Seal glands for butterfly valves

A butterfly valve comprising:

• a valve disc to selectively block an aperture to adjust a fluid flow through the aperture;
• a valve body including a first circumferential surface surrounding the aperture;
• a valve retainer including a second circumferential surface surrounding the aperture, the second surface substantially parallel to the first surface;
• a seal to engage the first surface and the second surface within a circumferential cavity defined by the first surface and the second surface, the seal to translate in a direction substantially perpendicular to a longitudinal axis of the fluid flow, the seal to include a first seal portion and a second seal portion, the second seal portion positioned within an internal cavity of the first seal portion, the first seal portion including a first contact portion to contact the first surface of the circumferential cavity and a second contact portion to contact the second surface of the circumferential cavity, the second contact portion thinner than the first contact portion, the second contact portion to permit elastic compression of the seal by the first and second surfaces of the circumferential cavity;
• and
• an elastic member to seal against the seal and a third surface extending between the first surface and the second surface, the elastic member to prevent process fluid leakage from the first surface of the circumferential cavity to the second surface of the circumferential cavity.

A butterfly valve comprising:

• a valve body defining a first end of a circumferential cavity, the first end including a surface substantially perpendicular to a longitudinal axis of a fluid flow path through the butterfly valve;
• a valve retainer mounted to the valve body, the valve retainer defining a second end of the circumferential cavity, the cavity to enable a seal to translate within the circumferential cavity in a direction substantially perpendicular to the longitudinal axis of the fluid flow path, a first protrusion to retain the seal being adjacent the first end of the cavity, and a second protrusion to retain the seal being adjacent the second end of the cavity, the seal to include a first seal portion and a second seal portion, the second seal portion positioned within an internal cavity of the first seal portion, the first seal portion includes a first contact portion to contact a first surface of the circumferential cavity and a second contact portion to contact a second surface of the circumferential cavity, the second contact portion thinner than the first contact portion, the second contact portion to permit elastic compression of the seal by the first and second surfaces of the circumferential cavity;
• and
• an elastic member to seal against the seal and a third surface of the circumferential cavity, the third surface extending between the first surface of the circumferential cavity and the second surface of the circumferential cavity, the elastic member to prevent process fluid leakage from the first surface to the second surface.