The venting application is an important application in combined cycle power plants. These valves must bypass the main steam of the waste heat boiler and discharge it into the atmosphere at the beginning of operation to ensure that the unit temperature does not rise too quickly. This is done because the process pipeline has already heated up before allowing steam to flow through the turbine bypass valve to the condenser. The throttle hole of the throttling cut-off vent valve adopts a layered arrangement structure to guide the medium to achieve layered flow, effectively preventing the medium from generating disorder and vortex. The existing venting function and multi-stage throttling structure ensure that the valve can achieve venting function under full pressure difference.

The working principle of the throttling cut-off vent valve is that in this application, high-temperature main steam (high pressure/medium pressure/low pressure) is bypassed to the atmosphere, and when the ignition of the waste heat boiler starts, the pressure and temperature rise to a certain specific point. Due to the full pressure difference experienced by the control valve, the valve and downstream pipeline will generate high noise and vibration. Therefore, downstream flow limiting devices such as diffusers are usually installed. This design provides a back pressure for the valve to limit pressure drop and subsequent noise and vibration. It can also be used to reduce noise before leaving the system and being introduced into the atmosphere. The requirement for controlling valve noise is usually 85 decibels. In some cases, insulation layers can be used to meet noise requirements. However, in many applications, downstream pipeline valves do not have any insulation. The far-field noise requirement depends on the location of the factory, but generally requires 60 decibels at the fence line. Another issue besides noise and vibration is tight shut-off. Due to the fact that these valves are typically used during start-up or in the event of a factory trip, they must remain closed during normal operation. If the valve has obvious leakage, steam will be lost. Many times, the loss of steam is enough to affect the performance guarantee of the steam turbine.