Hydraulics & Pressure
Net Pump Discharge Pressure
NPDP
Net pump discharge pressure is the pressure the pump itself actually adds — the discharge pressure minus whatever the intake is already supplying. It separates the pump's own work from the help a pressurized hydrant is giving.
When a hydrant feeds the intake under pressure, the pump does not have to create the whole discharge pressure from scratch — it only adds the difference. Net pump discharge pressure is that difference, and it is what reflects how hard the pump is truly working.
Drafting from a static source is the opposite case: the intake brings nothing (in fact the pump must overcome lift), so the net pump discharge pressure is the full job. Thinking in net terms keeps the operator honest about the pump's real load.
Where this shows up
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