Compact forged carbon steel check valve to the Class 800 pressure designation, with a bolted cover and socket-welding ends. Class 800 is the intermediate class API 602 defines for socket-welding and threaded compact valves — not 800 psi.
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This is the compact forged valve used on small-bore, high-pressure lines where a cast flanged check would be oversized: a forged carbon steel body, a bolted cover over the disc, and welded or threaded ends rather than flanges. Flow lifts the disc off an integral seat and the disc returns onto it as flow decays.
Class 800 needs explaining, because it is not 800 psi and it is not an ASME B16.34 listed class. API Standard 602 says so in its own scope: 'Class 800 is not a listed class designation, but is an intermediate class number widely used for socket welding and threaded end compact valves.' The pressure it actually stands for depends on the body material and the temperature. For an ASTM A105 carbon steel body the Class 800 rating is 1973 psig (136 bar) at −29 to 38 °C, 1516 psig (105 bar) at 316 °C and 1098 psig (76 bar) at 427 °C.
API 602 permits socket-welding and threaded ends at Class 800 from DN 8 to DN 65, that is NPS 1/4 to NPS 2-1/2, with socket-welding ends to ASME B16.11 and tapered pipe threads to ASME B1.20.1. It does not permit flanged ends at Class 800 — a flanged valve in this service has to be Class 600 or Class 1500. The unit photographed has plain counterbored socket ends. Order by nominal size, end type, body forging grade and trim, and state the design temperature so the correct point on the rating curve is used.
| Pressure Class | Class 800 |
|---|---|
| What Class 800 Is | Not a listed ASME class — an intermediate class number widely used for socket-welding and threaded-end compact valves, per API Std 602 (10th ed., 2015) |
| Pressure–Temperature Rating (ASTM A105 body) | 1973 psig (136 bar) at −29 to 38 °C; 1516 psig (105 bar) at 316 °C; 1098 psig (76 bar) at 427 °C — the rating falls with temperature and changes with the body grade |
| Size Range at Class 800 | API 602 permits socket-welding and threaded ends at Class 800 from DN 8 to DN 65 (NPS 1/4 to NPS 2-1/2) |
| End Connections (unit photographed) | Socket weld — plain counterbored sockets, no thread visible |
| End Standards | Socket-welding ends to ASME B16.11; tapered pipe threads to ASME B1.20.1 (NPT), per API 602 |
| Flanged Ends at Class 800 | Not permitted — API 602 covers flanged and butt-welding ends in Class 150 through Class 1500 but excludes flanged-end Class 800; the adjacent flanged classes are Class 600 and Class 1500 |
| Cover | Bolted cover, four studs and nuts |
| Body Material | Forged carbon steel. The grade is not marked on the photographed unit; ASTM A105 / A105N is the carbon-steel forging the Class 800 rating table above is written for. |
