Product - VHB and VHBS Bypass Valves

​​​​​​​​​​​​​For Feedwater Heaters​

In thermal power generation the feedwater heater uses heat transfer from extraction steam to the feedwater pre-heating it, improving the overall plant efficiency. In case of a feedwater heater malfunction, it needs to be isolated using a bypass system to allow maintenance without disrupting the flow of feedwater to the boiler. This system consists of two on/off valves placed upstream and downstream from the feedwater heater, with two separate conduits connecting them. One conduit routes the feedwater through the heater, while the other bypasses it.

​Key features

  • Bodies manufactured by fully machined forgings
  • Two on/off valves
  • Three-way valves
  • Built-in water hydraulic actuation
  • Upstream (VHB) and downstream (VHBS) options


  • Protects feedwater heater steam jacket against tube rupture or leakage
  • Protects turbine extraction from 
excessive backpressure
  • Allows bypass of feedwater heater 
during peak loads to increase power output from the turbine
  • Contoured plug to minimise pressure drop of the trim
  • Improves overall plant efficiency
  • Allows maintenance without disrupting flow​

Product specification

​Valve type 
Manufactured by 
IMI CCI Sweden 
Use IMI CCI PowerSiz sizing program 
Pressure class 
Up to ANSI-4500 (higher ratings may be achieved on request) 
Actuator type 
Water hydraulic, pneumatic, electromechanical 
Leakage class 
ANSI class III (against bypass line) 
ANSI class V (against feedwater heater)
Regulatory standards



Water hydraulics

The VHB and VHBS with built in water hydraulic actuators use the water pressure supplied by the feed water pump to open and close the valve. Stroke speed is controlled using a manual control valve (9) installed in the pipe connecting the valve inlet and the bonnet. The valve can be secured in a closed position using a hand wheel installed on the yoke.
During normal mode, the valves are kept open thanks to the internal pressure from the water flowing through the heater. Dump and evacuation valves are to be kept closed. It is also recommended that the filling valve is closed at this time.
When transitioning to bypass mode, the evacuation valve should open and the filling valve should close, reducing pressure in the actuators lower chamber. This will cause the valve plugs to close against the seat, putting the valves in bypass mode. Any water in the feed water heater piping is drained by opening the dump valve.


 ​Application example

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Product - VHB and VHBS Bypass Valves