Abstract: Pressure can build up on one side of a valve bore sealing mechanism when it is closed. This can make the mechanism difficult to open. A bore network is provided which extends through the valve housing side wall from the inlet end of the valve bore to its outlet end. The network bypasses the sealing mechanism and its sealing areas. Needle valves, operative from outside the valve, are used to open or close the network. The network can be temporarily opened to enable pressure to equalize across the closed sealing mechanism, thereby freeing the mechanism so that it can be turned.