Abstract: A slow-release check valve for a pneumatic system including a compressed gas source and a pneumatic device includes a body with a proximal, supply end and a distal, power end. Supply and power couplings are mounted on the body supply and power ends respectively and are adapted for coupling with a compressed gas source and a pneumatic device respectively. The body includes a passage with a frusto-conical configuration with a minimum-diameter supply end adjacent to the supply coupling and a maximum-diameter power end adjacent to the power coupling. A ball is movably located within the passage and engages the body in a closed position. The ball is biased towards its closed position by a spring. For power operation the ball is in an open position whereby gas flows around same. Disconnecting the hose causes the ball to move to its closed position and allows compressed gas to slowly dissipate from the disconnected hose whereby fishtailing is avoided.