Ball valve pressure ratings explained: CWP, WOG, PN, ASME class and union figure

Ball valve ratings are written in at least five different systems, and a single size on our industrial shelf can carry several at once — CWP 4,000 psi, 1,000 WOG, PN63. They are not interchangeable, and every one of them is tied to a temperature whether or not the marking says so. Knowing which system a number belongs to is the difference between a valve that holds and one that weeps at the stem.

/01Five rating systems.

/02Every rating has a temperature.

Metal loses strength as it heats, and polymer seats soften well before the body does. A cold rating — CWP, WOG or the ambient figure of an ASME class — is the most the valve will hold near room temperature; the allowable pressure falls as temperature rises, and the seat may set a lower limit than the body. One of our industrial listings shows the pattern plainly: a 1/2" valve at CWP 3,000 psi and, for another make of the same size, 2,200 psig at 100 °F. When the line is hot, ask for the rating at the operating temperature, not the headline figure.

/03Floating against trunnion.

In a floating ball valve the ball is held between two seats and line pressure pushes it onto the downstream seat to seal; the force on the seat rises with size and pressure, and so does the operating torque. A trunnion-mounted ball is supported top and bottom on trunnions, and spring-loaded seats press onto it, which keeps torque manageable on larger, higher-pressure valves. Our oilfield listings use floating balls on 2" valves with 206, 602 and 1502 union ends, ASME Class 150 flanges and Schedule 160 butt-weld ends, and trunnion balls on 2", 3" and 4" 1502 valves, a 3-1/8" API 6A 5M flanged valve and a 4" ASME Class 600 valve to API 6D.

/04High-pressure hydraulic ball valves.

Hydraulic ball valves isolate circuits at system pressure, and they are rated in PN or psi for oil service: on our listings PN315 (4,570 psi), PN350 (5,075 psi) and PN400 (5,800 psi), with 6,000 psi and 10,000 psi versions at some sizes. Ends are BSP parallel threads up to 1-1/2" and SAE flanges at 1-1/2" and 2" — the 2" valve is a 3,000 psi SAE split-flange design in ST52-3 steel. Match the end to the port and the rating to the circuit, and see SAE J518 Code 61 and Code 62 flanges for the flange side.

/05Ordering a ball valve.

If the job is throttling rather than isolation, a globe valve is the usual choice — ours are ASME raised-face valves from Class 150 to Class 1500. For a ball valve, give the size and end connection, the pressure and the temperature together, the fluid, and for oilfield valves the service (standard or sour) and the standard required — our listings cite API 608 for the 2" Class 150 valve, API 6D for the Class 600 trunnion and butt-weld valves, and API 6A for the 3-1/8" 5M flanged valve. Union-ended valves are rated by figure; see hammer union figure numbers.