This simulator builds the net-positive-suction-head balance term by term — source pressure head, elevation, suction friction loss and vapor-pressure head — and compares the resulting NPSH available against a synthetic pump NPSH3 reference curve and a user-chosen margin target. It is an evaluation-point calculator: change temperature, source pressure, elevation, suction resistance, pump speed, evaluation flow and target margin, and see each contribution and the final comparison update live.
• A real-time 3D cutaway workbench (pressurized source reservoir, suction lift/flooded-head ruler, suction strainer and loss section, pump-inlet pressure station, reference pump and speed plate, available-head contribution columns, and a reference/selected-target comparator) with home view, focus-selected-part, show full enclosure, exploded view, auto-rotate, expand and hide-labels scene tools. • Experiment controls: water temperature (5–90 °C), source surface absolute pressure, source surface elevation above inlet datum, suction resistance coefficient, reference pump speed, evaluation flow and chosen margin-ratio target sliders, plus pause/resume, single-step and 1 s-step buttons and four playback speeds. • A Curves & measurements analysis tab with two live charts (NPSHa vs. NPSH3 vs. selected target; reserve above target), the underlying NPSHa/margin/ratio/target equations, and snapshot readouts (evaluation flow, source pressure head, elevation contribution, suction friction loss, vapor-pressure head, NPSHa, NPSH3, margin, ratio, selected target, reserve). • An Experiments tab with four guided fixtures (available-head balance, hot water, high evaluation flow, larger selected margin showing the physical NPSHa itself does not change) and a Model verification bench with a timestamped event log and copyable trial report. • A Learn & assess tab with four guided lessons, a knowledge-check quiz with reset, and a written model-scope statement linking to a Pumps & Systems reference.
Net positive suction head available is assembled from four independently adjustable contributions: NPSHa = Psurface/(ρg) + zsource − Ks·Q² − Pvapor/(ρg). Absolute source pressure and positive elevation both add available head; suction friction loss (which grows with the square of flow) and vapor-pressure head both subtract from it. The available-head contribution columns visualize each term separately so you can see, for example, that raising evaluation flow simultaneously increases the friction-loss subtraction and the pump's own NPSH3 requirement.
NPSHa is compared against a synthetic, speed-dependent NPSH3 reference curve — the pump side of the balance — using both a raw margin (NPSHa − NPSH3) and a ratio. You can additionally choose a target margin ratio to compare against; the larger-selected-margin experiment makes clear that changing this target only changes the comparison and reserve, not the physical NPSHa itself, since NPSHa depends only on installation conditions.
This is an evaluation-point calculator, not a coupled operating-point solver — it uses a temperature-dependent Antoine vapor-pressure approximation, constant water density, a fixed quadratic suction loss and a synthetic speed-dependent NPSH3 curve. Selected ratio targets are educational controls, not default design recommendations, and NPSH3 itself denotes a head-drop test criterion rather than a guarantee against cavitation.
NPSH available (NPSHa) belongs to the installation — it is calculated from source pressure, elevation, suction losses and the liquid's vapor pressure. NPSH3 (or NPSH required) belongs to the pump itself, supplied by its manufacturer's tested performance curve. The simulator keeps these visually and numerically separate.
No. A selected target ratio only changes what NPSHa is compared against and how much reserve is reported — it has no effect on the physically calculated NPSHa itself, which depends solely on the installation's pressure, elevation and loss conditions. The larger-selected-margin experiment demonstrates this directly.
Higher flow increases suction friction loss (which scales with flow squared), directly lowering NPSHa, while the pump's own NPSH3 requirement typically rises with flow at the same time. Both effects narrow the margin simultaneously, as shown in the high-evaluation-flow experiment.
No. NPSH3 corresponds to a specific 3% head-drop test criterion, and a chosen margin above it is an educational comparison target in this simulator, not a universal design rule. Real installations should follow manufacturer guidance and application-specific margin recommendations.