The 47 mm 0.45 micron nitrocellulose filters provided by different
filter manufacturers do not result in the same SDI results.
Millipore SDI Replacement Filters
The original Silt Density Index test procedure was developed
using a Millipore 0.45 micron, 47 mm filter pad.
SDI results obtained using Millipore 0.45 micron filters
standard or reference to which other SDI results might be compared.
Pall SDI Replacement Filters
values obtained using Pall 0.45 micron filters have been found
to be roughly 40% greater than results using Millipore filters.
The use of the tighter porosity Pall filters in SDI testing will
likely amplify the effect of the presence of finer particles
sizes on SDI results.