Armstrong Series S & H in-line circulating pumps are ideal for use in hydronic heating and cooling, domestic water systems, multi-stage zoning, and general industrial service. The Armstrong S & H series pumps are available with either cast iron or bronze bodies. Give us a call toll-free for help on which pump is right for your application. Body: Radially-split body can be left in the line while servicing the pump, eliminating needless disconnecting of pipes. Oversized Shaft: ARMSTRONG circulating pumps have oversized shafts of special alloy steel, machined to exacting tolerances. Shafts have integral thrust collars, heat treated to provide long life under severe duty conditions. Centrifugal Impeller: Balanced impeller of centrifugal design ensures maximum water delivery. Positive Mechancial Seal: A tried and proven method of preventing water leakage, the well-known “ARMSEAL” construction is an often imitated feature of the ARMSTRONG circulator. Made of long-lasting, hardwearing materials, it ensures many years of noise-free, trouble-free service. Modular Construction: Armstrong Models S-25 through S-57 and H-32 through H-54 feature the unique ARMSTRONG shaft and bearing module which fits all of these models for ease of serviceability and reduced inventory costs.