What does the WOG stand for on the side of a valve?

WOG stands for Water, Oil, and Gas. When you see a marking such as 200 WOG or 1000 WOG cast or stamped on a valve body, it indicates the valve's maximum allowable pressure rating for general non-shock water, oil, and gas service at ambient temperatures.

For example:

• 200 WOG = rated for up to 200 psi in qualifying water, oil, or gas service
• 1000 WOG = rated for up to 1,000 psi in qualifying water, oil, or gas service

However, WOG ratings are not universal pressure ratings for every application. Temperature, media type, valve materials, and applicable industry standards can all affect whether a valve is suitable for a specific service.

Why It Matters

Many people assume that a WOG marking tells them everything they need to know about a valve's pressure capability. In reality, it is only one part of the specification.

Misunderstanding a valve's pressure rating can lead to performance issues and safety risks in higher-pressure or elevated-temperature applications.

What Does a WOG Rating Actually Mean?

A WOG rating is a manufacturer-designated pressure rating commonly found on:

• Ball valves
• Gate valves
• Globe valves
• Check valves
• Small utility valves

The rating indicates the maximum allowable pressure for:

• Water service
• Oil service
• Gas service

under relatively normal operating conditions.

For example, a valve marked 600 WOG is generally intended to withstand up to 600 psi in qualifying water, oil, or gas applications at ambient temperatures.

The exact conditions behind the rating should always be verified using the manufacturer's published pressure-temperature data. Pressure capability often decreases as temperature increases.

A Breakdown of WOG Ratings

While common plumbing valves range from 150 to 600 WOG, the highest WOG ratings for severe high-pressure industrial and oilfield applications reach 20,000 WOG (20,000 PSI).

• Standard Commercial: 150 to 600 WOG (your standard residential, HVAC, & municipal water applications).
• Industrial Process: 1,000 to 2,000 WOG.
• Severe/Oilfield (API Spec 6A): 2,000 to 20,000 WOG.

WOG vs. Steam Ratings

One common source of confusion is the difference between WOG and steam ratings.

A valve may be marked:

• 600 WOG
• 150 SWP

In this example:

• 600 WOG applies to water, oil, and gas service.
• 150 SWP means the valve is rated for 150 psi saturated steam service.

Steam service places significantly greater demands on valve materials, packing, seals, and pressure-containing components. As a result, steam ratings are often much lower than the valve's WOG rating.

A valve should never be assumed suitable for steam service simply because it has a high WOG rating.

Does WOG Apply to Every Fluid?

No.

"WOG" is a general industry designation, not a statement that the valve is compatible with every liquid or gas. For example, a valve may be rated 1000 WOG but still be unsuitable for:

• Strong acids
• Caustic chemicals
• Chlorine service
• Oxygen service
• High-temperature applications
• Abrasive slurry service

Media compatibility depends on factors such as:

• Body material
• Seat material
• Seal material
• Temperature
• Concentration
• Pressure

Always verify chemical compatibility and manufacturer recommendations for specialized services.

Common Misconception

"I've got a ball valve marked for 1000 WOG so it should be able to handle 125 PSI Steam"

Not necessarily, as "WOG" applies only to cold, non-shock conditions (usually <100°F) and steam, at 125 PSI, might be running at 400°F. Elevated temperatures, steam service, aggressive chemicals, and other specialized applications may require substantially different ratings or materials.

While, in the case of steam, the valve body might be able to withstand the pressure, the internal seats and seals (often PTFE) can fail or melt under the higher heat.

This is why WOG markings should be viewed as one specification among many. Always consult the manufacturer's pressure-temperature chart and application recommendations before relying solely on a WOG marking.