A check valve for an inflatable device comprising a poppet urged by a conical spring to annularly seal uniformly around its entire periphery to assure more uniform cracking pressure about its entire periphery. In one embodiment the check valve comprises a locking key to lock the valve closed irrespective of the cracking pressure that may otherwise may have cracked the valve open. In another embodiment, the check valve comprises a manual dump feature that allows rapid dumping of air from the inflatable irrespective of low cracking pressure that may exist in the inflatable.