips -
> minimize bends in the line
> minimize how much corrugated hose, maximize straight (smooth) tube
> run a trunk line the same size as the DC outlet, then branch off with 4" to the machine
> *run a bare ground wire through the line, and connect at the dust collector chassis ground*





JayArr said:


> Excellent idea, thanks Tim!


That's just not necessary, Jay.
Our resident electrical engineer/scientist Rick Christopherson advises that home shop dust static induced explosion potential is virtually nil. If you want to avoid static shock, that's a different issue. Rick's site is here and scroll down on the left side to find "Principles of Static Electricity":


http://www.waterfront-woods.com/


See the section at the bottom, "Reality Checks" for reasons why a home shop dust explosions are not "impossible", but rare.

I was getting horrible static shocks from my Jet 1100 dust collector. I put up with it for years. Then as I learned more about static shock I realized that the large, clear wire wound input hose 7", from the the blower to the separator was NOT an electric conductor! I simply ran a bare copper no.12 GA wire from the blower chassis to the dust separator and that stopped all the static shocks on my system.


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## epicfail48 (Mar 27, 2014)

Just because something isnt likely to happen doesnt mean it should just be ignored, especially not when the method to take it from "not likely to happen" to "wont happen" is $2 worth of copper wire. A dust explosion would be rare, but unless you plan on paying to rebuild someones shop if it goes up in smoke, then you probably shouldnt advise against basic safety measures

Also, everybody aways likes crowing about how a static-induced dust explosion is rare, but everybody also ignores the fact that that isnt the only bad thing sparks can do. People tend to do other things in their shop that make having a possible ignition source a bad thing, like spraying finishes. Static shocks are also painful, and can kill electronics

Ground the tubing, the worst case scenario is you spend a few bucks you didnt need to. Compare that to the worst case scenario for not grounding it


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## woodnthings (Jan 24, 2009)

Is static dust explosion a myth? This video explains the difference between static shock and static dust explosionand the amount of dust and the size of the spark needed for an explosion:





Dr. Coles scientific analysis is linked here. Scroll down to the section labeled MYTHS:




__





Grounding PVC and Other Dust Collection Myths






www.woodcentral.com


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## TimPa (Jan 27, 2010)

woodnthings said:


> That's just not necessary, Jay.
> Our resident electrical engineer/scientist Rick Christopherson advises that home shop dust static induced explosion potential is virtually nil. If you want to avoid static shock, that's a different issue. Rick's site is here and scroll down on the left side to find "Principles of Static Electricity":


we will agree to disagree here Bill...
static is definitely generated when air moves though piping components, esp pvc pipe. and static causes havoc to electronic components (ask any CNC owner/operator), where erratic operation occurs when ungrounded DC systems are operating. 
with the ever increasing amount of electronics showing up on our woodworking equipment, not to mention any computer equipment on hand, my feelings are that i want to protect it as well. local climate plays a role in the amount of ststic which is generated. do what you wish!


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## woodnthings (Jan 24, 2009)

TimPa said:


> we will agree to disagree here Bill...
> *static is definitely generated when air moves though piping components, esp pvc pipe. and static causes havoc to electronic components (ask any CNC owner/operator), where erratic operation occurs when ungrounded DC systems are operating. *
> with the ever increasing amount of electronics showing up on our woodworking equipment, not to mention any computer equipment on hand, my feelings are that i want to protect it as well. local climate plays a role in the amount of static which is generated. do what you wish!


Actually, we do agree!
The static shock issue is different than the static dust "explosion" issue. I solved my shock issue with a bare copper wire electrically connecting the blower/motor chassis to the separator. I was getting incredibly painful shocks because the two were not electrically bonded in any way. The clear wire wound suction hose was not an electrical connection and the separator was not electrically bonded because it sat on top of a cardboard drum. After connecting the wire, that problem went away.

My point in linking those other articles and the video was to attempt to dispel the "myth" regarding home shop dust explosions.

