BYPASS VALVE CLOSING MEANS

摘要

This invention relates particularly but not exclusively to the secondary means for closing a bypass valve. A bypass valve (102) is provided which comprises a body (4) having a bore extending therethrough; at least one aperture (32) adapted to allow fluid communication between the bore and a chamber defined in the body (4); and at least one aperture adapted to allow fluid communication between the chamber and the exterior of the bypass valve. Fluid communication between the chamber and the bypass valve exterior is permitted when a piston (78) located in the chamber is in a first position, but is not permitted when the piston (78) is in a second position. Means for selectively exposing the piston (78) to a pressure differential which moves the piston (78) is provided. A bypass valve is thereby provided which is more reliable than conventional bypass valve equipment.