G1/4 M X F Non-Return Valve - LE-4891 13 13 Stainless steel non-return valves allow fluids to pass in one direction whilst blocking flow in the other direction. Robust and extremely compact, they are suitable for use as a safety item in all fluids circuits. They are ideal for use in severe conditions and in aggressive environments. Operation: A stainless steel valve blocks the fluid passage, when the pressure differential is lower than 0.25 bar.