What Does WOG Mean on a Valve? Pressure Ratings Explained

WOG stands for Water, Oil, Gas — the three media a valve is rated to handle under non-shock cold working pressure conditions. If you've picked up a brass ball valve and seen "600 WOG" stamped on the body, that marking tells you the valve's maximum allowable pressure at ambient temperature for those three service fluids. At Apex Flow Solutions, our brass ball valves carry a 600 WOG rating, while our stainless steel ball valves are rated at 1000 WOG or 2000 WOG depending on the series — giving you a clear benchmark before you spec a valve for your system.

What WOG Means: The Full Definition

WOG is a pressure rating designation originating from the valve and fitting industry. Each letter identifies a service media the valve is tested and approved for:

  • W — Water (cold, non-shock)
  • O — Oil (non-flammable hydraulic and lubricating oils)
  • G — Gas (compressed inert or non-reactive gases; not fuel gas — see the section below)

The number preceding WOG is the maximum allowable working pressure (MAWP) in pounds per square inch (PSI) at ambient temperature — typically defined as 100°F (38°C) or below. A 600 WOG valve is rated for up to 600 PSI under those conditions.

The term "non-shock" is important. WOG ratings assume steady-state pressure, not the pressure spikes caused by water hammer or hydraulic shock. Systems with frequent pressure transients require a valve derated below the WOG stamping or specifically selected for shock service.

WOG is sometimes written as CWP (Cold Working Pressure) — the two designations are functionally identical. You will see both on valve bodies and in manufacturer datasheets.

Common WOG Pressure Ratings and Valve Classes

The table below covers the most widely used WOG ratings in commercial and industrial service, together with typical body materials and application context.

WOG Rating Equivalent CWP Typical Body Material Common Applications
125 WSP / 200 WOG 200 PSI Cast iron, bronze Low-pressure water, HVAC, general service gate/globe valves
400 WOG 400 PSI Bronze, forged brass Plumbing, light industrial, instrument isolation
600 WOG 600 PSI Forged brass, carbon steel Commercial plumbing, compressed air lines, water systems — standard brass ball valve rating
1000 WOG 1000 PSI 316 stainless steel, carbon steel Process piping, chemical lines, moderate-pressure industrial
2000 WOG 2000 PSI 316 stainless steel, alloy steel High-pressure hydraulic, oil & gas, process plant headers

Apex Flow's brass ball valve line runs at 600 WOG — the industry standard for forged brass. Our stainless ball valve catalog covers both the 1000 WOG and 2000 WOG tiers, suitable for the demanding process and industrial environments where brass would be inadequate.

WOG vs. WSP: Cold Working vs. Steam Pressure

You will often see two ratings stamped side by side on a valve — for example, 125 WSP / 200 WOG on a bronze gate valve. These are not the same number and they are not interchangeable:

  • WOG (Cold Working Pressure) — rated at ambient temperature for water, oil, or gas service.
  • WSP (Working Steam Pressure) — the maximum allowable pressure when the valve is used with saturated steam at elevated temperature.

Steam is rated lower because elevated temperature degrades the tensile strength of the body material and softens packing and seat materials. A valve rated 200 WOG may carry only 125 WSP because the combination of heat and pressure is more demanding on metallurgy and sealing components than cold-service pressure alone.

Service Rating Used Temperature Basis Why Lower?
Cold water, oil, gas WOG / CWP Ambient (≤100°F) Baseline — full material strength available
Saturated steam WSP Up to 353°F at 125 PSI Heat reduces tensile strength; seats and packing degrade faster

Ball valves with PTFE seats are generally not rated for steam service regardless of body pressure rating. If your system carries steam, confirm the valve carries an explicit WSP rating and is fitted with appropriate seats — PTFE softens above roughly 450°F and will fail under repeated steam cycling.

WOG vs. ANSI/ASME Pressure Class

A common point of confusion is equating WOG ratings with ANSI/ASME pressure classes (Class 150, Class 300, Class 600, etc.). They look similar — a Class 600 valve and a 600 WOG valve — but they measure different things.

System What It Defines Temperature Dependent? Example
WOG / CWP Single cold-service pressure limit in PSI No (ambient only) 600 WOG = 600 PSI max at ≤100°F
ANSI/ASME Class Pressure-temperature class for flanged valves per ASME B16.34 Yes — rating varies with temperature and material group Class 600 carbon steel = 1480 PSI at 100°F, 1270 PSI at 400°F

ANSI Class numbers are not pressure values in PSI — they are class designations that map to a pressure-temperature (P-T) rating table. A Class 150 flanged valve in Group 1.1 carbon steel is rated for 285 PSI at 100°F — far above what "150" might imply if you read the number as PSI.

WOG ratings apply primarily to threaded, socket-weld, and small-bore ball valves (the type used in commercial and light industrial piping). ANSI/ASME classes apply to flanged valves and large-bore industrial valves governed by ASME B16.34. When you move from threaded ball valves to flanged butterfly or gate valves, the rating language changes accordingly.

Temperature Derating: Why the Rating Drops with Heat

WOG is defined at ambient temperature. As the operating temperature rises, the allowable working pressure falls — a concept called temperature derating. This happens because:

  • Metal alloys lose tensile strength as temperature increases (yield strength drops).
  • Seat and seal materials (PTFE, Buna-N, EPDM) soften, creep, or degrade at elevated temperatures.
  • Thermal expansion increases stress at threaded and socket connections.

