When you look through a product brochure or look at a valve physically, do you notice markings such as PN16, Class 300, or WOG 1000? These seemingly simple symbols are a technical parameter that determines the safety and performance of a valve: valve pressure rating.
What does it mean? What are the differences between the different labels? This article will provide you with a comprehensive introduction to the valve pressure rating and provide assistance in valve selection.
What is the Valve Pressure Rating?
The valve pressure rating refers to the maximum allowable working pressure (MAWP) that can safely withstand and maintain a stable working state for a long time based on the performance of its valve body material at a specified reference temperature. It can measure the safe operation of the valve.
Why is the Valve Pressure Rating Important?
Keep System Security
The valve pressure rating directly determines whether it can withstand pressure shocks under established operating conditions. The fluids and gases in industrial pipelines are usually transported under high pressure.
If the selected valve pressure rating is lower than the actual system pressure, the sealing elements and the valve body will not be able to withstand the internal load, resulting in leakage, damage or failure. This can cause interruptions in production and may also pose a safety hazard.
Meet Industry Compliance Requirements
In industries such as petroleum, chemical, and pharmaceutical that are strictly regulated, the pressure ratings of valves are clearly defined. Correct selection of valves that meet international standard pressure ratings such as ASME, ISO or API can help meet legal requirements and avoid risks.
Determine the Upper Pressure Limit of the Pipeline System
The component with the lowest pressure rating in the entire piping system limits the maximum working pressure of the system.
If the valve has a lower pressure-bearing capacity than the pipeline or other equipment, then the safe operating pressure level of your entire system should be decided based on the rating of the valve.
Impact Cost
The pressure rating will affect the material selection and manufacturing cost of the valve. Higher pressure ratings typically require thicker walls, higher-strength materials, and more sophisticated manufacturing processes. The cost also increases accordingly.
Common Valve Pressure Rating Standards
ANSI/ASME Class
ANSI Class is derived from North America. It is widely used as a pressure rating standard in the petrochemical and nuclear power sectors worldwide. It is mainly formulated in accordance with the specifications such as ASME B16.5 and ASME B16.34.
It uses “Class” followed by a number to represent, such as Class 150, Class 300, Class 1500. You should note that this number is not a direct pressure value. It is a rating code associated with valve material, structure, and pressure-temperature resistance.
For example, Class 150 valves can actually withstand a pressure of approximately 285 psi at room temperature instead of 150 psi. Typically, the higher the Class rating number, the higher the pressure the valve can withstand.
PN (Pressure Nominal)
In Europe and in most countries where metric units are used, you will often see grades starting with “PN”, such as PN10, PN16, and PN40. The number following PN usually corresponds directly to the MAWP of the valve at room temperature (20°C) in bar.
For example, PN16 valves can be used to withstand a pressure of 16 bar. Similarly, the larger the number after PN, the higher the pressure capacity of the valve.
PN pressure rating standards are widely used in industrial production worldwide. It covers all low-pressure conditions such as building water supply and drainage, air conditioning systems, as well as high-pressure conditions like chemical processes and steam pipelines. The PN rating is the most versatile pressure rating system.
CWP、WOG
On small threaded ball valves, gate valves or valves with brass bodies, you will usually see the WOG or CWP markings.
WOG (Water, Oil, Gas)
WOG is a term that has been widely used in the valve industry for a long time. It is used to indicate the maximum working pressure of the valve at a room temperature environment, applicable to water, oil and gas. For example, 600 WOG indicates that this valve can withstand a pressure of 600 psi at normal temperature.
What you need to keep in mind is that the gases included in WOG usually refer to non-combustible and compressible gases. Meanwhile, a WOG valve does not automatically indicate that the valve has obtained certification related to the gas system.
CWP (Cold Working Pressure)
CWP is similar to WOG, both referring to the maximum working pressure that a valve can withstand under cold or normal temperature conditions. Usually, this temperature ranges from approximately -20 °F to 100 °F. 100 CWP is 100 psi. It does not specifically limit the type of medium.
SWP (Steam Working Pressure)
You may notice that both 600 CWP and 150 SWP are printed on the valve. SWP is used to describe the MAWP of the valve under high-temperature steam conditions. It is usually applicable only to saturated steam, which means the steam that is in a state of gas-liquid equilibrium.
SWP is both a pressure limit and a temperature limit. The pressure of saturated steam is strictly related to its temperature. When a valve is labeled with both CWP and SWP, you should refer to the SWP value in high-temperature steam systems.
