English
What does W.O.G means in Valve Field
Created on 09.21
W.O.G: Definition, Pressure Ratings, and Application Guidelines
I. Definition and Attributes of W.O.G
1. Meaning of the Letters
W.O.G is an acronym formed from the initial letters of three English words:
- W
= Water
- O
= Oil
- G
= Gas
Together, they indicate that the valve is suitable for water, oil, and gas media. These three media are the most fundamental general-purpose fluids in industrial piping. Consequently, the vast majority of general-purpose small valves (threaded ball valves, gate valves, check valves, etc.) are marked with W.O.G on the body or nameplate.
2. Attribute Definition
The complete attribute of W.O.G is a combined designation of "media applicability + maximum working pressure at ambient temperature" – not merely a material code or a pressure class code.
It is important to clarify:
- W.O.G is an
industry convention under the American standard system, not a mandatory marking required by Chinese national standards.
- Valves marked with W.O.G are designed by default for
general-purpose service conditions and are not suitable for strong acids, strong alkalis, highly corrosive media, highly toxic media, or other special services.
- W.O.G specifies only the applicable media range; it does
not restrict the valve body material. W.O.G valves are available in cast iron, carbon steel, stainless steel, copper alloys, and other materials. During selection, four parameters must be verified simultaneously: material, pressure, temperature, and medium.
II. Pressure Rating Markings and Conversions
1. Meaning of the Numbers
Common markings such as 1000WOG, 2000WOG, and 3000WOG on nameplates indicate the maximum working pressure of the valve at ambient temperature in water/oil/gas service. The unit is PSI (pounds per square inch) .
PSI is a pressure unit commonly used in European and American systems. The conversion relationships with metric units are as follows:
- Exact conversion:
- 1 PSI ≈ 0.00689476 MPa
- 1 MPa ≈ 145.04 PSI
Common W.O.G Rating Conversion Table:
W.O.G Marking | Corresponding PSI | Exact MPa | Engineering Approximation |
600WOG | 600 PSI | ≈ 4.14 MPa | ≈ 41 kgf/cm² |
800WOG | 800 PSI | ≈ 5.52 MPa | ≈ 55 kgf/cm² |
1000WOG | 1000 PSI | ≈ 6.89 MPa | ≈ 69 kgf/cm² |
2000WOG | 2000 PSI | ≈ 13.79 MPa | ≈ 138 kgf/cm² |
3000WOG | 3000 PSI | ≈ 20.68 MPa | ≈ 207 kgf/cm² |
Engineering Rule of Thumb: 1 MPa ≈ 10 kgf/cm² (kilogram-force per square centimeter). For example, 1000WOG ≈ 6.89 MPa ≈ 69 kgf/cm², often referred to in engineering as "about 70 kilograms."
The higher the number, the greater the pressure-bearing capacity of the valve under water, oil, and gas service conditions. Accordingly, the body wall thickness, sealing surface materials, and connection strength are upgraded correspondingly.
2. Temperature Basis and Applicable Range
According to MSS SP-25 (Manufacturers Standardization Society of the Valve and Fittings Industry), W.O.G/CWP ratings apply to an ambient temperature range of -29°C to 38°C (-20°F to 100°F) . Within this temperature range, the W.O.G rating is valid. Outside this range, material strength decreases, and the allowable working pressure must be reduced accordingly. The manufacturer's pressure-temperature rating table must be consulted for confirmation.
3. Relationship Between W.O.G and CWP
CWP (Cold Working Pressure) and W.O.G ratings can be considered equivalent in most cases. Both indicate the maximum pressure a valve can withstand at ambient/cold temperature and are not applicable to steam or other high-temperature services. Some manufacturers mark CWP instead of W.O.G on the nameplate; the meaning is identical.
III. Differences Between W.O.G, PN, and Class
There are three pressure rating systems for valves: European PN, American Class, and general W.O.G. Their temperature bases, application scenarios, and natures are different and must not be confused.
Comparison Item | PN (Nominal Pressure) | Class (Pound Rating) | W.O.G |
Standard System | European (GB/T, DIN, EN) | American (ASME/ANSI) | American industry convention |
Temperature Basis | 20°C (ambient) | 454°C (high-temperature basis) | -29°C to 38°C (ambient) |
Pressure Unit | bar | Unitless (class code) | PSI |
Primary Application | National standard piping / chemical / municipal | Export, American standard projects | General small valves (threaded ball valves, gate valves, check valves, etc.) |
Marking Format | PN16, PN25, PN40 | Class150, Class300 | 1000WOG, 2000WOG |
Core Differences:
- PN
is the nominal pressure rating under the European system. The number following PN corresponds to the allowable working pressure at 20°C (bar).
