I was looking into getting some ball valves for a plumbing project and I noticed that many of them have a "WOG" number. What does this mean and is it something I need to be concerned about when selecting valves?
Valves carry a variety of markings, some of which are ratings.
Common (sometimes older) ratings are WOG and WSP (or sometimes SWP). WOG stands for the water, oil, and gas rating for the valve and reflects the maximum pressure capability of the valve at 100 F.
WSP stands for working steam pressure and reflects the maximum pressure rating for the valve at the highest temperature rating.
Acceptable working pressure for all equipment decreases as temperatures increase. The WOG rating is always higher than the WSP rating for a valve or fitting.
SWP: Steam Working Pressure: This designates the maximum recommended steam pressure a product can operate at.
CWP: Cold Working Pressure: This designates the maximum non-shock pressure a product can operate at. “Cold” is generally defined as a range between -20°F to 100°F.
WOG: Water, Oil and Gas: This was an older, generic pressure rating call-out which has been largely replaced by CWP. In this designation, “Gas” refers to any non-flammable, compressible fluid in a gaseous state. It does not imply a product’s suitability or third-party approval for use with flammable gases. Similarly, in this designation, “Oil” does not imply a product’s third-party approval for use with any petroleum products.
Some valves are governed by API Spec 6A which will carry the WOG mark, and is a little broader than the above. In this spec the WOG rating is the working pressure of the valve at whatever temp class it is in. These valves come in 2,000, 3,000, 5,000, 10,000 15,000 and 20,000 WOG ratings with temperature classes from -75F to 350F.
Bottom line - yes in principle you do need to make sure the valve you select is going to have a pressure & temperature rating which meets or exceeds your requirement. But in a residential plumbing or hydronic heating situation, the pressures are normally << 100 PSI and temperatures < 180 F, so many WOG rated valves would exceed this by far.