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Thread: SCMS Dust Extraction
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27th September 2014, 09:08 PM #61
Thanks as always Bob.
The reason I stipulated this as a test parameter was to see the difference between the vent to outside being open and that same vent being blocked off. So - Vent to outside open means I had it open (with louvres on of course), and vent to outside closed means I blocked it with a piece of timber duct taped over the opening.
Might start out tomorrow with some sealant and a caulking gun.
Rather than take out all the louvres (which are factory manufactured), I might remove the whole louvre assembly, which will be a 150mmx500mm opening and see what happens.
The vent is in a fairly well protected spot, between the back wall of the garage and a fence (and about 4 feet between). Very very unlikely to see any driving rain ... so I could even have a go at removing half of the louvres and see what happens. Putting them back if required is then just more pop rivets.
If nothing else, its a learning experience !!
BTW Bob - can you describe - or point to - procedures to perform simple SP tests ? I have looked at Pentz, but we talk about pitot tubes and wotnot. What tests have others done by comparison ?Glenn Visca
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28th September 2014, 12:03 AM #62.
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OK. If your enclosure, doorway and vent are truly sealed you should see the full pressure "push" capability of your DC.
You can measure the reverse of that (i.e. the "pull" capability) by simply sealing the inlet to the impeller off with a piece of metal/wood/plastic and a rubber gasket and attaching one arm of the manometer to a hole in the blanking plate.
Rather than take out all the louvres (which are factory manufactured), I might remove the whole louvre assembly, which will be a 150mmx500mm opening and see what happens.
The vent is in a fairly well protected spot, between the back wall of the garage and a fence (and about 4 feet between). Very very unlikely to see any driving rain ... so I could even have a go at removing half of the louvres and see what happens. Putting them back if required is then just more pop rivets.
If nothing else, its a learning experience !!
BTW Bob - can you describe - or point to - procedures to perform simple SP tests ? I have looked at Pentz, but we talk about pitot tubes and wotnot. What tests have others done by comparison ?
Some info in this thread https://www.woodworkforums.com/showth...08#post1548608
A simple SP test can be used to measure how effective a port design is working or how well a machine is breathing (collecting air). One arm of the manometer (lets call this P1) is attached to the ducting a couple of meters down air stream from a machine and then the ports on the machine are manipulated (e.g. position changed or enlarged or both) to minimise the pressure difference. There is an issue about the direction of P1 into the air flow and the distance of P1 from the wall but provided these are consisted then relative comparisons are OK)
Pitot tubes are used in conjunction with a manometer to measure pressure in a moving air stream and the results can be used to calculate air flow. This gets real complicated really quickly. It's probably best to stick to SP measurements for the moment.
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29th September 2014, 10:43 AM #63
Yesterday I did some work with duct tape and butyl mastic, along with doorway draft stop to improve the seal on the enclosure.
With the original Louvre in place, I got a reading of 3/4" w.c. as a comparison to the original tests, clearly indicating the enclosure seal to the shed was much better.
I then removed the Louvre in its entirety, and read 3/8" w.c.
Ignoring turbulence created by the louvres, removing the assembly effectively doubled the vent area to 2x intake and I am still not down to the desired pressure of 1/4.
If I take it to logical progression, simply adding another Louvre of the same size along with the original will return me back to 3/8.
So, I might have a look at getting a second and larger Louvre manufactured.
Is it too bold to suggest the minimum vent size needs to be more like minimum 4x intake ?Glenn Visca
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29th September 2014, 11:27 AM #64.
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Check.
I then removed the Louvre in its entirety, and read 3/8" w.c. Ignoring turbulence created by the louvres, removing the assembly effectively doubled the vent area to 2x intake and I am still not down to the desired pressure of 1/4.
If I take it to logical progression, simply adding another Louvre of the same size along with the original will return me back to 3/8.
So, I might have a look at getting a second and larger Louvre manufactured.
Is it too bold to suggest the minimum vent size needs to be more like minimum 4x intake ?
However. this is also for externally located enclosures so for internal enclosures an even lower pressure loss will reduce the amount of fine dust likely to get back into the shed.
I notice your louvres are sort of V shaped. What about seeing if you can get them designed with just a "/" shape.
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29th September 2014, 04:23 PM #65
Go figure. I removed half the louvres and reinstalled the assembly. W.c. returned to 3/4". Even though area is larger, I gained little. Turbulence must be a factor more than one realises.
