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In thermal power station, feedwater is preheated for higher overall plant efficiency. Feedwater coming from boiler feed pump will pass through a shell and tube heat exchanger, where extraction steam from turbine transfers heat to feedwater. Feedwater heater bypass valve, actually a 3-way valve, is designed to isolate high pressure feedwater heater by diverting water flow to bypass when level switch inside HP heater is triggered. It makes maintenance possible without disruption of feedwater flow into boiler.
A complete bypass system insists of one inlet valve installed upstream and one outlet valve installed downstream. There are two paths connecting them together. In normal operation, feedwater runs through heater. In bypass operation, feedwater is isolated from heater.
When feedwater is pressurized to certain level by boiler feed pump, differential pressure between the top and bottom of steam will lift plug. Changeover valve will be in a position to allow flow into feedwater heater. At the same time, passage through bypass line is closed.
When HP feedwater heater is in malfunction caused by tube rupture, weld leakage or drainage failure, level switch inside is triggered. Signal is given to actuator to push valve disc downwards to close passage to heater. Feedwater flows through inlet valve directly to outlet valve without passing through heater.
Standard: ASME/ANSIB16.34
Connection: butt weld
Pressure: PN16～PN420
Size: DN100～350
1、WCB、ZG20CrMo、Cr5Mo、ZG20CrMoV
2、25#、12Cr1MoV
3、ASTM A216 WCB、ASTM A217 WC6、ASTM A217 WC9
4、ASTM A105、 ASTM A182 F11、ASTM A182 F22
Temperature: -29℃～570℃
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