Thread: dust extractor vacuum pressure generated at nominal velocity

What you are looking at are 2 points from the fan curves for each these units.
I converted these into two point fan curves but the image up loader is not working

Screen Shot 2017-07-10 at 8.22.03 AM.png

The bigger units must be running bigger fans.
The 11kW loses 0.68 m^3/hr/Pa , the 7.5 loses 1.1 and the 5.5 loses 4.75.
As expected the bigger unit is more efficient.

You need to bear in mind that all these flows assume there are multiple machines/ducts running simultaneously.
if you attach to a single 6" duct you still wont get more than ~2400 m^3/hr through that duct.

OTOH 3 x 6" ducts (with no machinery back pressure (max vac) can run to close to full capacity with the JT350.

Thanks Bob, Did you meant 8" duct with respect to the 2400m3/hr comment? 8" = 200mm, area x speed = 0.1m x 0.1m x pi x 22m/s x 60 x 60 = 2400m3/hr?

my main is 250mm so my dusty should be something that can do 3500m3/hr at 20m/s... I am inclined to buy something thats bigger so I can put a VSD on it so its running at 75-80%.

Originally Posted by Albert

Thanks Bob, Did you meant 8" duct with respect to the 2400m3/hr comment? 8" = 200mm, area x speed = 0.1m x 0.1m x pi x 22m/s x 60 x 60 = 2400m3/hr?

I agree with your calc but I was referring to 2400 m3/hr is what a naked 6" duct will draw at 10-12" of static pressure. As soon as machines are added that will drop off.

my main is 250mm so my dusty should be something that can do 3500m3/hr at 20m/s... I am inclined to buy something thats bigger so I can put a VSD on it so its running at 75-80%.

That sounds about right but it assumes your machines have no resistance - as soon as you add the machines the flow will drop off. Large mains are only worth some thing if you lan to connect to more than one machine at the same time or your machines require multiple 6" connections - I seem to remember something about a big sander with mega flow needs?

If you run a big main with only one machine and a 6" connection you might get sawdust dropping out of suspension. Have to make sure you clear the main dust by opening up a few other connections every now and then.

Yes I still have the big sander, I think the mega flow speed is a mistake, the machine has 2 x 160mm and 2 x 125mm. at 20m/s thats 4600m3/hr. I am deciding between a Nestro NE300 or Vacumobil VP300... hopefully I can get a decision done before Xmas and have the money for it.

Some stats
Nestro NE300 is
5085 m3/hr at 2400pa
total negative at ventilator is 2950pa

Hocker Vacumobil is
5100 m3/hr at 3200pa
6000 m3/hr at 2700pa
BrikStar_CS_15-09_Vacumobil.jpg

Entstauber_2.jpg

just need to check which supplier can do more or bigger bang for the buck.

I sometimes run the machine without shutting the blast gate of the branches. to give the duct a clean