There are five general body styles of ball valves: single body, three-piece body, split body, top entry, and welded. The difference is based on how the pieces of the valve—especially the casing that contains the ball itself—are manufactured and assembled. The valve operation is the same in each case.
Ball valves are available in sizes up to 2 inch generally come in single piece, two or three piece designs. One piece ball valves are almost always reduced bore, are relatively inexpensive and generally are throw-away. Two piece ball valves are reduced sometimes called standard bore, they can be either throw-away or repairable. The 3 piece valve is designed to be repairable. This design allows for the center section of the valve containing the ball, stem & seats to be easily removed while still mounted to the pipeline. This facilitates efficient cleaning of deposited sediments, replacement of seats and gland packing’s, polishing out of small scratches on the ball, all this without removing the pipes from the valve body.