Abstract: A quarter-turn plug valve has an inverted and tapered frustoconical body cavity and plug. The valve body has a through-flow passage with ports opening into said body cavity. The tapered plug has a valve stem and a throughflow passage. The valve seats surround the ports and extend from the walls of the tapered valve cavity toward the plug. The plug, when seated in closed position, is in physical contact only with the annular tapered faces of the valve seats. The valve stem contains acme or square threads near the bottom to engage with a bonnet threaded at its lower end. The bonnet extends axially along the valve stem and has a projecting flange near its midpoint, which seats on a gasket placed between it and the valve body flange. When the plug is properly oriented in closed position, the adjustable bonnet is turned on the threads of the valve stem with the stem fixed until it seats on the valve body with the desired downward thrust.

Abstract: A raised hardface overlay valve seat, fused around the periphery of the port of a valve, having an inverted frustoconical body cavity and an inverted frustoconical plug inserted into said cavity in sealing engagement therewith. A major advantage of the raised hardface overlay seat is that it has a taper conforming to the taper of the plug and as a consequence, reduces the area in contact with the plug and effectively intensifies the sealing stress that can be generated between the plug and the seats by a downward force. The plug may be used with lapping compound to lap the seats, both prior to service and in the field. Sufficient space is allowed in the cavity for a substantial relap life.