Types of valve used in power plant & their composition

Types of valve 

• Valve is a Mechanical or electromechanical device which is used to control the flow, pressure & temperature of fluid.
• Generally Globe valve, Gate valves, Butterfly valve, diaphragm valve, needle valve, Non return valves etc used in power plant various applications.
• The materials which are directly in contact with high pressure & temperature fluid are called trim materials.
• IBR Valves materials are manufactured according to the ASME class 16.34 B
• “Y” type globe valves have minimum pressure drop as compared to normal globe valves
• WCB indicates cast carbon steel, includes the standard A 216 . Used for fluid temperature up to 425 deg C
• WC-6 indicates Chromium Molybdenum steel, includes the standard A 217. Used for fluid temperature up to 575 deg C
• WC-9 indicates Cast alloy steel, includes the standard A 217. Used for fluid temperature up to 593 deg C
• SA 105 indicates forged & SA 182 indicates forged alloy steels

Equivalent grades of valves:

1. SA 216 WCB/WCC: SA 105N
2. SA 217 WC6: SA 182 F11
3. SA 217 WC9: SA 182 F22
4. SA 217 C12A : SA 182 F91

• The MOC of Stud & nut materials of high pressure valves are SA 194 Gr.B7 & SA 194-2H
• Stem nuts of all high pressure valves is of Aluminium bronze materials
• The yoke of all high pressure valves are made up of material A-216 WCB
• Hand wheel of all HP valves are made up of SG iron 400/12
• Stems of all HP valves are made up of A 479-410-2

Comparison between Gate valve & Gate valve

• For a same size of valves, the size & weight of gate valves is more as compared to globe valves
• Time required for operating the gate valve is more as compared to globe valve
• Effort required to operate the gate valve is less as compared to globe valve
• Complicated maintenance procedure for larger size gate valves & simple maintenance procedure for globe valves
• In gate valve pressure drop of fluid is very less as compared to globe valve
• Gate valves cannot be used for flow regulating valves whereas globe valves can be used
• Very less or no turbulence of fluid in gate valves whereas there is much turbulence in globe valves
• Upon prolonged exposure of cast carbon steel or forged carbon steel valves to temperatures above 425°C, the carbide phase of steel may be converted to graphite. Permissible but not recommended for prolonged use above 425°C.