Specification - WHB Series - Stainless Steel Bellows Water Hammer Arrestors MIFAB series - WHB Series (specify size) nesting type bellows operated water hammer arrestor with male N.P.T. connection. Bellows and body casing made of Type 304 stainless steel. WHB series is certified to the PDI WH-201 Standard. Engineered to limit line system surge pressure to 150 P.S.I.G. shall be and located in accordance with manufacturer's instructions.