- Carbon steel is the most commonly used material in industrial valves. The following table is the standard comparison data of the main pressure ratings for carbon steel materials under normal temperature conditions.
| ANSI / ASME Class | Approximate PN (bar) | Corresponding pressure (bar, approximately) | Corresponding pressure (psi, approximately) |
| Class 150 | PN 20 | 19 – 20bar | 285psi |
| Class 300 | PN 50 | 50bar | 740psi |
| Class 600 | PN 100 | 100bar | 1480psi |
| Class 900 | PN 150 | 150bar | 2220psi |
| Class1500 | PN 250 | 250bar | 3705psi |
| Class 2500 | PN 420 | 420bar | 6170psi |
Common Pressure Ratings of Different Types of Valves
Ball Valve
A ball valve is a type of valve that controls fluid flow by rotating a ball with holes. Due to its structural characteristics, ball valves can be applied to a wide range of conditions, from low-pressure civilian applications to extremely high-pressure industrial uses.
For brass or small-diameter stainless steel threaded ball valves, the most common pressure standards are WOG or CWP, such as 600 WOG, 1000 WOG. They are mainly used for regular water, oil and gas pipelines.
In industrial scenarios such as petrochemicals, flange ball valves strictly follow the ANSI Class system. Floating ball structures of ball valves are typically used in medium and low-pressure conditions of Class 150 and Class 300.
The ball valve with a fixed ball structure can withstand higher pressure. They can operate stably in high-pressure systems of Class 600, 900 and even Class 2500.
Butterfly Valve
The sealing form of butterfly valves limits their upper limit of pressure resistance. The ordinary soft-sealing butterfly valve, whether it is of the flanged type or the wafer type, usually has a pressure rating of PN 10, PN 16, or Class 125, Class 150. This type of butterfly valve is mainly used in HVAC and water treatment systems.
If your working conditions require higher pressure, you will need to choose a high-performance double eccentric or triple eccentric metal hard-sealed butterfly valve.This type of butterfly valve can increase the pressure resistance capacity to Class 300 or Class 600.
Gate Valve and Globe Valve
Gate valves and globe valves usually follow the same pressure rating standards to keep uniform pressure-bearing capacity throughout the entire pipeline.
In the petrochemical, power, and natural gas industries, cast steel gate valves and globe valves can comply with ANSI Class 150 to Class 2500 standards.
In small-diameter auxiliary pipelines with a diameter of less than 2 inches, there is a unique Class 800 standard for gate valves and globe valves. These types of valves are usually made of forged steel and their normal operating pressure resistance is about 1975 psi.
Check Valve
The pressure rating range of the check valve is quite wide, which can meet the requirements of civilian, industrial applications as well as special high-pressure scenarios. The pressure rating is related to the connection method of the pipeline.
For the most common flange-connected check valves, their pressure ratings should meet the design pressure and temperature requirements of the pipeline system. The commonly used pressure ratings include ANSI Class 150 – 2500 and PN 16 – 100 or higher.
Factors Affecting Valve Pressure Rating
Temperature
The valve pressure rating is not a fixed value. The most crucial influencing factor is temperature. This is because the strength of the metal materials used in valve manufacturing will significantly decrease with increasing temperature.
For instance, there is a carbon steel valve that can withstand 285 psi at normal temperature. However, when the medium temperature rises to 260°C, its safe pressure-bearing capacity may drop sharply to around 170 psi.
In extremely low temperature conditions, although the strength of the metal may increase, the material will become brittle. This will result in a decrease in the valve’s ability to withstand pressure shocks.
Materials for Valve Body and Seals
The mechanical strength and temperature resistance of different materials vary greatly. You will find that for valves of the same size, their MAWP varies when using different materials.
For example, carbon steel or stainless steel performs reliably under high-pressure conditions due to their high tensile strength and high-temperature performance. Materials such as brass and cast iron have lower pressure-bearing capabilities under high temperatures or high pressures.
At the same time, the material of the sealing parts also affects the pressure rating. Soft sealing materials are prone to deformation and failure under high-pressure conditions, while hard sealing structures can be adapted to higher pressure ranges.
Structure and Manufacturing Process
The wall thickness of the valve body, the shape of the flow channel, and the sealing structure all determine the degree of structural deformation of the valve under internal pressure. The casting quality, processing accuracy and assembly quality will also affect whether the valve can maintain its integrity under high pressure.
Connection Method
Valves with different connection methods have different sealing properties and strength under pressure conditions. Flange or welding connections usually offer higher load-bearing capacity. Threaded connections are prone to stress concentration at the root of threads under high pressure. Therefore, it is usually used in low-pressure applications.
