Backflushing filters

Woodwringer

New member
I'm in the process of installing a new Clear Vue 1800 system, and I was thinking about setting up the filters so that air would normally be blown from the outside to the inside, with the filtered air discharged back into the closet where the system is located and then ducted back into my workshop. By putting the filters inside a plenum with a diverter duct system between the plenum and blower, I was thinking that I could reverse the flow through the filters, with the air being discharged directly to the outside to clean them. I would need a port from the plenum to the exterior that would normally be closed and sealed, and a port in the duct to the normal discharge from the filters that would normally be open, but could be shut and sealed while backflushing.

Has anyone else ever set up their filters like this?
 

jsbrow

New member
Woodwringer,


Congratulations on your new CV 1800. I am building the first project since completing the install. The CV 1800 works really well collecting shavings and dust from this project.

I confess that I had difficulty picturing the details of your design, but think I understand what you would like to do. You would like a no muss, no fuss clean filter cleaning system. To clean the filters, air flow would be reversed through the filters; flowing from the clean side of the filters through the filters, exiting on the dirty side of the filters, dislodging caked on dust. The dislodged dusty air would be discharged to the outdoors. In theory, this idea sounds like it would indeed dislodge dust from the filters, thus cleaning the filters, while keeping the fine dust out of the shop.

I do not have a back flush system integrated into my CV 1800. I will be blowing compressed air through the filter pleats, hopefully in the distant future. If the distant future becomes the near future, I too will probably consider a back flush system.



If you elect to install a back flush system, I would proceed with some caution (see below). But if I were to design a back flush system, I believe I would simplify your design by eliminating the plenum and use blast gates as the diverter system. I would assemble the CV 1800 according to Clearvue instructions with the following modifications.

First install a wye at the cyclone transition (outlet). One leg would run to the filter stack and the other directed outdoors. Outfit both legs of the wye with blast gates. During normal dust collecting operations, the blast gate leading to the filters would be open while the blast gate to the outdoors would be closed.

When it is time to back flush the filters, close the blast gate at the filter transition leading to the filters and open the blast gate leading outdoors. Connect the port of the Fine Dust Collection Bin that is under the filter stack to a nearby dust collection drop, with all other blast gates closed. Turn on the cyclone.

Air would be drawn from outside the filters through the filters into the interior space of the filters, flow through the Fine Dust Collection Bin (on which the filters set), flow into the cyclone via the nearby machine drop, pass through the Blower Housing Transition, and then outdoors through the open blast gate at the transition wye.

I suspect best results would be achieved by matching all fittings, hoses, and pipes to the cyclone inlet size, which is 6”. This would give maximum air flow. Also, because there is such a large filter area, I wonder whether enough air would pass through the filters to actually dislodge the dust. If this turns out to be the case, the pressure in one section of the filters could be increased by blocking air flow from other sections of the filters, by wrapping paper around these other sections of the filter.

If the nearest drop to which you could connect the Fine Dust Collection Bin is too far away, you could add a wye fitting near the cyclone inlet with both legs of the wye fitted with blast gates. One leg of the wye would connect to the duct work system. The other leg would connect to the Fine Filter Dust Collection Bin setting under the filters. In normal operation, the blast gate to the duct work near the cyclone inlet would be open, while the blast gate to the Fine Dust Collection Bin would be closed.

Words of caution:

1) It is my understanding that high performance filters are designed for one way air flow. Clearvue anticipates air flowing from a filter’s interior where pressure is relatively high, through the filter and back into the workshop. Therefore, it may be prudent to call the filter manufacturer to determine whether back flushing would damage the filters or affect the warranty.

2) In your description, it sounds as if during normal cyclone operation, dirty air from outside the filters would pass through the filters, and filtered clean air now inside the cylindrical filters, would be returned to the shop. Since, I understand that filters are designed for one direction air flow; checking with filter manufacturer before reversing normal air flow could prevent problems down the road.

3) A last concern is whether unconditioned air from the outdoors could enter the area around the Blower Housing Transition. Cold air in the winter could lead to condensation in the transition and cause problems. Therefore, I would want to take steps to ensure this did not become a problem.
 

Woodwringer

New member
Well, it turns out that this is not a good idea. I talked to Dick Wynn yesterday, and he said that the nano filters provided with the Clear Vue system are designed for the dust to go to the inside of the filters. The coating on the paper sheds dust from the inside, but not the outside. He also said that the pressure provided by reversing the flow of air provided by the cyclone blower would not be sufficient to loosen the dust. He recommended using pressurized air, not exceeding 80 psi, and held with the nozzle at least 2-3 inches away from the outside of the filters. So that's what I'll do when they eventually need cleaning. Saved me a bunch of work building an enclosure that wouldn't have worked well.
 

Squarenuts

New member
Woodwringer,

I'm hoping this is D. G. Jones from the Gallery, if it is not, please forgive me and disregard this message.

In about a week I'm going to be starting the install of my new Clear Vue, and was quite impressed by your diverter.

I am very curious about how you like it's performance. How efficiently is the air routed (i.e. does much go the other way)? Does the dowel shaft stay sealed well? Is it loud outside when you're venting that way? Is there anything you would change

I've been putting in a lot of time trying get my install design up to spec and this looks like a much more elegant solution than my own blast-gate style diverter design, and your input would be much appreciated!

Thank you kindly,
Aaron Rivers
 

Woodwringer

New member
Squarenuts,

I am David G. Jones and I am pleased to say that the diverter works very well. There is virtually no leakage around the dowel shaft, and leakage around the diverter flap is minimal. I tried to keep the clearances as low as possible. The dowel was a tight fit in the holes in the MDF panels that form the sides of the diverter assembly. The end of the diverter that touches the curved polycarbonate plastic panels was beveled on both sides to improve the seal in the contact area. Airflow coming out of the blower helps to hold the diverter in place. I have about 20 feet of flex duct between the diverter outlet and the louver panel mounted on the gable end wall of my shop in the attic. It really cuts down on the noise, and it has hardly noticeable from 50 feet away. My closest neighbor is about 200 yards away in the woods, so I don't really worry about sound. In the winter and summer I keep it in the recirculating mode so I don't lose any heat or cool air, but in the spring and fall when the weather is nice, I use the exhaust duct.
 

Squarenuts

New member
Well sir, I thank you. I'm going to be making one post haste!
I do have a few ideas to implement, I'll be making my gallery listing soon and will make sure I give you credit for inspiring at least this one small piece. Awesome shop by the way!
 
Top