Abstract: A pressure limit valve for well tools where a valve member is moveable between a first closed portion, an open position and a second closed position. A spring for closing the valve is separated from a locking chamber which contains locking elements. The locking elements are located in a locking chamber and are held deactivated by a release sleeve which separates from the valve member in an open position. When the valve moves to the second closed position it is locked by engagement of the locking elements with a stop shoulder. In use between closely coupled inflatable packers, the valve prevents trapped pressure between the packers from affecting operation of the packer valve.