According to embodiments, a pressure relief mechanism comprises a case with an installation hole formed therein, and a pressure relief valve. The pressure relief valve comprises an insertion portion which comprising a vent path formed in an axial portion of the insertion portion and a slit formed in a peripheral wall portion of the insertion portion so as to communicate with the vent path, a pedestal portion provided at an outer end of the insertion portion, a locking portion provided at an inner end of the insertion portion and locked on an inner edge of the installation hole, and a ring-like seal member interposed between around the installation hole and the pedestal portion, the seal portion comprising an elastic member.

A hydraulic overpressure valve (1) is provided comprising a valve housing (2), a valve seat (3) located in said valve housing and having a seat center and a seat center axis (4), a cone element (5) movable relatively to said valve seat (3), said cone element (5) having a cone (6) protruding at least partly into said valve seat (3) and having a cone center axis (4), and force generating means acting on said cone element (5) in a direction towards said valve seat (3). Such a hydraulic overpressure valve should be operated with low noise. To this end said cone (6) is movable along a path of movement in which said cone center axis is kept outside said seat center axis (4).