Improving fan performance

[BobL]

One of the men's shed's I recently visited and gave a talk about Dust to, afterwards took me out the back and showed me their recently acquired, 20 year old, 10HP, 4 giant filter bag DC that had been given to them by a large cabinet makers that had upgraded to a new system. The DC looked like it would do the job for their shed until we looked at the impeller - only 12" and very poorly mated to the impeller enclosure - too much room fr back flow inside the impeller enclosure. Now I know why the cabinet makers upgraded. When we tested the Static pressure of the DC it was only 6" so I suggested they consider getting a larger impeller and left them to it.

Now I will tell you what they did. I did not recommend this and I DO NOT recommend the average DIY does. They have had some pro advice and assistance and have taken some precautions that I will also tell you about.

Just bear in mind this particular shed has half a dozen very skilled ex-metal worker members and is one of the best metal work equipped shops in any mens shed. They took the old impeller out of the enclosure and extended the blades by welding 1" extensions onto the blades.Then they had the impeller rebalanced and re-installing it found they had doubled their Static pressure. To guard against any blade extensions coming off they have enclosed the enclosure in an 8 mm thick steel plate box,

We have no idea what the overall fan curve will be like but it will be interesting to see what happens. This cannot be usually done on most DCs because either there is not enough room inside the enclosure OR the clearances will become too small and produce a lot (and I mean A LOT) of noise.

[DomAU]

That's still not a great deal of static pressure
Certainly won't be using much of that 10HP!

[BobL]

That's still not a great deal of static pressure
Certainly won't be using much of that 10HP!

I agree - but its twice as much as what they had and it will be more than enough for their shed.
The DC has a 12" intake so 12" WC through a 12" pipe moves a lot of air.

[Chris Parks]

There is a thread or at least one post somewhere in the archives of a forum contributor doing the same thing and as far as I recall he didn't die and it was successful.

[BobL]

There is a thread or at least one post somewhere in the archives of a forum contributor doing the same thing and as far as I recall he didn't die and it was successful.

Thanks Chris. There is also a story around (from before I joined WWF) of a home made impeller that suddenly started vibrating and there was a huge grinding noise and loud bang and they found the impeller in the next door neighbours yard. It went though the impeller housing, through the shed wall and fence before it stopped.

[Chris Parks]

Thanks Chris. There is also a story around (from before I joined WWF) of a home made impeller that suddenly started vibrating and there was a huge grinding noise and loud bang and they found the impeller in the next door neighbours yard. It went though the impeller housing, through the shed wall and fence before it stopped.

There are also impellers made from plywood in service with at least one failure but all in all the RPM's are fairly low order in the big scheme of things. The science and physics may not be really top notch but functional plywood impellers are in service.

[BobL]

There are also impellers made from plywood in service with at least one failure but all in all the RPM's are fairly low order in the big scheme of things. The science and physics may not be really top notch but functional plywood impellers are in service.

Plywood is amazing stuff - lots of airplane props were made of laminated wood.
Works fine but like most rotating things it depends what hits it.

[Chris Parks]

Plywood is amazing stuff - lots of airplane props were made of laminated wood.
Works fine but like most rotating things it depends what hits it.

Like something hitting a metal impeller or a cast alloy one?