Tank to Pump

Pump Operations

Pump Curve

The pump curve is the relationship between how much water a pump moves and how much pressure it can make at the same time — more flow means less available pressure. It explains why pressure drops when you open another line.

A boost-versus-flow chart for a fire pump: a curve descends from the high shutoff head on the left (no flow) down through a circled rated-capacity point, then runs flat to the right — past rated capacity this training model holds the boost at its rated share rather than dropping further — with a colored operating dot sitting on the curve and guide lines dropping to the pressure and flow axes.

Pump curve · interactive

WITHIN CAPACITY225 psi boost @ 750 gpmBelow rated capacity the pump still has pressure headroom — the boost sits high on the curve. There is room to open up more flow before the pressure starts to droop hard.

  • Shutoff head (no flow)250
  • Boost at rated capacity200

The boost at each flow is computed by the same linear-droop curve the simulator's pump uses — full at no flow, drooping to its rated share at rated capacity, then held flat at that rated share past it (the pump's practical limit). A pump trades pressure for flow; it cannot give you the most of both at once. These are training estimates — follow your apparatus's own pump chart and your SOPs.

Drag the flow slider and watch the operating dot ride down the pump curve: as flow climbs toward the marked rated capacity, the available boost droops. A pump can give you maximum pressure or maximum flow, but never the most of both at once.

A pump trades pressure for flow. At zero flow it sits at churn, its highest pressure; as discharges open and flow climbs, the pressure it can hold falls along the curve. The curve is fixed for a given engine speed.

Understanding the curve dissolves a common myth: the pump does not 'create pressure' on demand. Pressure appears where flow meets resistance, and asking for more flow at the same throttle simply moves you down the curve to a lower pressure.

Where this shows up

See also