A system for supplying fluids to a plasma arc torch includes a single-gas power supply for regulating electrical power to the torch and for regulating supply of a first fluid to the torch, a flow regulator for regulating supply of a second fluid to the torch, and a first pressure-actuated valve disposed between the flow regulator and the torch. The valve shuts off supply of the second fluid to the torch when the first valve is closed and allows the second fluid to be supplied when the first valve is open. The first valve is opened by pressure of the first fluid supplied to the torch and closed when the first fluid is not supplied to the torch. A second pressure-actuated valve may be provided in the supply line for the first fluid, which is opened by pressure of the second fluid being supplied to the torch.