Of course folks can do what they feel is necessary on their home shop systems, wires inside, wires wrapped partially or completely around, no wires, plastic blast gates, metal blast gates, PVC pipe, metal pipe....etc. My conclusion based on the well written and documented articles, was that the dust explosion hazard was virtually non-existent. The amount of dust and the volume of air must be considerable and in just the correct percentages and then a spark of sufficient amplitude must occur to ignite an explosion, typically in a commercial or industrial setting.

If static shock is a concern and rightfully so, then ground everything in the shop, including the cat. Little copper booties should do the trick!


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## woodnthings (Jan 24, 2009)

Here's a *great video *explaining the differences between a shop vac and a dust collector, including a cyclone addition.
He also discusses the Bill Pentz approach at $7,000 and 5 HP motors with 15" diameter blowers, that get 99.9% of "fine dust" and whether all that's even necessary for protecting your health. He concludes that a good dust mask, linked here, is a far cheaper approach:








Amazon.com: RZ Mask M2 Face Masks for Woodworking, Home Improvement, Construction and DIY Projects : Tools & Home Improvement


Buy RZ Mask M2 Face Masks for Woodworking, Home Improvement, Construction and DIY Projects: Safety Masks - Amazon.com ✓ FREE DELIVERY possible on eligible purchases



www.amazon.com










I keep finding good videos on dust collect, filtration and the Harbor Freight DC:













I have replaced the bag filters with cannister filters on my Jet 1100, 1.5 HP dust collectors. I also replaced the plastic collection bags with 30 gallon cardboard drums. I needed to make my own adaptor, show above, to the cardboard drums. I keep extra empty drums near by to quickly insert it to avoid a work stoppage during a long run of planing. Here's a thread showing some of my ideas:








Dust Collection in woodnthings shop part 1


This thread will show how I collect the dust from the table saw, jointer planer and a sliding miter saw. I use a combination of PVC couplers and dust collector flare fittings for quick change connections. I run 4" flex hose right from the Jet 1100 remote controlled DC to the flex hoses either...




www.woodworkingtalk.com


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## Rebelwork (Jan 15, 2012)

I don't get any static on my Jet. I use to get the crap knocked out of me on a shop vac. I got rid of that...


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## panofish (Sep 24, 2009)

fyi: If you don't mind the extra wait... you can usually get things like that anemometer direct from China for cheaper through aliexpress. 

Looks like you can get it for 14.24...









22.96US $ 50% OFF|Digital Anemometer Handheld Wind Speed Meter Bt-100 For Measuring Wind Speed, Temperature And Wind Chill With Backlight Lcd - Speed Measuring Instruments - AliExpress


Smarter Shopping, Better Living! Aliexpress.com




www.aliexpress.com


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## Rob Cook (Jan 27, 2021)

I have the Harbor Freight dust collector. I found that after filling and replacing the bag that I had reduced suction. After checking all the connections, I removed the upper cloth bag and after shaking it out - dust storm in the neighborhood - suction was back up. It appears that the really fine dust plugs up the cloth reducing air flow.


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## woodnthings (Jan 24, 2009)

You do understand the reason for cartridge filters is their increased area to allow more airflow. The bags do clog up readily and the first modification typically made is the addition of a Wynn canister filter. Check out You Tube for mods to the Harbor Freight dust collector, there are probably about 50 videos:


https://www.youtube.com/results?search_query=harbor+freight+dust+collector+modifications+


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## sanchez (Feb 18, 2010)

If you add the Wynn cartridge filter and a super dust deputy, your HF will be a great machine.


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## Rebelwork (Jan 15, 2012)

Rob Cook said:


> I have the Harbor Freight dust collector. I found that after filling and replacing the bag that I had reduced suction. After checking all the connections, I removed the upper cloth bag and after shaking it out - dust storm in the neighborhood - suction was back up. It appears that the really fine dust plugs up the cloth reducing air flow.



I normally tap the tye upper bag a few times before removing the clear pastic bag. I never expected day one performance almost 20 years later but works well...


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