Differential relief valve for a flexible underwater pipeline

摘要

A main valve (10) is held closed by a main spring (40) loaded with a preset force. A second coaxial valve (27) is closed on a seat by a second spring (35) loaded with a lower preset force. The second valve does not seal closed on its seat so bubbles of gas form a barrier to water or solid particles entering the internal chamber. The ratio of first and second valve forces is less than 4 One side of the valve is submitted to an external pressure (Pe) and the other side to an internal pressure (Pi). The valve has a valve body (1) with an upper part connected to the outside via at least one upper communication passage (25) and a lower part connected to at least one annulus of the flexible pipeline via a communication line (7). An internal chamber (3) in the valve body is at a chamber pressure (Pc). A cover (23) is mounted over the top of the valve body and contains the upper communication passage and the seat (32) for the second valve. The second valve has a top with a conical section which presses on a conical seat and the little spring presses at one end on an internal shoulder in the cover and at the other on a piece fixed to the bottom of the valve. The load on the little spring is around 0.3 daN. The seal (19) is toroidal and presses on a conical part of the first valve seal at the bottom of the valve body. The valve body of the first valve has a bottom part fixed at least part in a deflector. The little spring is placed inside the main spring. The load on the main spring is around 0.9daN. The top of the second valve and the matching seat are flat.