Underwater valves are designed to prevent water from mixing with concrete in under water concrete placing operations. Valves are simple in design, eliminating sliding, rotating, swinging and plunging parts and can be used in vertical and horizontal positions. Valves operate with low pressure, sealing around solid objects, and closing against back-flow. The valve body is reinforced with steel plies for durable use. Valve opens when air pressure is released, or when concrete pressure exceeds the holding air pressure.