US Patent 7975721 Fluid valve systems

An apparatus includes a first valve having an inlet capable of being in fluid communication with a first fluid source, an outlet capable of being in fluid communication with the inlet, and two unidirectional valves. The first valve is capable of being in a first mode in which the inlet is in fluid communication with the outlet through a first flow path, and a second mode in which the inlet is in fluid communication with the outlet through a second flow path isolated from the first flow path. The two unidirectional valves are along the second flow path.