Bob, no problem with your advice previously. If I have inferred bad advice, I do apologise. Most definitely NOT the case. I didn't read your advice correctly, nor consider the impact of the louvres as manufactured.
FYI .. an image of the Louvre profile.
Back to Reece HVAC, and this time a vent 150 x 1060mm (where prior was 150 x 500).Glenn Visca
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29th September 2014, 05:09 PM #66.
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Hi Glen,
Yeah that turbulence is a BIG problem in ducting systems.
At work we used to use an expensive ABS square plastic mesh with ~ 10 mm spacing to support polyester pre filters.
Eventually someone notice how much it affected the flow so we tried replacing it with a number of products.
In the end we settled on PVC garden trellis mesh that had no significant impact on the flow and was also much cheaper.
I hope I'm not causing you unnecessary expense - have you though about making your own louvres?
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29th September 2014, 07:56 PM #67GOLD MEMBER
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If it were me I would skip the louvers. Put a furnace filter or spun filter fabric over the bigger opening to catch a little more stray dust and put a sheet of plywood on standoffs 4" to 6" from the wall to hide and protect the filter. You get a little more protection and less air restriction, well at least until the filters get coated. That's what I would do unless Bob has reason not to, that I don't see now. I'll add that I would also put a sound absorbing material, drop ceiling panel maybe, on the back of the plywood to absorb some of the sound coming back into the shop.
Pete
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29th September 2014, 09:24 PM #68.
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I wouldn't suggest using any filter media as it will just add to the back pressure..
Unless the DC leaks (which nearly all do) the very fine dust coming through the filter bags won't be caught by the furnace filter material anyway and if it does as it blocks up it will further restrict the flow.
I don't think he's that worried about noise, if he was he would be better of using a baffled box / muffler arrangement.
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29th September 2014, 09:53 PM #69
Hi lads,
Bob .. no issue about costing money. If I don't want to, I won't.
I am currently chewing on how to make my own vent. I am not really set up for working on metals, with most of my equipment dedicated to woodworking.
I could look at something out of light marine ply, with some ally angle to broadly look similar to what I have already installed.
Pete .. am thinking about your suggestion too. Am not worried (should I be ?) about dust going outside as its post filtration by the DC fine filter bags.
I have done some prelim testing on noise levels. So far. It seems the ducting generates more noise than the machine itself.
I am able to add interior wall panelling and sound proofing to the enclosure if I need to, although, its lower on my to do listGlenn Visca
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29th September 2014, 09:58 PM #70
Oh ! One more thing. I went to Mitre 10 today and bought myself a cheapy tap and die set in readiness for SP tests. It came with M4, 5, 6 and 7. Tested the NETA micro irrigation fittings in store, and perfect match for M5 thread. Home we go and onto test piece of PVC with the M5 tap.
Attempt to thread micro irrigation tap .. no go. Hmmm ... 30 mins later and a little cursing ... I realise the kit had 2 x M4 and 0 x M5 in error !!Glenn Visca
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30th September 2014, 05:09 AM #71GOLD MEMBER
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Oops sorry, dumb cold climate dweller. For some reason I was thinking the air was being returned to the shop.
Pete
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30th September 2014, 12:50 PM #72
While chewing on my external vent situation, thought I would start some testing.
For Max SP, I read 7 7/8".
I then put the machine back in its enclosure, closed the door, left 1 duct open.
SPL in the shed at about 4' high from about 5' away was 72dB. When I opened the door, about 79dB.
Pic of setup.
Glenn Visca
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1st October 2014, 11:23 AM #73
Some more testing results that I believe I need assistance with.
(To recap) Test 1 - MAX Static Pressure tested directly at the inlet. 7 7/8"
IMAG0929.jpg
Test 2 - Static Pressure (?) tested at Point A = 7".
The same test pipe inserted at Point A, with the branch (visible below point A) blocked off.
Test 3 - Static Pressure (?) tested at Point B = 7"
An extension piece of approx. 1m length was inserted at point B, into which the test pipe was inserted. The branch at the "Y" below point B was capped off. The cap at point A remained in place of course.
DC Tests.jpg
The good news is, tests 2 and 3 were consistent. But - why the 7/8" loss ? or is my baseline test bogus ? Or does it mean system leaks closer to the D.C. ?Glenn Visca
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1st October 2014, 11:32 AM #74.
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1st October 2014, 11:39 AM #75
Thanks Bob with seven inchs w.c. what would you estimate cfm through 150mm duct.
Glenn Visca
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