Short Answer:

The operating point of a pump is the point where the pump characteristic curve and the system (head–discharge) curve intersect. At this point, the pump operates under actual working conditions, providing a specific discharge at a corresponding head.

In simple terms, the operating point represents the actual performance of the pump in a system. It indicates the flow rate and head where the pump runs efficiently and stably. The correct operating point ensures the pump works smoothly, avoids overloading, and delivers the desired performance.

Detailed Explanation :

Operating Point of a Pump

The operating point of a pump is a very important concept in fluid mechanics and pump engineering. It represents the actual working condition of a pump in a hydraulic system. Every pump has its own characteristic curve, which shows the relationship between the head produced and the discharge delivered. Similarly, the system curve represents the total head required by the system for various discharges.

The intersection of these two curves—pump curve and system curve—determines the operating point. This point defines the head, discharge, and efficiency at which the pump will operate in real-life conditions.

1. Meaning of Pump Characteristic Curve
   A pump characteristic curveshows how the head developed by the pump varies with the discharge. It is drawn by performing experiments at constant pump speed. Generally, as the discharge increases, the head developed by the pump decreases due to losses.

The curve also helps to find other related parameters such as:

• Efficiency versus discharge.
• Power versus discharge.
• Head versus discharge.

This curve gives an idea of how the pump behaves under different flow conditions.

2. Meaning of System Curve
   The system curveshows the relationship between the head required by the systemand the discharge flowing through it. It depends on the layout of pipes, fittings, valves, and other components of the system.

The total head in a system consists of:

• Static head (difference in height between suction and delivery tanks)
• Frictional head (due to losses in pipes and fittings)

As the discharge increases, the frictional losses rise rapidly, so the system curve is a rising curve. It starts from the static head value and increases with discharge.

3. Definition of Operating Point
   The operating pointis defined as the point of intersection between the pump characteristic curve and the system curve.

At this point:

• The head developed by the pump equals the head required by the system.
• The discharge produced by the pump equals the discharge demanded by the system.

Hence, this is the only point at which the pump can operate stably. If any condition in the system changes (like valve opening or pipe resistance), the system curve shifts, and the operating point changes accordingly.

4. Determination of Operating Point
   The operating point is determined by plotting both curves on the same graph:

• The head–discharge curve of the pump is drawn based on manufacturer data or experiment.
• The system curve is drawn considering system resistance and static head.
• The intersection of these two gives the operating point.

From this point, the discharge (Q) and head (H) can be directly read.

5. Importance of Operating Point
   The operating point is extremely important because it tells us how the pump will actually perform in the given system. Some key reasons include:

• Ensures Efficient Operation:
  The pump should ideally operate close to its Best Efficiency Point (BEP). If it operates far from this point, efficiency drops.
• Prevents Damage:
  Operating too far from the correct point can cause problems such as cavitation, vibration, or motor overloading.
• Predicts System Performance:
  The operating point helps engineers predict flow rate and pressure under actual working conditions.
• Helps in Pump Selection:
  During design, the pump is selected so that its operating point lies near the BEP on its characteristic curve for maximum reliability.

6. Factors Affecting the Operating Point
   Several factors influence the position of the operating point:

• Pump Speed:
  If the speed of the pump changes, the pump characteristic curve also changes, which shifts the operating point.
• System Resistance:
  Changing pipe size, valve position, or system layout changes friction losses and alters the system curve.
• Fluid Properties:
  Changes in viscosity, temperature, or density of the fluid can affect both curves.
• Parallel or Series Operation:
  When pumps operate in parallel or series, the combined characteristic curve changes, which moves the operating point.

7. Operation Away from the Correct Point
   If a pump operates away from its correct operating point, several issues can occur:

• Low Discharge Side: Flow becomes unstable, and the pump may experience backflow or overheating.
• High Discharge Side: The pump may not provide sufficient head and could face cavitation or motor overload.
  Thus, maintaining operation near the correct point is crucial for long-term performance and energy savings.

8. Example for Better Understanding
   Suppose a centrifugal pump has a characteristic curve showing that at a discharge of 0.02 m³/s, it develops a head of 20 m.
   The system curve, calculated from pipe friction and height difference, also shows a required head of 20 m at the same discharge.
   Hence, this is the operating pointof the pump in that system.
   If the valve in the delivery pipe is partially closed, friction increases, shifting the system curve upward, and a new operating point forms at a lower discharge.
9. Relation with Efficiency and Power Curves
   At the operating point, efficiency and power curves can also be used to check performance.

• The best efficiency is achieved when the operating point is near the BEP.
• Power consumption is optimal at this point.
  Operating too far left or right from the BEP causes higher power usage and lower efficiency.

Conclusion

In conclusion, the operating point of a pump is the actual working condition defined by the intersection of the pump and system curves. It determines the real head, discharge, and efficiency at which the pump operates. A properly chosen operating point ensures efficient performance, prevents damage, and saves energy. Therefore, in pump design and operation, maintaining the pump close to its correct operating point is essential for safe and economical performance.