Steam pressure reducing station, or PRV station in short, is designed to receive high pressure steam and reduce it to desired condition. PRV station is usually prefabricated assembly, which is easy to install and ready to use.
Due to excellent heat transfer efficiency, steam is widely used as heating & drying medium for various purposes, such as district network heating, plant process application in food, paper, textile, brewery, chemical, pharmaceutical, petrochemical, etc. An individual steam generator could produce steam that matches with consumer requirement (temperature, pressure, flow). But steam supplied from power plant normally has a higher pressure than what is required by downstream process. A steam pressure reducing station is a solution for this problem.
Steam pressure reducing station is more than a control valve, especially when steam varies greatly. A properly designed PRV station should have correct selection of the components, because every component is indispensable in the system.
Manual control valve could be a pilot operated valve that changes steam pressure by changing pressure applied to spring inside pilot valve. It is simple structure and small investment, but stability is not so good when steam pressure is varying.
Direct acting valve doesn’t need any external force for pressure reducing. A higher or lower pressure than setting value would act on actuator diaphragm to adjust opening of disc. Thus, downstream pressure is maintained stable. Self acting valve is featured with quick action, good sealing, convenient operation, etc.
Pneumatic or electric PRV makes remote control possible. Pressure reducing is under control by PLC or locally. Pneumatic valve could work in a harsh environment, while electric valve is featured with compact structure, precise control.
Normally, single pressure reducing station is enough for process applications. But in some cases, steam PRV station would be better in serial or parallel connection.
If ratio of system maximum and minimum flow rate is bigger than 10:1, two steam PRV station in series is worth your consideration. When steam flow is low, only one station is in operation. When consumers have higher requirement for steam, the other station will be put into operation.
When turndown ratio is higher than 10:1, pls consider serial connection. Because high steam velocity will cause erosion to valve disc and seat, create big noise.
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