The internal pressure-operated (IPO) circulating valve is a single-shot circulating valve which allows circulation through the workstring before trip-out and serves as a drain valve during trip-out. It can be run in cased holes or openholes and maintains a full bore through the tool. The IPO circulating valve is used in the following situations:

? When a full-opening string is needed

? When redundant backup to annulus pressure-operated circulating valves is needed

? When a limited amount of annulus pump pressure is available to operate annulus pressure tools