Internally installed check valve

A closure mechanism configured to be fixed within a flow passage of a valve body of a check valve, the closure mechanism comprising:

• a closure-mechanism body configured to be oriented transversely with respect to the flow passage;
• a first-plate member configured to support a first-seal member configured for sealingly engaging the flow passage;
• a second-plate member configured to support a second-seal member configured for sealingly engaging the flow passage,
• wherein the first-plate member and the second-plate member are movably attached to the closure-mechanism body so that a first direction of fluid flow in the valve body urges the first-plate member and the second-plate member into an adjacent position to permit fluid flow in the first direction, and a second direction of fluid flow in the valve body opposite the first direction urges the first-plate member and the second-plate member into a spread-apart position to prevent fluid flow in the second direction;
• a first-biased-fixation member movably positioned at least partially in the closure-mechanism body;
• a second-biased-fixation member movably positioned at least partially in the closure-mechanism body;
• and
• at least one biasing member configured to urge the first-biased-fixation member and the second-biased-fixation member outwardly to engage a blind depression disposed on the flow passage of the valve body,
• wherein the first-biased-fixation member and the second-biased-fixation member are sized to engage the blind depression and thereby secure the closure-mechanism body in the flow passage without any additional structure securing the first-biased-fixation member and the second-biased-fixation member in the blind depression.