Common Failures of Butterfly Check Valves

The common failures and damages of butterfly check valves in actual production are analyzed, and the original butterfly check valve structure is simulated, analyzed and verified by finite element simulation software; the structure is improved for weak parts. The valve disc is subjected to stress and deformation analysis, and a structural form with uniform force distribution and small deformation is designed, and a solution to failures is proposed.
 
1 Overview      
The large-diameter pipeline is usually used as the main pipeline of the water supply system, responsible for the production water supply of the entire system, and plays an important role in production activities. The failure of large-diameter pipelines will seriously affect production, and will be accompanied by great economic losses. In addition, the main water supply pipeline has many branches and large coverage, so it is inconvenient to close the pipeline and perform maintenance. Therefore, the stability and reliability of the operation of various valves on the main water supply pipeline are particularly important. The butterfly check valve plays an important role in the pipeline system, and its working performance and service life will directly affect the safe operation of the entire pipeline system.
 
2. The analysis of the failure
The ring water pump station of a concentration plant is equipped with a circulating water pipeline, and the butterfly check valve in the pipeline system is often damaged. The operating medium of the system is circulating water, with 7 ring water pumps working in parallel; 4 of them are working and 3 of them are idle. The rated flow of a single ring water pump is 3700m3/h, and the rated lift is 44m; the output water volume of the pumping station is 11000m3/h. The outlet pressure is 0.4MPa. The butterfly check valve is installed between the ring water pump and the electric butterfly valve. The main function is to prevent the pump station or water pump from suddenly losing power, causing a backflow of media and forming a water impact on the water supply system. The average operating cycle of the butterfly check valve is about 6 months, and the failure of the butterfly check valve will seriously affect the stable operation of the system. The main failure form of the butterfly check valve is that the valve disc falls off, causing the valve to fail. The failure of the butterfly check valve in practical engineering applications is shown in Figure 1.
 

(a) The falling of the valve disc in the pipeline system

(b)The butterfly check valve being overhauled

Figure 1 The failure of the butterfly check valve
 
It can be seen from Figure 1, the damaged part of the butterfly check valve in the practical application of the project is mainly the connection part between the valve disc and the positioning rod. Figure 1(a) shows that the connection between the disc and the valve stem is damaged, resulting in the disc of the butterfly check valve falling off in the pipeline system. If the valve disc falls off, it is easy to block the pipeline, which seriously affects the stable operation of the pipeline system. Figure 1(b) shows the damage to the connection between the valve disc and the valve stem after the butterfly check valve is overhauled. The damage is caused by stress concentration, which is fatigue damage and not caused by corrosion and other reasons.
 
In practical engineering applications, the damage to butterfly check valves is caused by the following reasons:
(1) Under the impact force of the medium, the contact area between the connecting part and the positioning rod is too small, resulting in stress concentration per unit area, and the butterfly check valve is damaged due to excessive stress value.
(2) In actual work, if the pressure of the pipeline system is unstable, the connection between the disc of the butterfly check valve and the positioning rod will vibrate back and forth around the positioning rod within a certain rotation angle, resulting in friction between the disc and the positioning rod, which aggravates the damage of the connection part.