What is a pump system curve?

A pump system curve (or system head curve) plots the total head required by a piping system as a function of flow rate. It is the sum of static head (elevation or pressure) and dynamic friction losses that increase with flow. The intersection of the system curve with the pump performance curve defines the operating point of the pump.

How do you calculate a system curve?

The system curve is calculated using H_system = H_static + K·Q², where H_static is the static head (elevation and pressure) and K·Q² represents friction and minor losses. You can determine K from a known design point (Q, H) or from pipe properties using the Darcy-Weisbach equation.

What is a pump curve?

A pump curve is a graph showing the relationship between flow rate (Q) and pump head (H) for a given pump at a constant speed. It also typically includes efficiency, power, and NPSH curves. Centrifugal pump curves generally show decreasing head as flow increases.

What is the operating point of a pump?

The operating point is the flow rate and head where the pump curve intersects the system curve. At this point, the pump’s generated head equals the system’s required head, establishing stable operation. It determines actual flow, head, power consumption, and efficiency in the system.

What is total dynamic head (TDH)?

Total Dynamic Head (TDH) is the total equivalent height that a pump must overcome to move fluid through a system. It includes static head (elevation), pressure head, and friction losses. TDH varies with flow rate and is the y-axis of the system curve.

Static head is the constant component of system head that does not depend on flow. It includes the vertical elevation difference between liquid surfaces and any pressure difference across the system (e.g., tank pressurisation).

What is friction head loss?

Friction head loss is the energy lost due to fluid friction in pipes and fittings. It increases with the square of flow velocity (approximately) and is the dynamic part of the system curve. It is calculated using Darcy-Weisbach or Hazen-Williams equations.

Free Pump System Curve Calculator for Flow Rate & Head Loss

Pump System Curve Calculator – Pump Head, Flow & Operating Point Analysis

Determine the pump operating point by overlaying your system curve with the pump performance curve. This hydraulic system curve calculator computes static head, friction losses, and finds the exact flow and head where the pump will operate. Essential for pump selection, HVAC, plumbing, and industrial hydraulic design.

📈 Interactive Pump System Curve Calculator

Unit System:

Static Head (H_static)

Design Flow Rate

Total Head at Design Flow

System K will be calculated automatically: K = (H_total - H_static) / Q²

Pipe Length

Pipe Diameter

Roughness (ε)

Minor Loss ΣK

Static Head

Design Flow

Friction factor computed via Swamee-Jain. System K derived from Darcy-Weisbach.

Pump Performance Curve

Shutoff Head (H₀)

Coefficient (a) for H = H₀ - a·Q²

Operating Flow

Operating Head

System K

Flow	System Head	Pump Head

System Head Curve Formula

The hydraulic system curve is defined by the quadratic equation:

H_system = H_static + K · Q²

H_static – static head (elevation + pressure), constant. K – system resistance coefficient, derived from pipe friction and minor losses. Q – flow rate. The term KQ² represents the dynamic (friction) losses that grow with flow.

Pump Performance Curve

A centrifugal pump curve typically shows head decreasing as flow increases, following H = H₀ - a·Q² (approximate). Actual curves also display efficiency, power, and NPSH. The best efficiency point (BEP) is where the pump operates most efficiently – ideally near the operating point.

Pump Operating Point

The operating point is the intersection of the pump curve and system curve. At this flow, the pump head exactly matches the system required head. This point determines actual pump flow rate, head, and power draw.

Worked Engineering Examples

Example 1: Chilled Water HVAC System

Static head: 10 m, design flow: 25 L/s at 32 m total head. System K = (32-10)/25² = 0.0352. Pump curve: H₀=45 m, a=0.025. Operating point solves 10+0.0352Q² = 45-0.025Q² → Q ≈ 23.8 L/s, H ≈ 30.1 m.

Example 2: Irrigation Booster Pump

Static lift: 25 ft, design flow: 200 GPM at 55 ft. K = 0.00075. Pump H₀=75 ft, a=0.0006. Intersection at Q≈210 GPM, H≈50 ft.

Frequently Asked Questions

A graph of required head vs flow for a piping system. It combines static head and friction losses.

Use H = H_static + K·Q². Determine K from one known operating point or pipe properties.

The flow and head where the pump curve and system curve intersect. It defines actual pump performance in that system.

The curve shows head delivered at various flows. Find your system curve intersection to read operating head and flow.

The total head a pump must overcome: static lift + pressure head + friction losses.

Mismatch leads to inefficient operation, cavitation, or insufficient flow.

The height difference between water levels plus any pressure difference, independent of flow.

Use Darcy-Weisbach: h_f = f·(L/D)·(V²/2g) plus minor losses.

Relates flow, head, and power with speed: Q∝N, H∝N², P∝N³. Used for VFD control.

Yes, add flows at the same head to combine parallel pump curves.

Anglian P.H.E. Footer — Fully Responsive