Technical bulletin: NPSH margin on high-temperature retrofits

NPSH available falls as fluid temperature rises, because vapour pressure rises with it. A suction arrangement that comfortably supported an AX-220 on 60 °C water can be marginal on the same pump at 150 °C, before any change of pump is considered. A retrofit that also raises NPSH required — as every step up the PX range does — compounds the problem.

Where a request moves an existing installation to a higher temperature, NPSH available at the new operating condition is a required input, not an optional one. If the customer has not stated it, it should be asked for rather than assumed. A selection made without it rests on an unverified dimension and should be flagged as such.