BYPASS VALVE CLOSING MEANS

摘要

This invention relates particularly but not exclusively to the secondary mea ns 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 th e 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.