1. Hydraulic fundamentals
Flow rate
| PT | EN | ES |
|---|---|---|
| Vazão (Q) | Flow rate (Q) | Caudal (Q) |
Volume of fluid moved per unit time. Industrial-pump units in PT and ES contracts are typically m³/h; US specs use gpm (gallons per minute). Conversion: 1 m³/h = 4,403 gpm.
Gotcha: “fluxo” in PT-BR informal usage sometimes substitutes for “vazão” — incorrect. “Fluxo” is the qualitative concept of flow direction; “vazão” is the quantitative rate.
In ES, “flujo” is the standard term in some technical contexts but “caudal” is more precise for flow rate. ASME and API translations to ES typically use “caudal”.
Total head
| PT | EN | ES |
|---|---|---|
| Altura manométrica total (H) | Total head (H) | Altura manométrica total (H) |
Energy added to the fluid by the pump, expressed as height of fluid column. For water at standard conditions, 10 m head ≈ 1 bar pressure. ABNT NBR 12515 prefers the term “altura manométrica”; “head” is widely understood in PT industrial practice but is technically a loanword.
Gotcha: in Brazilian field practice, “cabeça” sometimes substitutes for “altura manométrica”. In a formal contract, use “altura manométrica total” and define the unit (m of fluid column).
Static head
| PT | EN | ES |
|---|---|---|
| Altura manométrica estática | Static head | Altura manométrica estática |
The geometric difference in elevation between fluid surface at suction and discharge, plus any pressure differential between source and destination tanks. Independent of flow rate.
Gotcha: in some PT field manuals, “altura geométrica” appears as a synonym. ABNT prefers “altura estática” because it includes the pressure-differential contribution, not just geometric.
Friction head / dynamic head
| PT | EN | ES |
|---|---|---|
| Perda de carga / altura dinâmica | Friction head / dynamic head | Pérdida de carga / altura dinámica |
Head loss due to fluid friction in piping, fittings, valves, and process equipment. Scales approximately with Q² for turbulent flow.
Gotcha: PT “perda de carga” maps to ES “pérdida de carga” cleanly, but in EN “head loss” and “friction head” mean the same thing in most contexts. Some EN texts reserve “head loss” for total dynamic losses (friction + minor losses + acceleration head).
Operating point
| PT | EN | ES |
|---|---|---|
| Ponto de operação | Operating point | Punto de operación |
The intersection of the pump curve (H vs Q) and the system curve. Where the pump actually runs.
Gotcha: in Spanish documents, “punto de funcionamiento” appears as a synonym. Both are correct; “punto de operación” is closer to the international convention.
Best efficiency point (BEP)
| PT | EN | ES |
|---|---|---|
| Ponto de melhor eficiência (PBE) | Best efficiency point (BEP) | Punto de máxima eficiencia (BEP) |
The flow rate at which the pump achieves its highest hydraulic efficiency. On a centrifugal curve plot, BEP is where the η curve peaks.
Gotcha: the abbreviation “BEP” is universal in international practice; PT engineers often write “PBE” as the formal abbreviation but verbal usage is mostly “BEP” because it appears on imported curves and datasheets.
The allowable operating region per ANSI/HI 9.6.3 is 70%-110% of BEP flow for centrifugal pumps. Outside that band: recirculation (below) or cavitation onset and motor overload (above).
Net Positive Suction Head — Available (NPSHa)
| PT | EN | ES |
|---|---|---|
| NPSH disponível / NPSHa | Net Positive Suction Head Available / NPSHa | NPSH disponible / NPSHa |
The absolute pressure available at the pump suction flange, expressed as height of fluid column above vapor pressure.
NPSHa = (P_atm - P_vapor) / (ρ × g) - H_suction_static - H_suction_friction
Calculated by the buyer/system designer from system geometry, fluid properties, and operating temperature. Decreases as fluid temperature rises (vapor pressure increases) or as suction pipe friction grows.
Gotcha: “NPSH-d” appears in some Spanish documents as an abbreviation for “disponible”. The international convention is “NPSHa”. Use NPSHa in contracts to avoid ambiguity.
Net Positive Suction Head — Required (NPSHr)
| PT | EN | ES |
|---|---|---|
| NPSH requerida / NPSHr | Net Positive Suction Head Required / NPSHr | NPSH requerida / NPSHr |
The minimum NPSHa the pump needs to operate without cavitation, measured per ANSI/HI 14.6 by the 3% drop method — progressively reducing suction pressure until pump head drops 3%.
NPSHr is published by the manufacturer and varies with flow rate; it is not a single number but a curve.
Gotcha: “NPSHr” measured by 3% head drop is not the cavitation inception point. Cavitation begins before 3% drop. ANSI/HI 9.6.1 recommends a margin (NPSHa - NPSHr) of at least 0.6 m, with 1.0 m preferred for industrial duty.
Cavitation
| PT | EN | ES |
|---|---|---|
| Cavitação | Cavitation | Cavitación |
Formation of vapor bubbles in low-pressure regions of the impeller, followed by violent collapse when pressure recovers. Damages metal, generates noise, and degrades performance permanently.
Symptoms: irregular noise (often described as “gravel passing through the pump”), vibration spikes, head and efficiency drop, rapid impeller wear.
Gotcha: in Spanish-to-English translation, “cavitación” sometimes appears mistranslated as “caving in” or “collapse” — these are mechanical-failure terms, not hydraulic-phenomenon terms.
Affinity laws
| PT | EN | ES |
|---|---|---|
| Leis de afinidade | Affinity laws | Leyes de afinidad |
Scaling relationships for centrifugal pumps under speed or impeller- diameter changes (with the other held constant):
Speed change: Q∝N H∝N² P∝N³
Diameter change: Q∝D H∝D² P∝D³
Gotcha: the diameter law is exact only for small trims (< 10%). Beyond that, hydraulic similarity breaks down and the curve must be re-tested. This is a common source of off-design surprises after impeller modifications.
Specific speed
| PT | EN | ES |
|---|---|---|
| Rotação específica (Ns) | Specific speed (Ns) | Velocidad específica (Ns) |
Dimensionless parameter characterizing impeller geometry:
Ns = N × √Q / H^(3/4)
(units vary by region — US, EU, and Brazilian conventions differ).
Used to classify impeller types: low Ns → radial flow (high head, low flow); high Ns → axial flow (low head, high flow).
Gotcha: the numerical value of Ns differs by ~13% between US customary and SI calculations because of unit conventions. Always state the unit system when quoting Ns.