🔴 NPSH Calculator (Net Positive Suction Head)
Verify Net Positive Suction Head available (NPSHa) and compare against NPSHr to avoid cavitation. Features interactive installation schematics, open/closed reservoir configurations, and water property lookup.
⚡ Fortran 90 Engine
Double Precision (IEEE 754)
✓ ISO / ASME Validated
Fluid Mechanics
📊 Solver Telemetry
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390
📦 Fortran Code
4.4 KB
📅 Released
Jun 2026
⏱️ Latency
< 1 ms
📋 Sizing Parameters
Units:
SI Metric (m, kPa, °C)
Reservoir Type:
Open to Atmosphere ($P_{atm}$)
📊 Sizing Results
NPSH Available vs Required
meters
0.0
NPSH_R
20.0
NPSH Available (NPSHa)
—
m
Safety Margin
—
m
Safety Ratio
—
—
NPSH Check OK
NPSH available is safe and meets cavitation guidelines.
NPSH Sizing Equations:
• $NPSH_A = \frac{P_s - P_v}{\rho \cdot g} + z - h_f - h_v$ (Metric)
• $NPSH_A = \frac{144 \cdot (P_s - P_v)}{\rho} + z - h_f - h_v$ (Imperial)
• Margin = $NPSH_A - NPSH_R$
• $NPSH_A = \frac{P_s - P_v}{\rho \cdot g} + z - h_f - h_v$ (Metric)
• $NPSH_A = \frac{144 \cdot (P_s - P_v)}{\rho} + z - h_f - h_v$ (Imperial)
• Margin = $NPSH_A - NPSH_R$
📘 Calculation Methodology: Net Positive Suction Head (NPSHA vs NPSHR)
Mathematical Model & Theory
NPSHA measures the absolute stagnation pressure margin above fluid vapor pressure at the pump suction impeller inlet, preventing destructive vapor cavity cavitation:
$$NPSHA = \frac{P_{suction,abs} - P_v}{\rho g} = \frac{P_{tank,abs}}{\rho g} + z_{static} - h_{friction} - \frac{P_v}{\rho g}$$
$$\text{Cavitation Prevention Criterion: } NPSHA \ge NPSHR + \text{Margin (typically } \ge 0.6 - 1.0\text{ m)}$$
Assumptions
- Steady liquid flow from suction reservoir to pump nozzle.
- Friction losses $h_f$ computed via Darcy-Weisbach.
Academic References
- Hydraulic Institute (HI 9.6.1): NPSH Margin Guidelines.
- Karassik, I. J. et al.: Pump Handbook, McGraw-Hill, 4th Edition.
Worked Engineering Example
Problem Statement:
A pump draws water at $80^\circ\text{C}$ ($P_v = 47.4\text{ kPa}$, $\rho = 971.8\text{ kg/m}^3$) from an open atmospheric tank ($P_{atm} = 101.3\text{ kPa}$). The liquid level is $z = +2.5\text{ m}$ above the pump center with suction line friction head loss $h_f = 0.8\text{ m}$. Calculate NPSHA.
Step-by-step Solution:
1. Pressure heads: $h_{atm} = 101,300 / (971.8 \times 9.81) = 10.63\text{ m}$; $h_v = 47,400 / (971.8 \times 9.81) = 4.97\text{ m}$.
2. $NPSHA = 10.63 + 2.5 - 0.8 - 4.97 = 7.36\text{ m}$.
Final Result:
Available suction head is $NPSHA = \mathbf{7.36\text{ m}}$ (safe operation for pumps with $NPSHR \le 6.5\text{ m}$).
A pump draws water at $80^\circ\text{C}$ ($P_v = 47.4\text{ kPa}$, $\rho = 971.8\text{ kg/m}^3$) from an open atmospheric tank ($P_{atm} = 101.3\text{ kPa}$). The liquid level is $z = +2.5\text{ m}$ above the pump center with suction line friction head loss $h_f = 0.8\text{ m}$. Calculate NPSHA.
Step-by-step Solution:
1. Pressure heads: $h_{atm} = 101,300 / (971.8 \times 9.81) = 10.63\text{ m}$; $h_v = 47,400 / (971.8 \times 9.81) = 4.97\text{ m}$.
2. $NPSHA = 10.63 + 2.5 - 0.8 - 4.97 = 7.36\text{ m}$.
Final Result:
Available suction head is $NPSHA = \mathbf{7.36\text{ m}}$ (safe operation for pumps with $NPSHR \le 6.5\text{ m}$).