The device has waterproof envelopes (X, Y) for collecting a fluid which escapes from a flexible tube (7). The pressure exerted by the escaping fluid acts on a piston (22) for moving a mechanical system (Z) to close a supply valve (1) through a fork (28). The tube (7) passes in a tube (9) that is fixed to two cases (4a, 10a) by links, and is terminated at each end by the links.