- Class
is the pressure class code under the American system. Its basis temperature is 454°C. Class 150 at ambient temperature actually corresponds to approximately 285 PSI, not 150 PSI.
- W.O.G
is a combined marking of media + actual working pressure, with an ambient temperature basis, and is most closely aligned with the actual service conditions of small general-purpose valves.
Key Note: W.O.G and Class cannot be directly equated. W.O.G indicates the manufacturer's actual allowable working pressure at ambient temperature, while Class indicates a pressure class code based on a high-temperature basis. The two may be referenced but are not interchangeable.
IV. Core Functions of W.O.G
1. Quick Assessment of Media Compatibility
Seeing the W.O.G marking immediately confirms that the valve is suitable for ambient-temperature, general water, oil, and gas service. If used with corrosive media such as hydrochloric acid, caustic soda, or strong oxidizers, or in special services such as high-temperature steam, abrasive slurries, or vacuum, problems such as corrosion, seal failure, and body damage are highly likely.
2. Simplified Procurement and Construction Communication
In civil, HVAC, water supply and drainage, gas, and ordinary oil piping, W.O.G is the industry's common language. Procurement and construction personnel can quickly confirm the applicable media and pressure limits of a valve upon seeing 1000WOG or 2000WOG, without repeated parameter verification.
3. Distinguishing General-Purpose Valves from Special-Purpose Valves
Conventional flanged industrial valves and national standard PN-system valves are generally not marked with W.O.G. Valves without W.O.G marking are mostly PN-system valves, steam valves, corrosion-resistant chemical valves, cryogenic valves, fire-fighting specialty valves, etc., and must be selected according to their respective standard systems. Conversely, W.O.G valves cannot be used as substitutes for special-purpose valves.
V. Selection Precautions and Usage Restrictions
1. W.O.G Does Not Mean High-Temperature Resistance
W.O.G is by default an ambient-temperature rating. Common soft-seated W.O.G valves have temperature limits as follows:
- Rubber seals: approximately -20°C to 80°C
- PTFE seals: approximately -20°C to 200°C
- (Specific limits shall be based on the manufacturer's data sheet.)
Beyond the temperature range, the pressure rating drops significantly. A 1000WOG valve at high temperature may only withstand very low pressure. Over-temperature use is strictly prohibited.
2. Conventional W.O.G Valves Are Strictly Prohibited for Steam Piping
Steam is a high-temperature medium (typically above 150°C), which exceeds the W.O.G rating's applicable temperature range of -29°C to 38°C. According to MSS SP-25, W.O.G/CWP ratings are not applicable to steam service. For steam service, valves specifically marked with WSP (Working Steam Pressure) shall be selected.
3. Distinguishing W.O.G from WSP
Comparison Item | W.O.G / CWP | WSP / SWP |
Applicable Temperature | -29°C to 38°C (ambient) | Typically 150°C to 260°C and above |
Applicable Media | Water, oil, gas (ambient) | Steam |
Pressure Characteristic | Maximum working pressure at ambient temperature | Maximum working pressure at maximum temperature |
Marking Basis | MSS SP-25 | MSS SP-25 (manufacturer's choice) |
Relationship | On the same valve, the W.O.G rating is always higher than the WSP rating. | — |
According to MSS SP-110, the difference between SWP/WSP and CWP/W.O.G is that WSP indicates the pressure at which the valve can continue to operate within the maximum temperature range, while W.O.G indicates only the pressure at ambient temperature. On the same valve, the W.O.G rating is always higher than the WSP rating.
Engineering Judgment: A bronze gate valve with a W.O.G rating of 200 PSI may have a WSP rating of only 125–150 PSI. If the steam system working pressure is 150 PSI and the safety valve is set at 165 PSI, the bronze valve is not suitable; a cast iron or steel body valve should be considered.
4. Nameplate Marking W.O.G Does Not Imply a Universal Body Material
W.O.G specifies only the applicable media range and does not restrict the valve body material. W.O.G valves are available in cast iron, carbon steel, stainless steel, copper alloys, and other materials. During selection, four parameters must be verified simultaneously: material, pressure, temperature, and medium – none can be omitted.
Appendix: Quick Reference for W.O.G-Related Markings
Marking | Full Name | Meaning |
W.O.G | Water, Oil, Gas | General service for water, oil, and gas; maximum working pressure at ambient temperature (PSI) |
CWP | Cold Working Pressure | Cold working pressure; equivalent to W.O.G |
WSP / SWP | Working Steam Pressure / Steam Working Pressure | Steam working pressure; suitable for high-temperature steam service |
WWP | Working Water Pressure | Water working pressure |
PN | Pressure Nominal | European nominal pressure rating (bar, basis 20°C) |
Class | — | American pressure class (unitless, basis 454°C) |
Contact
Leave your information and we will contact you.
WhatsApp