A check valve is a valve that by its design allows flow in only one direction. If the pressure direction in the pipe reverses, no flow or only minimal flow will occur in the reverse direction. An "isolation" valve is called that because of its use in a given design, to isolate a portion of the piping system, not because of how it's built. Similarly a "drain" valve, is for, well, draining something.
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Steve Myres, PE
Automation Solutions
(480) 813-1145
A check valve is a device that prevents flow going backward in the line past the valve. It usually has no actuator, or external valve handle. An isolation valve is usually one of a pair of manual valves installed so that a device mounted between them may be removed. Sometimes an
isolation valve may be a singlet... as when the device on the line is at the end of a header. A drain valve is a valve that is connected with one side to the process fluid and one side to drain.
