Minimum flow valve for feed water pumps: The key guardian of the "heart" of power plants

In thermal power plants, the feed water pump is hailed as the "heart" of the unit, and the minimum flow valve serves as the "protective device" for this heart. When the unit starts or stops or operates at low load, the outlet flow of the feed water pump is lower than the safety value. If the recirculation is not started in time, the water temperature inside the pump will rise and vaporize, which will cause serious cavitation damage. The minimum flow valve for the feed water pump is precisely the key equipment to prevent this problem.

I. "Survival Challenges" under Harsh Working Conditions

The minimum flow valve of the feed water pump is installed between the outlet of the feed water pump and the deaerator, bearing the largest pressure difference in the entire plant - directly reducing the high-pressure feed water from 20-30 mpa to the pressure of the deaerator (about 1MPa). Under such an extreme pressure difference, when the fluid passes through the valve at high speed, flash evaporation and cavitation erosion are very likely to occur, causing severe erosion damage to the internal components of the valve.

The practical predicament of this workstation is that, regardless of whether it is an imported brand or a domestic one, the minimum flow valve is one of the valves with the highest failure rate and the shortest lifespan in power plants.

Many power plants have to disassemble and inspect or even replace the internal components of their valves every year. Some imported valves, after years of use, no longer receive services from the original manufacturers. Even after repair, the internal leakage still cannot be completely solved, and eventually the maintenance value is lost. This pain point has become increasingly prominent as the units frequently participate in deep peak shaving - the frequency of opening and closing the recirculation valve has increased, the erosion damage has accelerated, and the internal leakage problem has become more serious.

Ii. Why do traditional structures frequently fail?

Take some imported brands as an example. The internal structure of their valves is complex - the combination of multiple parts leads to large cumulative errors, and the valve core is prone to getting stuck. The gap of the filter screen is too large to effectively intercept impurities. Although the sleeve is known as "multi-layered", its pressure-reducing principle is not sufficient, and the throttling effect is greatly reduced. The final outcome is: the valve core is scratched and stuck, the bolts are broken, the sleeve is cavitation, the sealing surface is eroded, and the valve body is even severely damaged by high-pressure water erosion.

The fundamental reason lies in the fact that under such a high-pressure difference working condition, if the number of throttling and pressure reduction stages is insufficient, the hardness of the sealing surface is not enough, and the structural anti-blocking ability is weak, no "famous brand" can last long.

Iii. Vita Solution: The Circulating Convection Disc Technology Breaks the Deadlock

Viti Fluid Control has independently developed the circulating convection labyrinth disc technology for the harsh working conditions of minimum flow valves.

Schematic diagram of the W&T circulation offset disc technology principle

    Core technical principle

After the fluid enters the disc, it collides with the wall and splits in two, consuming energy. The two fluids then meet head-on and collide again, consuming energy. This process of "impact - diversion - collision - pressure reduction" is repeated multiple times, gradually decomposing the high pressure difference step by step, and ultimately controlling the flow rate through the sealing surface within the safe range of 20-30m/s for the liquid, fundamentally eliminating the destructive power of cavitation and cavitation.

Four major technical advantages

1. Anti-clogging design: The cross-sectional area of the inlet and outlet of the disc is the same, and the flow channel is circular without dead zones, so impurities will not accumulate and get stuck

2. Anti-erosion ability: After multi-stage pressure reduction, the medium velocity on the sealing surface is significantly reduced. When combined with Stellite 6 hard alloy surfacing the sealing surface, its anti-erosion performance is far superior to that of ordinary materials

3. Pilot-operated self-sealing structure: When closed, the inlet pressure assists in pressurizing and sealing to ensure a tight cut-off, and the leakage level can reach ANSI Class VI

4. Applicable to deep peak shaving: The valve core and valve seat adopt a flat seal + cofferdam structure, effectively protecting the sealing surface during frequent opening and closing, and meeting the frequent action requirements of deep peak shaving in thermal power units

Mature cases

• Renovation of the HORA minimum flow valve for the 300,000-unit unit at Xuzhou Pengcheng Power Plant

• The renovation of the CCI minimum flow valve for the 600,000-unit unit at the Daban Power Plant of State Power Investment Corporation

• The renovation of the HORA minimum flow valve for the 600,000-unit unit at the Shangdu Power Plant of Northern United Power

Iv. State Power Investment Corporation Xinchang Power Plant: The replacement Plan has been verified again

In 2023, Viti provided a minimum flow valve technical transformation solution for the 2×700MW ultra-supercritical units of the Xinchang Power Generation Branch of State Power Investment Corporation. This factory originally used the minimum flow valve of a certain imported brand. After nearly four years of use, serious internal leakage and difficulty in starting the valve occurred. Despite multiple repairs (disassembly, grinding, and welding), no good results were achieved. The original manufacturer no longer provided services beyond the warranty period.

After on-site diagnosis by the Viti technical team, a targeted solution was provided: a circulating convection labyrinth disc assembly combined with a pilot-operated self-sealing structure was adopted to solve the problem of cavitation erosion from the source, while achieving precise regulation and tight cut-off. The plan has been officially delivered and implemented.

Viti - Provides long-life and highly reliable solutions for the recirculation system of power plant feed water pumps, safeguarding the safe beating of the "heart" of the units.