Nominal Flow vs Maximum Flow: What's the Difference?

Nominal flow rate is the recommended operating flow rate for a filter under normal conditions, while maximum flow rate is the highest flow the filter can handle under specific limits. In practice, nominal flow is the more useful number when selecting a water filter because it reflects the range where the filter is expected to operate efficiently with acceptable pressure drop and cleaning frequency.

Why the Difference Matters

• Nominal flow is used for normal filter sizing
• Maximum flow may increase pressure drop and cleaning frequency
• Sizing only by maximum flow can lead to poor performance
• Continuous systems should generally be sized around nominal flow

When choosing an automatic self-cleaning screen filter, start with the required continuous flow rate and select a model whose nominal flow meets or exceeds that requirement. Maximum flow should be treated as a limit, not the preferred design condition.