For a typical 600 WOG brass ball valve with PTFE seats, the usable pressure at 150°F may be derated to 400–450 PSI, and at 200°F may drop to 300 PSI or less depending on the manufacturer's P-T curve. Always consult the manufacturer's pressure-temperature chart rather than assuming the WOG stamp applies across all temperatures.

For detailed P-T curves and derating guidance, see our Valve Pressure-Temperature Ratings Chart.

How to Read Valve Body Markings

Industrial valves carry standardized body markings that encode critical specification data. A typical brass ball valve might read:

600 WOG — CF8M — 1½ — MSS SP-110

Breaking this down:

  • 600 WOG — maximum cold working pressure, 600 PSI
  • CF8M — casting material designation for 316 stainless steel (CF8M = cast 316 SS; CF8 = cast 304 SS)
  • 1½ — nominal pipe size (NPS)
  • MSS SP-110 — manufacturing standard (Ball Valves, Threaded, Socket-Welding, Solder Joint, Grooved and Flared Ends)

For brass valves you may also see ASTM B584 (copper alloy sand castings) or forged brass called out explicitly. Certifications such as NSF 61 (potable water), UL, or FM (fire protection) appear alongside the pressure rating when applicable.

WOG for Compressed Air and Fuel Gas

Compressed Air

A WOG-rated valve can be used for compressed air service in most cases, with one important caveat: compressed air stores substantially more energy per unit volume than liquid water at the same pressure. A catastrophic failure releases that energy explosively. Many valve manufacturers publish a separate "compressed air" pressure rating that is the same as or slightly below the WOG rating.

Provided the valve is rated for gas (the G in WOG), is properly maintained, and is operated below its rated pressure, compressed air service is generally within the valve's design intent. Confirm with the manufacturer datasheet for your specific valve model.

Fuel Gas (Natural Gas, Propane, LP Gas)

WOG does not authorize use with fuel gas. This is a critical and frequently misunderstood distinction. Natural gas, propane, and LP gas service requires valves that are specifically listed and certified to one of the following standards:

  • AGA (American Gas Association) listing
  • CSA (Canadian Standards Association) certification — specifically CSA 3.16 or equivalent
  • UL listing for gas service

A brass ball valve marked 600 WOG is not automatically approved for natural gas distribution — even if gas is listed in the WOG definition. Gas-rated valves undergo additional testing for seat leakage, body seal integrity, and stem blowout resistance specific to flammable gas service. Always use a valve with a verified gas-service certification for any fuel gas application, and verify compliance with local codes (IPC, IBC, NFPA 54).

Standards and References

  • MSS SP-110 — Manufacturers Standardization Society: Ball Valves, Threaded, Socket-Welding, Solder Joint, Grooved and Flared Ends. Covers construction, testing, and marking requirements for the class of valves most commonly rated with WOG designations.
  • ASME B16.34 — Valves — Flanged, Threaded, and Welding End. The primary standard for pressure-temperature ratings in industrial valve design; defines Class designations and P-T tables by material group.
  • ASME B16.18 / B16.22 — Cast and wrought copper alloy fittings used alongside brass valves in plumbing systems.
  • NSF/ANSI 61 — Drinking Water System Components — Health Effects. Required for valves used in potable water supply.
  • CSA 3.16 / ANSI Z21.15 — Manually operated gas valves for appliances and equipment.

Frequently Asked Questions

What does 600 WOG mean?

600 WOG means the valve has a maximum allowable cold working pressure of 600 PSI for water, oil, or gas service at ambient temperature (generally defined as 100°F or below). It is the standard pressure rating for forged brass ball valves used in commercial plumbing, compressed air, and light industrial systems. As operating temperature increases above ambient, this pressure limit must be derated per the manufacturer's pressure-temperature chart.

Is WOG the same as PSI?

The WOG number is expressed in PSI — 600 WOG equals a 600 PSI cold working pressure limit. However, WOG is a rating designation that also specifies the service media (water, oil, gas) and the temperature condition (ambient/cold), not merely a raw pressure number. A valve rated 600 WOG at 70°F may only be rated for 400 PSI at 150°F. So while WOG and PSI use the same unit, they are not interchangeable terms.

Can I use a WOG valve for natural gas?

Not without an additional gas-service certification. Although G (gas) is part of the WOG acronym, fuel gas applications — natural gas, propane, LP — require valves certified to AGA, CSA, or UL gas standards. A standard WOG brass ball valve is not listed for fuel gas distribution and should not be used in that service without a verified gas certification. Compressed inert gases (nitrogen, compressed air) are a different matter and are generally within scope of the WOG rating.

What is the difference between WOG and WSP?

WOG (Cold Working Pressure) is the rated pressure at ambient temperature for water, oil, and gas. WSP (Working Steam Pressure) is the rated pressure for saturated steam service at elevated temperature. Because heat reduces material strength and degrades seat and packing materials, WSP is always lower than the WOG rating for the same valve. For example, a valve marked 125 WSP / 200 WOG is rated at 200 PSI for cold liquid or gas service, but only 125 PSI when used with steam.

What does CWP mean?

CWP stands for Cold Working Pressure and is functionally identical to WOG. Both designations represent the maximum allowable working pressure at ambient temperature for water, oil, and gas service. Manufacturers use the two terms interchangeably — you may see one or both on a valve body or datasheet. If a valve is marked "600 CWP" and another is marked "600 WOG," they are specifying the same pressure rating under the same service conditions.

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