Specification - MIFAB MWHS Series - Piston Operated Water Hammer Arrestor with SWT Connection MIFAB - MWHS series (specify size) piston operated water hammer arrestor with hard drawn seamless "K" copper body, RYTON PPS piston with double o-rings (Parco # 5778-80) and copper SWT connection. Certified to the A.S.S.E. 1010-1996 and ANSI A112-26.1M Standards. Engineered to limit the system surge pressure to 1,500 P.S.I.G.