A check valve comprises a housing having a ball normally disposed on a seat defined therein to prevent communication of fluid from an inlet to an outlet thereof. A torsion spring is mounted on the housing to have an end thereof engage the ball to hold it in its normally closed position and to permit opening thereof to communicate the inlet with the outlet when the level of fluid pressure in the inlet exceeds a predetermined level. In the preferred embodiment, the torsion spring is mounted on a rotary member rotatably mounted in the housing to selectively adjust the closing force applied to the ball to vary the pressure setting thereof. During assembly of the valve, a pin is secured to the housing in blocking relationship across an outlet passage to limit pivotal movement of the end of the spring and to prevent the ball from rolling therepast.