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Maintenance method and steps of butterfly valve in circulating water system of power plant 2020-03-30


(I. Overview

 

Due to the large amount of cooling water used in thermal power plants, the diameter of the pipeline of the circulating water system is also quite large. The nominal diameter of the circulating water mother pipe of the 300MW unit is DN2600. The diameter is DN1800. Butterfly valve is the first choice for opening and closing and regulating valve of low-pressure large-caliber pipeline system due to its compact structure, small footprint, and good sealing.

 

DF47DH-1.0DN1800 butterfly valve has a working pressure of ≤1.0MPa and is suitable for water with a temperature of ≤50 ℃. The valve and pipeline are connected by flanges, a two-stage reduction gear is used, and the valves are arranged vertically. The valve butterfly valve is mainly composed of a valve body with a positioning block, a butterfly plate, an upper and lower valve shaft, and a transmission device.

 

The working principle is: the motor drives the valve stem to rotate, and then drives the valve shaft and butterfly valve to rotate within 90 ° relative to the valve body to achieve the purpose of controlling flow and opening and closing.

 

Because most of the isolation valves of circulating jellyfish pipes are arranged in outdoor valve wells, the working environment in the valve wells is very poor, and the water and gas are too much, which makes the control circuit of the electric device invalid, the valve limit stops functioning, and the valve opens and closes. In actual use, the electric device should be replaced with an outdoor type to ensure that the valve can be reliably opened and closed in harsh environments.

 

(II) Maintenance of circulating water butterfly valve

 

Before the system is not isolated, the appearance of the valve can be checked: First, the water stored in the valve well is polished. Then, check the tightness of the valve's connecting flange (the pipeline should be filled with water and pressure at this time), and the flange of the valve should be tightly connected without leakage.

 

After the system is reliably isolated, the valve can be overhauled. The maintenance steps are as follows:

 

(1) First, make sure that the water stored in the pipeline has been exhausted.

 

(2) Electricly open the valve to the fully open position and pull the power supply.

 

3 (3) Workers enter the pipeline through the manhole door of the condenser (ensure sufficient lighting), and check the sealing surface of the valve. At this time, there should be no special supervision outside the manhole door, and they should be contacted in time and must not leave. The lighting in the pipeline should use 12V running lights or explosion-proof power supply to ensure personnel safety.

 

(4) If it is found that the valve seal is seriously damaged, replace the seal. First prepare spare parts of the same type of seal ring, then remove the original seal ring screw, remove the bead, remove the damaged seal ring, install the spare seal ring in place, and replace the seal ring bead and bolt.

 

After the seal ring is inspected for no damage and the valve is well sealed, the valve power can be sent on to check the high and low limit of the valve. At this time, someone should stay in the pipeline to observe the movement of the valve limit (especially the lower limit). If the valve limit is not accurate, it should be re-calibrated.

 

(5) The calibration of the valve is good. After the switch is normal, the personnel evacuated and took out the tools, the manhole door was replaced, and the valve inspection was completed.


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