How To Calculate Discharge Pressure Of Positive Displacement Pump

Discharge Pressure Equation:

\[ P_{discharge} = P_{suction} + \rho g h + \Delta P_{friction} \]

Suction Pressure (P_suction):

Density (ρ):

kg/m³

Gravity (g):

m/s²

Head (h):

Friction Pressure Loss (ΔP_friction):

Discharge Pressure (P_discharge):

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1. What Is Discharge Pressure Calculation?

The discharge pressure calculation for positive displacement pumps determines the total pressure at the pump outlet by accounting for suction pressure, static head pressure, and friction losses in the system.

2. How Does The Calculator Work?

The calculator uses the discharge pressure equation:

\[ P_{discharge} = P_{suction} + \rho g h + \Delta P_{friction} \]

Where:

\( P_{discharge} \) — Discharge pressure (Pa)
\( P_{suction} \) — Suction pressure (Pa)
\( \rho \) — Fluid density (kg/m³)
\( g \) — Gravitational acceleration (m/s²)
\( h \) — Static head (m)
\( \Delta P_{friction} \) — Friction pressure loss (Pa)

Explanation: The equation sums the suction pressure, hydrostatic pressure from elevation changes, and pressure losses due to pipe friction to determine the total discharge pressure.

3. Importance Of Discharge Pressure Calculation

Details: Accurate discharge pressure calculation is essential for proper pump selection, system design, ensuring adequate flow rates, and preventing pump damage or system failure.

4. Using The Calculator

Tips: Enter all pressure values in Pascals (Pa), density in kg/m³, gravity in m/s² (standard is 9.81 m/s²), and head in meters. All values must be non-negative with density and gravity greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: Why is discharge pressure important for positive displacement pumps?
A: Discharge pressure determines the pump's ability to overcome system resistance and ensures proper fluid delivery without causing damage to the pump or piping system.

Q2: How do I determine friction pressure loss?
A: Friction loss depends on pipe length, diameter, fluid viscosity, flow rate, and pipe roughness. Use Darcy-Weisbach equation or consult engineering tables for specific applications.

Q3: What is the typical range for suction pressure?
A: Suction pressure varies by application but must be above the fluid's vapor pressure to prevent cavitation. Positive values indicate pressure, negative values indicate vacuum.

Q4: How does fluid density affect discharge pressure?
A: Higher density fluids create greater hydrostatic pressure for the same head, resulting in higher discharge pressure requirements.

Q5: When should I consider additional pressure factors?
A: For complex systems, consider additional factors like acceleration head, pressure drops across valves and fittings, and safety margins for system variations.