Ball valve

1. A ball valve for threaded connection to a check valve having a male thread and a stem head configured for mating with a surface of a ball of the ball valve when the check valve is closed, comprising:

a ball valve housing containing the ball rotatable by a stem passing through the ball valve housing;

a flange member removably secured to the ball valve housing and supporting a seal for sealing with the ball;

a stop ring positioned outward of the ball valve housing and engageable with a stop surface on the flange member;

a coupling axially removably secured to the ball valve housing, the coupling being rotatable with respect to the ball valve housing, the coupling including female threads for engagement with the male threads on the check valve; and

the stop ring and the coupling being axially connected against axial separation by a plurality of ball locking members positioned within a race in the stop ring and the coupling, the plurality of ball locking members being removable from the race independently of removal of the coupling from the ball valve housing, whereby the coupling can be removed from the flange member where the flange member is still secured to the ball valve housing.

2. A ball valve as defined in claim 1 , wherein the stop ring can rotate with respect to the ball valve housing.

3. A ball valve as defined in claim 1 , wherein the coupling is axially coextensive with at least a portion of the ball.

4. A ball valve as defined in claim 1 , including a seal for sealing the flange member to the check valve when connected together.