- The table below is based on the ASME B16.34 standard and shows the MAWP of carbon steel valves at different temperatures.
| Temperature | Class 150 | Class 300 | Class 600 | Class 900 | Class 1500 | Class 2500 |
| °F (°C) | psi (bar) | psi (bar) | psi (bar) | psi (bar) | psi (bar) | psi (bar) |
| -20°F to 100°F (-29°C to 38°C) | 285 (19.6) | 740 (51.0) | 1,480 (102.1) | 2,220 (153.1) | 3,705 (255.5) | 6,170 (425.4) |
| 200°F (93°C) | 260 (17.9) | 675 (46.6) | 1,350 (93.1) | 2,025 (139.6) | 3,375 (232.7) | 5,625 (387.8) |
| 300°F (149°C) | 230 (15.8) | 655 (45.1) | 1,315 (90.6) | 1,970 (135.8) | 3,280 (226.1) | 5,470 (377.1) |
| 400°F (204°C) | 200 (13.8) | 635 (43.8) | 1,270 (87.6) | 1,900 (131.0) | 3,170 (218.6) | 5,280 (364.0) |
| 500°F (260°C) | 170 (11.7) | 600 (41.4) | 1,200 (82.7) | 1,795 (123.7) | 2,995 (206.5) | 4,990 (344.0) |
| 600°F (316°C) | 140 (9.6) | 550 (37.9) | 1,095 (75.5) | 1,640 (113.1) | 2,735 (188.6) | 4,560 (314.4) |
| 700°F (371°C) | 110 (7.6) | 535 (36.9) | 1,065 (73.4) | 1,600 (110.3) | 2,665 (183.7) | 4,440 (306.1) |
| 800°F (427°C) | 80 (5.5) | 410 (28.3) | 825 (56.9) | 1,235 (85.1) | 2,055 (141.7) | 3,430 (236.5) |
- You will see that at 500°F (260°C), the pressure resistance of Class 150 has lost about 40% (from 285 to 170 psi).
- 800°F (427°C) is typically the upper limit operating temperature for carbon steel valves.
How to Select Valves Based on Pressure Ratings?
Clarify the Working Pressure of the System
First, you need to determine the actual maximum working pressure of the piping system, including the normal operating pressure, short-term impact pressure and instantaneous fluctuation pressure. The selected valve pressure rating must be higher than this actual pressure.
In addition, we recommend setting the pressure rating to 1.2-1.5 times or more the maximum working pressure of the system to cope with pressure fluctuations or occasional pressure peaks.
Combining the Temperature to Check the Pressure Temperature Table
The valve pressure rating cannot be determined by a single value alone. You also need to refer to the temperature-pressure chart for selection. This is because the MAWP of the valve varies at different temperatures.
Material Matching
The material of the valve has a significant impact on the actual pressure it can withstand. Different materials have different resistance to pressure, corrosion and high temperature. In addition to the pressure rating being greater than the system pressure, the material of the valve also needs to be suitable for your operating conditions and medium.
Consider the Component with the Lowest Pressure Rating
During the valve selection process, you should also check the pressure rating matching of each component in the entire pipeline system. Valves, flanges, fittings, etc. form a complete working pressure chain. The MAWP of the entire system is usually determined by the component with the lowest pressure rating.
Consult Experts if Necessary
In complex operating conditions, such as corrosive media, high-temperature steam, and pressure fluctuations, we recommend that you contact the valve manufacturer or an industry engineer to confirm the selection plan. This means that the selected pressure rating is both safe and compliant with the standards in actual operating conditions.
FAQs
If the Valve is Labeled with WOG or CWP, is it also Necessary to Refer to the Pressure Temperature Table?
Yes. WOG and CWP only indicate the pressure capacity of the valve for a certain type of medium at room temperature. If the operating temperature exceeds the normal temperature range, you still need to check how the pressure-temperature capacity of this valve has changed. An increase in temperature will reduce the pressure-bearing capacity of the material.
Can Valves with Different Pressure Rating Standards (such as ANSI and PN) be Used Interchangeably?
Usually, it is not possible. The number of bolt holes, the diameter of the holes, and the center distance of the flanges with different standards are often different. You cannot install directly. If you have to connect systems of different standards, you will need to use conversion flanges or flange adapters.
Can Valves be Selected Solely Based on Standard Pressure Ratings under Vacuum Conditions?
No. The standard pressure rating is designed for internal positive pressure. The vacuum condition is a negative pressure. The valve structure must be able to withstand the compressive load caused by the external atmospheric pressure.
Vacuum valves are usually described by their vacuum level or absolute pressure range to indicate their applicability. You should choose a specially designed vacuum valve.
Final Thoughts
The valve pressure rating determines the safety upper limit of the valve under specific operating conditions. Completely understanding it means that at every stage of engineering design, procurement and on-site installation, you can make accurate judgments.
Target is a professional manufacturer of hydraulic components. We can provide you with valves of various pressure rating standards. If you have any further questions regarding the valve pressure rating, please feel free to contact us for further discussion. We are more than happy to serve you.
