What is NPSH? Why is it important for water pump system design?

NPSH or Net Positive Suction Head is the energy or pressure required for the operation of a water pump on the suction side to prevent the liquid from changing state into vapor, which is the main cause of cavitation that damages the water pump. Calculating the correct NPSH value is the most important thing for designing a water pump system to work efficiently, smoothly and durable. So we must get to know what NPSH is?

Generally, NPSH values ​​are divided into two values: NPSHa and NPSHr.

Why is NPSH Important?

Prevent Cavitation:

Cavitation causes pump malfunctions, noise, and damage to internal pump components.

Choose the Right Pump:

Knowing the NPSH value helps select the right pump for your system and application.

Pump System Design:

Whether its pipes, valves, or other components related to a pump, NPSH should be considered for efficient operation and long-term service.

Troubleshooting:

If a pump is experiencing problems, checking the NPSH value and improving the piping system may help resolve the issue.

NPSH is divided into two main components:

1. NPSHa (Net Positive Suction Head Available):

This is the actual pressure the pump will receive from the system. The NPSHa value depends on several factors, such as water level height, air pressure, liquid temperature, and suction line friction.

2. NPSHr (Net Positive Suction Head Required):

This is the minimum pressure the pump requires to prevent cavitation. The NPSHr value is specific to each pump and is not subject to change.

Choosing the Right Water Pump

To ensure efficient and safe water pump operation, select a pump with an NPSHr rating lower than the system's NPSHa. If the NPSHa is lower than the NPSHa, it may be necessary to upgrade the piping system, lower the pump height, or replace it with a lower NPSHr model.

         NPSH is a very important value when selecting and operating a water pump, especially a centrifugal pump. Understanding NPSH and its influence on NPSH can help us select the right pump and prevent problems that may arise during pump operation.

1. NPSHa (Net Positive Suction Head Available)

• This is the "actual suction pressure available" at the pump installation point. It reflects the properties of the entire "pipe system" we design and install. NPSHa can vary and is dependent on several factors, such as:

• Water Level Height: The higher the water level above the pump location, the higher the NPSHa value.

• Atmospheric Pressure: The higher the elevation above sea level, the lower the atmospheric pressure, resulting in a lower NPSHa value.

• Liquid Temperature: The hotter the liquid, the greater the pressure required to prevent vaporization (lower NPSHa).

• Suction Pipe Friction: Long, small, or elbowed suction pipes create resistance and lower NPSHa.

2. NPSHr (Net Positive Suction Head Required)

This is the "minimum suction pressure required by the pump" to prevent cavitation. It is a constant value specific to each pump model. It is determined by the manufacturer's design and cannot be changed. NPSHr can be viewed on the Performance Curve of that pump model.

Important: NPSHa must be greater than NPSHr.

The design of the water pump system requires that the NPSHa value be greater than the NPSHr, and a safety margin of at least 0.5 to 1 meter should be provided.

What happens if the NPSHa value is less than the NPSHr?

If the system pressure with the NPSHa value is lower than the required pump pressure (NPSHr), severe cavitation will occur.

This will result in:

• The pump will not draw water or deliver very little water.

• Noise and vibration of the pump body.

• Corrosion of the impeller and pump housing can occur, leading to significant damage.

  
  
  
  
  
  

  

  
  

NPSH Values ​​You Need to Know Before Installing a Water Pump

NPSH (Net Positive Suction Head) is an extremely important value for centrifugal pump installers. This is because centrifugal pumps often experience problems with poor suction, vibration, or noise, or lower than expected pump performance. All of these factors are related to NPSH.

NPSHa, or Net Positive Suction Head Available, is a value that varies depending on the centrifugal pump installation and pipe size. The larger the pipe size, the higher the NPSHa value.

NPSHr, or Net Positive Suction Head Required, is a measure of the pump's suction performance. It is the minimum pressure required at a specified flow rate and rated speed of the selected pump to prevent cavitation. This value is determined by the pump manufacturer and cannot be changed.

Precautions for cavitation in centrifugal pumps

              Cavitation is a reaction that gradually turns water into vapor, creating low-pressure vacuum bubbles that burst, generating shocks that can corrode and damage the impeller material. This also reduces the efficiency of water flow. If the calculated NPSH value is greater than NPSHr.

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