used centrifugal blower - looking for one in Australia

[bruce]

Nice find!!

Almost makes me want to move down-under!

[msj442]

so im assuming that this design NEEDS a steel constructed enclosure? do the panels need to be steel also. just curious.

max

[Tony]

Greg,
Reversing the motor does mot change the flow direction, it just runs very inefficiently. When you connect it up for the first time, make absolutely sure it turns in the right direvction. If it runs backwards just swap any two of the three power wires around.

MSJ,
My own enclosure with a similar (but smaller) blower, uses MDF.
The enclosure just needs to be an airtight box, strong enough to resist the total air pressure.

[msj442]

ok i guess i didnt think the panels that are somewhat large in size would hold up to the depression that is mentioned with this style blower.

[tweaks]

Has anyone on here used a Vortex blower? .As I have been looking for a centrifugal blower myself and have come across several Vortex types...One available at moment ( vortex )which is

VB - 055A - 000 and specs on tag are

2850 @ 50Hz... 318 cfm ... Pres 87Hg ... Vac 77 Hg ...

Any thoughts

Cheers

Lynds

[Tony]

[tweaks]

Sorry I should have called it a rotary vacuum / blower...as attached image

Cheers

Lynds

[Tony]

Lynds, that is a pretty big blower around 4.3 air horsepower.

I am assuming it is three phase.

Ring compressors, (otherwise known as regenerative compressors) have characteristics fairly similar to piston, roots, vane, and other positive displacement compressors. although they have no rubbing or sliding parts like most real positive displacement compressors.
That means you will be limited to very roughly 318 CFM, no matter what, but it will operate happily over a very wide pressure range.

You will not be able to control flow by throttling it, but will need a VFD to adjust the speed, or bypass air around the blower to reduce flow.

I don't know anyone that has used this type of blower in a flow bench, but it should certainly be possible to do.

The only real disadvantage that I can see is noise. Regenerative blowers scream like a siren, which is why there is a dual muffler (intake and discharge) built into it below the motor. It will still be fairly noisy though.

It may need to be built into a sound proof box, but otherwise it should work fine, once you have either a VFD or an air bypass system to control the flow.

[jfholm]

Here in the US of A on ebay there is a used cent. blower listed. They want $1200 for it. It is huge, 3000 cfm and 40" static pressure. It says it has a 40 hp motor on it. If is either 230/460 acv. Now if a person had enough electrical power for the same price as 12 vacuum motors you could really have a bench.



John

[Tony]

Once you start looking inside a few of those big blowers, it may suddenly occur to you that there is not a lot inside there, and they are all fairly crudely constructed.

With a bit of motivation and some steel, a guy could fabricate something like that fairly easily. And it would work just as well as a commercial one.

Even better, some of the commercial pressure blowers publish performance curves, and have engineering drawings with dimensions and Hp ratings !

Buying an old one sure saves a lot of work, but..........

[jfholm]

Tony,
I always appreciate your input. You always have good guidance for us on this forum. Building your own is appealing to me. I found this article on Wikipedia that gives some insight to what direction the blades on the impeller should face and why.



Was it you Tony that told us basically how to calculate how much air a fan would flow by diameter?

John

[Tony]

John,

These things are not that difficult to build. If you know the rotor diameter and rpm, that pretty much fixes the developed pressure.

All the high pressure blowers I have seen use straight radial blades, and not that many. Typically six straight blades.

The outer casing only needs to collect and slow the air coming off the rotor. It does not need to be snail shaped. A simple crude round collection drum works just as well, and is a lot easier to build.

Flow is determined by the total flow path areas through the entry eye, rotor, and outlet. With sufficient flow areas, you will not lose pressure because of pressure drops at various restriction points within the blower.

It is really that easy.
I built an experimental blower into a cut down 55 gallon drum. It worked exactly the same as a sexy commercial pressed steel volute housing. It looked a bit ugly though, and was only a rough experimental prototype, but it worked perfectly.

With the exact same rotor and motor fitted, flow and pressures were so close to being identical with either the volute or ugly drum, the difference could be ignored.

Something like that could shift a LOT of air, and cost almost nothing to put together. The VFD is the expensive part.

[jfholm]

That makes sense and the light bulb just came on. I was thinking a lot of blades would be better, but actually less would be better. If you have too many blades they actually tend to block the air path.

In example, with a wind generator they found that the three blade ones are actually more powerful than ones with a lot of blades. The ones with a lot of blades block the wind from going through so you actually get less work with a multiblade generator.

So I guess that would mean that you would get more air flow with a 6 or even 4 blade centrifugal blade air mover. Am I thinking correctly?

John

[Tony]

Yes, a Tesla turbine has no radial blades at all.

If you think about it, once the air is trapped within the walls of a sealed rotor that has at least some blades, it cannot "slip" or turn at a lower speed than the rotor. Six or eight blades would be a good choice depending on rotor diameter.

It is the blades that hold the rotor halves together, so it is more of a structural thing than aerodynamic. Greg's rotor appears to have sixteen blades which is unusual. But then it is a fairly large diameter rotor.

This one has ten blades is eighteen inches in diameter, and half an inch wide at the outer edge. The front cover is pop riveted on. As I sad earlier these blowers are usually of surprisingly crude construction.

[bruce]

There is a thread here on a large homebuilt blower I was working on but have yet to finish. I'll be laid-off from my part-time job in the next month or two and will have a few months over the Winter to be in the shop full-time so I'll put it on my list of things I need to get done!

If things keep going well in the shop maybe I won't have to go back in the Spring

Since my PTS bench is so easy to build/use I kinda pushed the large blower project aside. I also have a 3hp regenerative blower that I had tried in the past sitting here (like the gray one posted above) that is taking up space. Didn't work as we figured it would.



Edited By bruce on 1254569781