A plug valve whose chamber or bore and whose runs or port passages are fully lined with corrosion-resistant material, most preferably polytetrafluoroethylene, such valve having recesses in its runs, near their intersection with the bore,Ball Valves into which lining material distended by heat and pressure may creep, and with the valve body defining an internally-rounded concave wall or dome at the bottom of the bore. Plug ValvesThe lining material is formed within the runs so as to be under tension longitudinally between the bore and the outer ends of the runs, and the lining material extends integrally upwardly from the bore and outwardly of the valve body to define a thick collar immediately above the neck of the bore. The valve is manufactured by use of an integral hollow rubber or like forming element comprised of tubular legs,MULTI-FUNCTIONAL WATER PUMP CONTROL VALVE and is placed inside the valve body with one such tubular leg extending through each run and through the bore. Different components of a multipart mandrel are then inserted inside the tubular legs of the forming element and assembled together therewithin. Following this, the space between the rubber forming element and the inner walls of the valve body are filled with lining material, which is then compacted by resilient outer expansion of the forming element. Subsequently, the valve body and the compacted lining material are heated to coalesce or cure the latter in place. 

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