Blakeborough Controls Valves - Weir Power & Industrial - #9

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Soft seat Is specified on applications where it is desirable to have a maximum closure on the control valve. The soft seat design consists of a resilient seal ring clamped into the plug by a face ring. When the soft seal contacts the valve seat, a lip on the seat bites into the face of the seal and effectively prevents leakage through the seat. The soft seat design can be specified in both balanced and un-balanced designs. Seal Rings On balanced design valves the valve plug is designed to incorporate a seal ring which prevents leakage around the periphery of the valve plug. Depending upon the desired leakage and temperature through the valve a variety of seal rings are specified. Weir Power & Industrial First choice for power and industrial protection 9 Blakeborough CAGE TRIM VALVES BV500/1 & BV990/2 BC 5-0309 Plug designs Balanced The balanced plug design is utilised to greatly reduce fluid forces acting on the valve plug allowing economical actuation and stable control. The cylindrical plug head is drilled with balancing ports to admit pressure above the plug head. The annular leakage flow between the valve plug and cage is minimised by a sealing ring retained within a plug groove. The standard sealing rings are carbon graphite which give Class III leakage. Alternatively a ‘U’ seal can be fitted to give either Class IV or Class V leakage dependent on seating load applied by the actuator. Solid (Unbalanced) The design is used on relatively low-pressure drop and/or on-off applications. It generally requires the use of much larger actuators than would be required on the balanced plug design and in all but small valve sizes is not suited to control applications. Pilot Balanced Trim The pilot balanced plug design incorporates two plugs, the main larger diameter plug used for control and the smaller pilot situated inside the main plug significantly reduces fluid forces acting on the main plug. This design produces a high integrity metal temperature where a resilient seal would be unsuitable. Opening of the valve is by the pilot plug, which lifts from its seat prior to the main plug head. This produces a flow passage to equalise the pressure above and below the valve plug, thereby significantly reducing the fluid forces acting on the valve plug. in the closed position the inlet pressure is admitted above the plug to produce a high downward seat load and the only leakage path is across metal to metal seating. Flash-cone This plug design is specified on applications requiring a very high rangeability. At low openings the conical plug nose fits inside a matching conical seat. The plug nose has a number of circumferantial grooves, which produce a staging of the pressure drop as the flow passes between the small annular passage between the plug and the valve seat. In addition to the increased rangeability this trim also allows the valve to handle higher-pressure drops at low valve openings than can be adequately handled by a standard plug design. Carbon Ring Triple Seal Ring ‘U’ Seal