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2nd April 2014, 04:39 PM #31.
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The 1750 RPM is probably a mistake (Its a 4 pole motor) so it should be around 1425 Rpm OR its a 60Hz value OR he has a pulley gearing the RPM up.
Yes a fan like that will make more noise not just because the blades are naked but because they are straight, Backwards curved blades make less noise.
But the lower RPMs will definitely help and probably overcome these issues.
One issue with these paddle type fans is that stuff can tangle around the shaft more easily and they can become a PITA to untangle. OK for sanders and stuff than makes chips and dust but watch out for shavings and streamers.
Albert it would be interesting to know the noise level of the motor/impeller. Most smart phones have free Sound Pressure Level (SPL) apps available for them. OK they are not that accurate but it will give us an idea of what noise it makes.
SOP is at 1m from the unit at the same height as an operators ear (i.e. ~1.8m)
My Clearview fan is built on a disc on the side opposite the inlet presumably for strength but may assist noise reduction.
Would a Fan design that has a complete disc opposite the inlet and a annular disc on the inlet side allow the fan to rotate close to the sides of the fan housing without an increase in noise?
Ron
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2nd April 2014 04:39 PM # ADSGoogle Adsense Advertisement
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2nd April 2014, 08:14 PM #32SENIOR MEMBER
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Yes you are right Bob, it is 1450rpm drawing 8 amp
image.jpg
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2nd April 2014, 08:23 PM #33SENIOR MEMBER
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Ok I will measure it once the 3 phase installation is completed, should be around the end of next week. My power provider asked if I want to upgrade from 60amp to 100amp for 2500aud, to get 60amp 3 phase supplied to the fuse box at the boundary is 250aud. 60amp should be enough as I have star delta for the sander, it's operating current is 19.1amp.
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3rd April 2014, 12:40 AM #34
If we have the inlet completely open and the outlet completely blocked, then in some amount of revs of the fan after initial start the fan will move air into the housing until it can't anymore, the fan has reached it's limit of moving air against the rising pressure, it cannot move anymore air so we have no flow, it is at this point where I mean it doesn't matter what size the housing is, a bigger housing will just mean it might take a few more rotations to move air into the larger space before the max pressure is reached.
In an ideal machine we would have no leaks but there undoubtably will continue to be some air moved by the fan due to leaks, say the motor shaft where it penetrates the housing and any gap or misalignment between the stationary part of the housing and the inlet to the fan, both these leak points can be reduced or eliminated by design, the usual best is to have these gaps at a minimum and therefore give the best max static pressure test value.
Pete
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3rd April 2014, 10:10 AM #35.
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Pete has explained this well but I just wanted to relate the following.
Many years ago when I first started messing around with impellers I thought the same way and spent ages mucking around changing gaps and putting in baffles etc and found it made no difference to the static pressure test. What gaps etc will effect is the fan curve and the ability to deliver air under load. This is why fan curves are important
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3rd April 2014, 05:47 PM #36... and this too shall pass away ...
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Yes ... had a couple of ah-ha moments myself here as I wandered through the literature.
Static pressure only tells part of the story. Two impellers might have a similar static pressure, but one might be vastly superior at pulling air through obstructions such as machines and duct work.
Cheerio!
John
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4th April 2014, 01:59 AM #37
During the making of my cyclone I decided a flange mount would be a better option than a footmount, an added benefit was the prevention of air escaping through the motor shaft hole and as Bob pointed out in another thread some heat transfer.
Another method to slow down air escaping thru the motor shaft hole is to have the backing plate of the fan as close as possible to the fan housing, 1 or 2mm, this closeness starts to act like a labyrinth seal and thus preventing air escape.
Also in my setup the center pipe in the cyclone has a gap of about 1mm between it and the inlet shroud of the fan, pipe and fan inlet are the same size so basically it's a butt join with a gap, one part rotating the other not, this was done to separate the positive side from the negative side, an improvement might be to have the center pipe fit inside the fan shroud by 15 or 20mm so making it a bit more like a lab. seal, the aim here is to reduce these leak points to help dynamic flow as much as possible not so much for static flow, the ratio of air leaking in a static (outlet closed) to air flowing (outlet open) comparison I would think would be quite small and it would be a poor fan if it couldn't maintain these leaks in a static situation.
Pete
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4th April 2014, 11:08 PM #38Woodworker
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Been busy lately and haven't had a chance to join in. This is an excellent thread and I'm continuing to learn plenty! Bob's post number 22 provided a big "Ahah" moment for me, as he describes the relationship between bigger HP, pressure, and the physical limits of airflow through different sized ducting. I do have a DC with larger HP, but not higher pressure (only 10"), so my best use of the DC (in a one man shop) is to employ a naked duct to scrub the air. That now makes sense to me. I've been working on ducting and opening up my machines. Pics to follow in other threads. Thanks guys.Warm Regards, Luckyduck
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4th April 2014, 11:16 PM #39.
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4th April 2014, 11:31 PM #40Woodworker
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Indeed, but my problem with having friends over is we invariably drink too much beer while we check out the latest changes or acquisitions -- not conducive for much work getting done!
Warm Regards, Luckyduck
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