Spirax Sarco South Africa has completed the second batch of three 250mm globe control valves for delivery to Norway. The valves are designed for shipboard application where they are used to control the flow of steam at an inlet pressure of 25bar and a temperature of 230C. The outlet pressure can be as low as 4bar and the maximum flow rate is 79 100kg/hr. The valves are produces locally, stand 1.7m tall, and weigh over a ton. In order to cope with a large pressure drop, the valves are fitted with specialised trim sets incorporating multilabyrinth energy dissipating stacks, which give bilinear system characteristics. The plugs and seats are hardened with Stellite 6 that is applied using a plasma arc process. This enables the valves to dissipate approximately 8250kW of energy. The valves are fitted with long stroke tandem piston actuators with integrated tank air fail systems. This allows a compact design that achieves shut-off better than 0.01% of rated capacity, under test conditions. Prior to installation on the oil-tankers the valves were certified by Det Norske Veritas.
