A valve includes a valve body, an inlet orifice in fluid communication with a first fluid volume, an outlet aperture in fluid communication with a second fluid volume and in selective fluid communication with the inlet orifice by a first fluid flow path, an activation member axially movable relative to the valve body, and a plunger axially movable within the valve body. The plunger includes an aperture therethrough defining a second fluid flow path between the first and second fluid volumes. The valve is operable in a first mode in which fluid flow is only permitted along the first fluid flow path in response to manual actuation of the activation member. The valve is operable in a second mode in which fluid flow is only permitted along the second fluid flow path when a pressure difference between the first and second fluid volumes reaches a predetermined value.

A first member having a first lock groove and a second member having a connection hole for insertion of the first member and a second lock groove opened to an inner periphery of the hole, are connected via a lock ring having a circular section and engaging with the grooves. An outer diameter of the ring under a load-free condition is set not less than a diameter of a groove bottom surface of the second lock groove. A reduced-diameter guide hole portion for guiding the ring to the second lock groove while reducing a diameter of the ring, is adjacently disposed short of the second lock groove in an insertion direction of the first member. A depth from an inner peripheral surface of the guide hole portion to a groove bottom surface of the second lock groove is set less than a radius of the circular section of the ring.