Abstract: The present invention is directed to an unleaded free cutting brass alloy with excellent machinability, leak-tightness, reca stability, and mechanical properties, wherein the brass alloy comprises 65 to 75 weight % of copper, 22.5 to 32.5 weight % of zinc, 0.5 to 2.0 weight % of silicon, and other unavoidable impurities; wherein the total content of copper and zinc in the brass alloy is 97.5 weight % or more.

Abstract: A double-piston-effect valve includes two valve seats symmetrically arranged in two valve endcaps at two sides, respectively. A piston ring is arranged on a rear of each of the valve seats, an inner O-ring groove is provided in the piston ring along an inner circumferential direction, an outer O-ring groove is arranged in the piston ring along an outer circumferential direction, an O-ring is fitted in each of the inner O-ring groove and the outer O-ring groove, and two semi-circular notches are symmetrically provided in a protruding portion of the piston ring.