General working principle of vent valve
In this application, high-temperature main steam (high pressure / medium pressure / low pressure) is bypassed to the atmosphere, and when the waste heat boiler ignition starts, the pressure and temperature rise to a certain point. Because the control valve withstands the full pressure differential, the valve and downstream pipelines can generate high noise and high vibration. So downstream is usually
A current-limiting device such as a diffuser or muffler will be installed. This design provides a back pressure to the valve to limit the pressure drop and subsequent noise and vibration. It can also be used to mitigate noise before the system is introduced into the atmosphere. The control valve noise requirement is usually 85 decibels. In some cases, insulation 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 is generally 60 dB at the fence line. In addition to noise and vibration, another problem is tight shutdown. Because these valves are often used during startup or factory trip situations, they must remain closed during normal operation. If there is a significant leak in the valve, steam will be lost. Many times, the lost steam is enough to affect the turbine performance guarantee.