... pipe has 3 layers,in which the international and external layer is made of ppr materials,while the meddle layer is stiffened ... stiffens and reinforced the pipe,and reduces coefficient of linear expansion.PPR material od external layer facilitate its hot-melting and socket ... series of pressure class,including S2,S2.5,S3.2,S4 and S5,which are designed for hot water converying system.Its ...