A valve assembly includes a valve body having a valve bore. A valve member is slidably disposed within the valve bore between first and second stop positions. First and second valve elements of the valve member have first and second sealing surfaces equally angled with respect to a valve member longitudinal axis. Each of the first and second sealing surfaces is oriented parallel with conical shaped first and second seat surfaces. Both first and second seat surfaces are equally angled with respect to the longitudinal axis and have an adjustable spacing such that the first sealing surface contacts the first seat surface and the second sealing surface contacts the second seat surface simultaneously in the first stop position.