The nominal pressure refers to the design pressure of a component (like a valve) classified according to standards, while the working pressure is the actual pressure it experiences in its application, which must be lower than the nominal pressure.
Here's a more detailed breakdown:
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Nominal Pressure (PN): This is a numerical designation used for reference purposes. It's a convenient rounded number related to the mechanical characteristics of a component. Think of it as a pressure rating class assigned by the manufacturer. It indicates the pressure that a component can withstand under normal operating conditions. It's determined according to standardized testing and material properties at a reference temperature (often room temperature). PN is often expressed in bars or pounds per square inch (psi).
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Working Pressure: This is the actual pressure that a component or system is subjected to during its normal operation. This value must always be equal to or less than the nominal pressure to ensure safe and reliable operation. Exceeding the nominal pressure can lead to failure, leaks, or even catastrophic events. The working pressure must take into account the temperature of the fluid, the type of fluid, and any pressure surges or fluctuations that may occur.
Key Differences and Relationship:
| Feature | Nominal Pressure (PN) | Working Pressure |
|---|---|---|
| Definition | Design pressure rating of a component, classified by standard. | Actual pressure experienced by a component during operation. |
| Purpose | Provides a standardized way to compare and select components. | Determines the safe and reliable operating limits of a component in a specific application. |
| Value | Fixed value determined by manufacturer and standards. | Variable value, dependent on operating conditions. |
| Relationship | Working Pressure ≤ Nominal Pressure. The working pressure must always be less than or equal to the nominal pressure. | Nominal pressure provides the upper limit for working pressure. |
Example:
A valve with a nominal pressure rating of PN16 (16 bar) is designed to safely handle pressures up to 16 bar under specific test conditions. However, if the valve is used in a system with a fluid temperature of 150°C, the actual working pressure may need to be limited to a value lower than 16 bar to account for the reduced strength of the valve material at higher temperatures.
In summary, the nominal pressure is a rating, while the working pressure is the actual pressure the component experiences. The working pressure must always be at or below the nominal pressure to ensure safe and proper operation.
