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What Is a Valve Pressure Rating? Definition and Guide
Posted by Gilbert Welsford, Jr on Jan 5th 2026
Pressure ratings are important considerations when designing a system that uses valves, but they can be confusing as well. In this article, we’re going to review some fundamental definitions, then discuss some of the most common pressure rating systems and classifications that you might encounter.
What is a Valve Pressure Rating?
The valve pressure rating is the maximum pressure that a valve can withstand. More specifically, it’s the total pressure that the body and stem of the valve can handle without leaking. Pressure ratings are usually expressed in psi, bar, kPa, or class ratings, but one of the areas of confusion is how that pressure is defined.
The operating pressure is the normal pressure at which the equipment operates, while the
design pressure is the operating pressure + excess pressure that the equipment may experience during operation. The manufacturer establishes the MAWP (Maximum Allowable Working Pressure), which is the maximum pressure at which the equipment can operate. Rest pressure is the pressure at which the manufacturer tests the equipment or valve, either without leakage or at the agreed leakage coefficient. The burst pressure is the pressure at which the equipment will be irreversibly damaged. Most classifications and ratings are based on the safe working pressure.
What is the Safe Working Pressure?
The safe working pressure represents the maximum pressure at which a valve can operate continuously without risking failure or damage. It is usually set at a safety margin below the burst pressure to account for unexpected pressure spikes or variations in operating conditions.
The safe working pressure depends on several factors. These include the temperature of the fluid that is in contact with the valve. The material (e.g., bronze or stainless steel) is important because the strength of the valve is directly related to the material strength. So is the valve type, as each valve has its own characteristics, as well as the end connections (e.g., flanged, threaded, or welded).
Pressure Ratings
Pressure ratings and classifications are usually based on pressure, temperature, and the material used to manufacture the valve, much like the safe working pressure. Pressure ratings are vital when working with high-pressure valve applications or low-pressure fluid control, but they are also an important guideline for design. There are several pressure ratings and classifications, but regardless of which are used, valves should be chosen so that the valve pressure rating is higher than the system's operating pressure. Now let’s look at some of those pressure rating systems.
ASME/ANSI Pressure Classification
The ASME/ANSI classification has been established by standards (with ASME B16 being the primary one) that define the maximum working pressure based on the temperature and material used. It uses a classification number (e.g., class 150, 300, 600) instead of a direct psi value.
This valve classification number doesn’t have to match the pressure, either. For example, a Class 150 valve made of carbon steel can handle up to 275 psi at 100°F and 80 psi at 800°F, while a Class 300 valve of the same material can safely withstand pressures up to 720 psi at 100°F and 405 psi at 800°F. You’ll notice that the higher the temperature, the lower the allowable pressure. The 3” gray cast iron gate valve in the image shown below is a 125 class valve that has a non-shock pressure rating of 165 psi at 300°F, but this increases to 200 psi at 100°F.
PN Pressure Classification
A PN valve rating is based on the nominal allowable working pressure at 68°F (20°C) . This is a European/ISO valve rating, and the pressure value is expressed in bars (1 bar equals 14.5 psi) rather than psi. That means PN25 would be 25 bar, or about 363 psi. Common ratings include PN10, PN16, PN25, PN40, etc.
WOG Ratings
WOG (Water Oil and Gas) is a rating, usually in psi, that represents the maximum pressure a valve can handle when used with water, oil, or gas at ambient (or low) temperatures. Oil refers to liquids with a higher viscosity than water that also have lubricating characteristics. Note that gas refers to vaporized liquids but does not include combustible liquids. WOG ratings are based on non-shock loads. The stainless steel ball valve shown in the image below has a 1000 WOG rating, meaning it can handle 1,000 psi pressure for continuous operating conditions.
CWP Ratings
The CWP (Cold Working Pressure) rating represents the maximum allowable pressure when a valve is operating at temperatures between -20° and 100°F. A rating of, say, 200CWP means 200 psi. The ¼” stainless steel ball valve shown below has a rated working pressure of 2000 CWP (psig) rating.
Why are Pressure Ratings Important in Design?
First and foremost, valve pressure ratings and valve pressure classifications ensure safety and reliability in applications involving high pressures or extreme temperatures. They also help narrow down the variety of valve options during the design phase, making it much easier to select the correct valve for specific process conditions. Additionally, well-defined class ratings enable manufacturers and end-users to remain compliant with regulatory and industry standards.
Final Thoughts on Pressure Ratings
Pressure ratings of valves are critical to the design and safety of systems that utilize valves, whether you're using ASME pressure classifications or one of the other pressure rating systems. If you aren’t sure which classification to use or are puzzled by how to use them, contact ValveMan. Our team has the technical expertise to help you, and we offer reliable customer support that can guide you through the selection process.
Gilbert Welsford, a renowned valve industry expert and third-generation owner of FS Welsford Company, is the visionary behind ValveMan.com, a leading platform for valve-related products. Gilbert's profound understanding of fluid dynamics and precision engineering plays a pivotal role in designing and applying various valve types. Known for his collaborative approach and outstanding communication skills, he builds strong relationships across multiple sectors and consistently ensures successful project outcomes. Committed to innovation and excellence, Gilbert remains at the forefront of industry advancements, consistently delivering solutions that exceed expectations.