I decided to upgrade my dust extractor in steps to see what made a difference either good or bad. I also decided not to destroy any component during modification si I could return the unit back to standard.
Step 1 = upgrade the inlet from 5" to 6"
Made a new front from ply and added a 6" PVC pipe. routed a radius on the intake
My main concern was that the impellor was 12" but the centre section was reduced in blade size for 5" to match the existing 5" intake. I wasn't sure whether the larger opening would reduce pumping efficiency
Attached this to the impellor housing and ran more tests.
(NB. " H2O stated are conversions from mm H2O)
Maximum static pressure - Before 6.89" H2O, now 7.28" H2O - thats good!!
Current draw with inlet open and filter pipe disconnected - Before 3.36A, now 3.98A - thats good!!
Current draw with inlet connected to main ducting but pipe to filter disconnected. Before 3.30A; now 3.5A - good
Current draw with ducting connected and filter pipe connected. Before 2.78A; now 2.67A - thats Bad!!
CFM before approx. 450 CFM; now 456 CFM - Note. I was now taking readings in a recommended vertical matrix then running through a std, deviation spreadsheet so resulting figures are more accurate. So in reality, no real change in CFM.
All the tests seemed to indicate that while the increase in inlet looked good the restricted outlet was hampering the system.
To test this, I ran CFM tests and Amps tests
1) outlet pipe disconnected from the filter - result was 3.5A and 750 CFM.
2) outlet housing removed to expose large rectangular outlet - result 3.71A and 900 CFM. Further testing seems to have this figure steadily at at approx. 860 CFM
2) All back together again as normal - result 2.79A and 456 CFM
A this was a 2nd hand unit and the pleated filter was probably 5 years old and looked crusty, I removed it and fitted a needle felt filter that had been conditioned previously.
Results 3.5A and 665 CFM - thats great!!! So one of the problems was blocked filter.
Hopefully I can raise this figure further by removing the restricted outlet by opening it up from 5" to 6"
I'm halfway there.