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The meaning of VV valve is: Vent Valve. When the unit operates at low load with the intermediate-pressure cylinder used for startup, no steam enters the high-pressure cylinder or only a small amount does, and the high-pressure exhaust check valve remains closed. This situation can cause the high-pressure stage blades to overheat due to frictional aerating. To this end, a ventilation valve was installed on the exhaust pipe of the high-pressure cylinder, leading directly to the condenser, in order to maintain the vacuum inside the high-pressure cylinder. Furthermore, after the turbine trips, this valve opens automatically, allowing the steam in the high-pressure cylinder to be quickly discharged into the condenser. This prevents the rotor from spinning too fast due to high-pressure steam leaking into the medium-pressure cylinder through the shaft seals of the high- and medium-pressure cylinders (which are under vacuum at that time). The VV valve is controlled by a gas supply valve and operates automatically. The upper part of this valve is a cylinder; when air is lost, it is lifted upward and opened under the action of a spring ； When the solenoid valve is powered, the air supply is cut off and the VV valve opens ； When the solenoid valve loses power, air is supplied; the air piston compresses the spring, causing the VV valve to close downward. 1. At the beginning of startup, when the steam parameters are low, the high and low pressure check valves do not open; a vent valve is used to provide a path for the steam, allowing it to enter the expansion tank. One minute after connection to the grid, open the check valve and close the ventilation valve. 2. During low-load operation, prevent frictional blowing that could cause the exhaust temperature to become too high, or lead to shutdown due to a high exhaust pressure ratio. 3. To prevent excessive exhaust temperature during normal operation due to insufficient opening of the high-pressure exhaust check valve, the ventilation valve can be opened. During shutdown, open the ventilation valve to quickly release the steam from the high-pressure cylinder. 4. When the medium-pressure cylinder starts up, no air is introduced into the high-pressure cylinder; the air inside it can be removed by opening the ventilation valve, thereby reducing frictional blowdown. BDV valve: Also known as the turbine accident relief valve. In units equipped with high- and medium-pressure compression cylinders, when the unit loses load, it is necessary to prevent the residual steam in the high-pressure cylinder and high-pressure steam pipes from leaking through the gaps in the high- and medium-pressure steam seals into the medium-pressure cylinder and low-pressure cylinder, as this could have an adverse effect on the unit. If these steam seal teeth wear out and the steam seal gap increases, the likelihood of the unit speeding up rises; for this reason, an emergency drain valve (BDV) is installed. When the unit trips, the BDV valve opens quickly, directing the remaining steam at the high and medium pressure steam seals directly to the condenser to prevent the unit from speeding up. The opening and closing of the emergency discharge valve are controlled by the stroke of the actuator of the medium-pressure control valve: when the stroke of the actuator of the medium-pressure control valve is ≥ 30 mm, the emergency discharge valve closes. The stroke of the hydraulic actuator for the medium-pressure control valve