Regenerative Blowers - CFM vs HG

[jsooter]

What is the correlation between CFM and HG when it comes to bigger regenerative blowers? What is the more important factor. I was looking at a 20 hp regenerative blower that has a max of 5 hg at around 300 cfm. Is that good or bad. Thanks for the help.

[Brady Watson]

Those are pretty lame specs...ShopBot's regen blower does a max of 14" Hg and 330 CFM @ 16hp. They sold a roots blower that also did 14" Hg, but it moved 600 CFM of air and used 15 HP - but it was literally 'rattle your head' loud.

I have an FPZ regen blower from ShopBot laying around that is 5HP. It is rated at 8" Hg and 200 CFM.

-B

[dana_swift]

The holding force is:

F = V * Area * C(f)

V is the Vacuum level in pounds per square inch
Area is the area of the vacuum in square inches
C(f) is the coefficient of friction between the workpiece and the bleederboard (one of those things that's not easy to measure).

If you have a lot of area, you can lower V. I don't have much area on my BT-32 so I go for high V.

No matter what you are cutting conceptually there is no flow when your material is sitting intact on the bleederboard. So a pump with infinite CFM will have no air moving at all.

When you cut through the material you get CFM up to what the pump can maintain. The higher the CFM at your minimum working V the more you can cut through before things start shifting and parts get ruined. I also can pause the file and add some quick masking tape over holes to bring V back up and bring CFM down.

And then there is the value of F in the equation, on my alpha F can reach 150lbs before the drivers fault.

V is roughly half the value of "Hg. So 20"Hg is close to 10psi. Most gages show "Hg and have no reading in psi. You can find ones that are dual scale, my primary meter is electronic and shows the vacuum level in any of several units.

My other concern is 20hp. You could use your electric meter as a fan! That thing will just be spinning.. I cringe turning on my 5hp pump any more than I have to as it makes my meter spin pretty bad already.

Directly to your question as to CFM vs Hg, it comes down to area, and what you intend to cut (through).

Hope that helps.

D

[jsooter]

Great info. It definitely clears some stuff up. I guess I need to sell that blower then. Live and learn. ha ha

How is it that such a large 20 hp blower has such inferior specs to a 5 hp blower?

Thanks