Thread: Sherwood 3hp 2 stage

Just to add more complications, the quoted flow rates for the 2HP of 1200CFM are "in you dreams" territory - when I measured several of these about 10 years ago the best I got was half that. I would guess off the top of my head that the "real" two stage units flow rates will be similar.

It looks like both of these units use the same 12" impeller which in the case of the 2HP unit is serious restricted in performance by
- the use of a single cloth bag
- the use of 100mm inlets

In the case of the 2 stage unit age the Pleated Filter will out-perform the cloth bag
BUT
- the old design cyclone will restrict the flow back to about the same as the 2HP unit.

Both units are basically never going to do much for small shed dust collection. The 2HP unit can be improved to a more reasonable flow rate by modding the intake to utilise 150 mm ducting. Look at the sticky thread at the top of the dust forum. Short of rebuilding the cyclone, there's no major improvement possible on the 2 stage unit .

Either way, if you want effective dust control there's no escaping the requirements to
- use short runs of 6" ducting/flex,
- use short runs of flex
- opening up of dust ports and redesigning dust guards etc on machinery

Bob, how do you measure airspeed accurately at the end of a duct when the anemometer won’t fit in the duct? I measured right at the mouth and got a reading and then held it at a bit of an angle back in the port and got a much higher reading. Neither is accurate, the one slightly inside is closer but being at a bit of an angle I guess it is also an under read.
Also for a fan blower with 200mm outlets, the exhaust velocity at different parts of the port are different, how do you get an average velocity for calculation purposes?

Thank for the reply Bob. So if I want a 2 stage dusty, what am I looking at for something half decent without wasting my money?

Regards,
Peter

Originally Posted by mic-d

Bob, how do you measure airspeed accurately at the end of a duct when the anemometer won’t fit in the duct? I measured right at the mouth and got a reading and then held it at a bit of an angle back in the port and got a much higher reading. Neither is accurate, the one slightly inside is closer but being at a bit of an angle I guess it is also an under read.
Also for a fan blower with 200mm outlets, the exhaust velocity at different parts of the port are different, how do you get an average velocity for calculation purposes?

Start by reading this DRAFT: FAQ - Dust Extraction (Practical Aspects)

Reality is, it is not possible to get sort of reliable reading at the end of any duct. The air coming out of the duct is interacting turbulently with the air immediately in front of the open duct such as any readings will be variable and meaningless.

Air flow can only be measured reliably inside a duct but even then a single point measurement is very limited. To show you the extent that needs to taken have a look in this thread.
Air flow calibration measurements

Originally Posted by BobL

Start by reading this DRAFT: FAQ - Dust Extraction (Practical Aspects)

Reality is, it is not possible to get sort of reliable reading at the end of any duct. The air coming out of the duct is interacting turbulently with the air immediately in front of the open duct such as any readings will be variable and meaningless.

Air flow can only be measured reliably inside a duct but even then a single point measurement is very limited. To show you the extent that needs to taken have a look in this thread.
Air flow calibration measurements

Gee I wish I read that before I bought my anemometer