SDI (Silt Density Index)
Definition
A standardized measure of the fouling potential of water, widely used to protect reverse-osmosis and membrane systems.
SDI (per ASTM D4189) quantifies how quickly fine colloidal matter plugs a 0.45 µm test membrane. RO membranes typically require feed water with SDI₁₅ below 3–5; higher values demand better pre-filtration.
High-flow pre-filters upstream of RO reduce SDI by removing suspended and colloidal solids, protecting the membranes and extending their life.
Relevance for high-flow filtration
R+F high-flow elements serve as robust RO pre-filtration to keep feed-water SDI within membrane limits.
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Related terms
A large-format filter element designed to process very high liquid flow rates through a single cartridge, reducing the number of elements, housing size, and change-out labor compared with standard cartridges.
Absolute FiltrationA filtration rating stating that a defined percentage — typically 99.9 % (beta 1000) — of particles at or above the rated micron size is removed in a single pass.
Micron RatingThe nominal particle size, in micrometers (µm), that a filter is designed to remove — stated as either an absolute or a nominal value.
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