The "lifeline" of the steam turbine - Viti exhaust check valve

In the thermal system of thermal power plants, there is a type of valve that, although not eye-catching, shoulders the responsibility of being the "ultimate defense line" for protecting the safety of steam turbines - this is the exhaust check valve, also known as the exhaust non-return valve.

I. Why is the suction check Valve so Important?

The exhaust check valve is installed on the exhaust pipelines of each stage of the steam turbine, close to the exhaust outlet. Its core function is like a "one-way door" : only allowing steam to flow from the steam turbine to the heater, and quickly and forcibly cutting off the reverse flow when necessary to protect the safety of the steam turbine body. Its existence is almost entirely aimed at preventing two major serious accidents:

When the unit suddenly loads off, the high-pressure steam in the extraction pipe and the heater will flow back into the steam turbine in the opposite direction, driving the rotor to rotate continuously and causing the speed to soar - this is the devastating "overspeed" accident.

2. To prevent water from entering the steam turbine, if the heater tube bundle breaks, water will rush into the steam turbine along with the backflow steam. When a high-temperature rotor suddenly encounters cold water, it will generate huge thermal stress, causing the rotor to bend or even be scrapped, which is known as a "water shock" accident. The function of the exhaust check valve is to close rapidly at the moment of an accident (in milliseconds), blocking the reverse flow path - it is the last mechanical defense line to protect the steam turbine.

Ii. Technical Core: Life-and-Death Speed within 0.5 seconds

The suction check valve is different from the ordinary check valve. It has extremely high requirements for closing speed and reliability.

• Quick closing: The industry generally requires that the time from receiving the signal to fully closing the valve be less than 0.5 seconds. It must be forced to drive by an external power system (pneumatic or hydraulic), rather than relying solely on medium reflux.

• High sealing performance: After closing, it must achieve zero leakage or extremely low leakage, truly playing an isolation role. The sealing surface is usually surfacing with cobalt-based hard alloy, which is wear-resistant and ensures reliable sealing.

• Low flow resistance design: During normal operation, when the valve is fully open, the pressure drop of steam should be small to reduce energy loss and improve the efficiency of the unit.

Iii. W&T Air Extraction Check Valve: German technology, strictly guarded

Viti Fluid Control has been deeply engaged in the field of power station valves, providing a full range of suction check valves that comply with ASME standards, including lift and swing structures.

Core parameters and performance of W&T air extraction check valve

Structural features and reliability design

1. Forced closing mechanism: The pneumatic/hydraulic actuator works in coordination with the counterweight, ensuring a sensitive and reliable closing response. When the medium flows in the forward direction, the cylinder intake and the counterweight jointly keep the valve disc fully open. When the reverse flow signal is triggered, the cylinder depressurizes rapidly and the valve disc closes forcibly within 0.5 seconds.

2. Hard alloy surfacing on the sealing surface: The sealing surface is surfacing with cobalt-based hard alloy, which has excellent wear resistance and ensures stable and reliable sealing.

3. Inclined valve seat design: The sealing surface of the valve seat is inclined at a certain Angle to reduce the closing time, alleviate the impact, and protect the equipment.

4. Movable valve disc structure: The valve disc is movably connected to the rocker and can automatically align with the valve seat to ensure a precise fit of the sealing surface.

5. Low flow resistance design: The streamlined design of the valve body's inner cavity ensures a large flow capacity and low pressure loss during normal operation.

 Iv. Performance Testimony

The Viti air extraction check valve has been successfully applied in multiple thermal power projects. In the heating renovation project of the 2×1000MW ultra-supercritical unit of Guoneng Lingwu, the pneumatic check valve (with a closing time of ≤0.5 seconds) supplied by Vitai, in coordination with the electric shut-off valve and the hydraulic quick-closing regulating valve, provided a complete valve solution from "control" to "protection" for the unit's steam extraction system.

W&T - With German technological heritage and experience in harsh working conditions, it provides safe, reliable and fast-response protection for the extraction systems of thermal power units.