1. Nominal pressure (PN)
Nominal pressure of butterfly valve is a reference value related to the pressure resistance capacity of pipeline system components. It refers to the design given pressure related to the mechanical strength of pipeline components.
The nominal pressure of butterfly valve is the pressure resistance strength of the product (the following are valves) at the base temperature. Different materials have different base temperatures and pressure strength.
The nominal pressure, represented by the symbol PN (MPa). PN is an identification of a combination of letters and numbers used for reference related to the mechanical properties and dimensional characteristics of the piping system components.
If the nominal pressure is 1.0MPa, record it as PN10. For cast iron and copper the reference temperature is 120°C: for steel it is 200°C and for alloy steel it is 250°C.
2. Work pressure (Pt)
Working pressure of butterfly valve refers to the maximum pressure specified based on the ultimate operating temperature of each level of the pipeline transportation medium for the safe operation of the pipeline system. Simply speaking, working pressure is the maximum pressure that the system may endure during normal operation.
3. Design pressure (Pe)
Design pressure of butterfly valve refers to the maximum instantaneous pressure exerted by the pressure piping system on the inner wall of the valve. The design pressure together with the corresponding design temperature is used as the design load condition, and its value shall not be lower than the working pressure. Generally, the highest pressure the system can bear is selected during design calculations as the design pressure.
4. Test pressure (PS)
For installed valves, The test pressure of butterfly valve refers to the pressure that the valve must reach when performing pressure strength and air tightness tests.
5. Relationship between these four definition
Nominal pressure refers to the compressive strength at the base temperature, but in many cases, it does not work at the base temperature. As the temperature changes, the pressure strength of valve also changes.
For a product with a certain nominal pressure, the working pressure it can withstand is determined by the working temperature of the medium.
The nominal pressure and allowable working pressure of the same product will be different at different operating temperatures. From a safety perspective, the test pressure must be greater than the nominal pressure.
In engineering, test pressure > nominal pressure > design pressure > working pressure.
Each valve including butterfly valve, gate valve and check valve from ZFA valve must be pressure tested before shipment, and the test pressure is greater than or equal to the test standard. Generally, the test pressure of the valve body is 1.5 times the nominal pressure, and the seal is 1.1 times the nominal pressure (the test duration is not less than 5 minutes).