Abstract: A check valve 10 for a fluid passageway 12 or 14 of a pressure balancer 16 or the like, and having a base plate 40 with an opening 62 therethrough connected in the passageway 12 or 14. The underside 42 of the base plate 40 disposed in the passageway 12 or 14 to face normal flow therein and the upperside 44 facing the opposite direction. A substantially "U" shaped frame member 79 is connected on the upperside 44 of the base plate 40. The frame member 79 carries two leg members 52 and 54 extending from the upperside 44 of the base plate 40 on opposite sides of the opening 62 with a bridge member 72 carried by the leg members 52 and 54 to span the opening 62. A closure member 92 is disposed on the upperside 44 of the base plate 40 adjacent the opening 62. A spring member 80 is connected between the frame member 79 and the closure member 92 normally to urge the closure member 92 to close the opening 62 whenever the flow in the passageway 12 or 14 is less than 5 psi.