The flapper valve includes a flapper (27) attached to the valve actuator.

In the valve body cavity, a port of the thickened upper valve body (201) serves as the flapper valve door (202) of the flapper valve (204).

An insert assembly is used in the modular saddle flapper valve assembly which has a flapper seat, flapper valve and sleeve.

The damper (32) does not act upon the flapper valve (20) during rotation to an open position of the flapper valve (20), and acts on the flapper valve (20) during rotation to a closed position.

A flapper valve is then mounted on the rivet shaft to cover the valve orifice, and the rivet shaft is deformed to retain the flapper valve in place.

The tubular member extends though the opening the flapper valve covered.

The closing mechanism (30) can also limit an opening degree of the flap valve element (22) so as to allow the flap valve element (22) to function as a check valve (10).

A method for holding open a flapper of a flapper valve.

The closing mechanism (30) can keep the flap valve element (22) in a closed state so as to allow the flap valve element (22) to function as a gate valve.

The flapper valve assembly includes a float assembly (10) that is configured to be disposed within a valve housing.

A lock mechanism (40) is provided to a flapper valve (20).

Airflow restrictor (88) may be variable such as a flapper valve (92).

A resilient member (30) biases the flapper valve toward the closed.position.

A flapper valve preferably used in injection application in deep subterranean locations has an actuating sleeve with a seat to accept an object.

The flapper valve rod (203) is inserted into a preset hole of the multi-way-type upper valve body (201).