Triple Offset Butterfly Valves
The triple offset butterfly valves are used for shut of and regulation purposes.
Typical applications are:
- District heating
- Liquid gases (cyrogenic service)
The body geometry is designed as the result of stress calculations according to current engineering standard and rules.
The body material is high quality steel. The seats surface is covered by a wear resistance stainless steel deposited by welding overlay. On request the seat surface can be cobered also with stellite or other special material overlays. The body design can be wafer or lug or flanged or butt welding ends type.
The disc is designed to reduce at the minimum possible the pressure drop and the cavitation effects. In full open position the disc is rotated by 90° in respect of full close position. The disc seat is made with a metallic and graphoil composite gasket that can be replaced. This sealing don't contain PTFE, rubber or other plastic components that can be susceptible to high temperatures limiting the use of the valve only in the alowable range for the body material.
The triple offset design of the disc seats permits a friction free operation and a superior tightness performance without the need of a resilient seat. This feature guarantees a long life of the seat with reduced maintance. This full metal construction of the seat make the valve inherently fire safe then the ideal choice to handle flammable fluids.
The shaft is one piece and full length type permitting to use the valve also for high differential pressure. Different shaft materials are availiable for all kind of applications or service condition. The shaft is supported by two long length bearings that reduce the torque and increase the reliability. To avoid any leakage the stem has a high finish degree and a strict diametrical clearance. The torque is transmitted from the stem to the disc means two or more keys to asure a high resistance to static and dynamic force.
The standard gasket used for sealing are in pure graphite stainless stell reinforced. This type of gasket is suitable for many diferent applications. For special applications (cryogenic gases, high corrosion acids etc.). Weko can supply special gaskets designed for the specific application or according to customer specifications.
The standard packing is made of four or more pure graphite rings with square section. The first and the last ring are reinforced with stainless steel to avoid the extrusion. Other materials like PTFE are availible on request. The graphite is always treated with special corrosion inhibitors to prevent the corrosion of ferritic stainless steel stem due to galvanic cell action. For special applications (cryogenic gases, high corrosion acids, etc.) Weka can supply special packings designed for the specific application or according to customer requirements. To meet the TA-Luft requirements, on request, Weko can supply valves with special design of stem and packing. The stuffing box housing is produced with a high finish degree and a strict clearance to guarantee a perfect tight of the packing.
The standard valves are provided bracket with ISO 5211 connection suitable to apply on the valve a quarter turn gearbox or an actuators. On request Weko can provide a full range of gearbox already assembled on the valve suitable for all service conditions. One or more keys transmit the torque from the operator to the stem.