1. Overview

With the development of China 's capital construction and the implementation of national large-scale projects, the number of electric power, petroleum, chemical, urban water supply, drainage system and other valves is increasing, especially the consumption of butterfly valve is very large. The production of metal hard seal butterfly valve in China can be divided into two categories in terms of sealing structure, one is elastic hard seal structure, the other is multi-level hard seal butterfly valve. The production diameter of elastic hard seal butterfly valve is generally below DN500, and multi-level structure is adopted for large diameter. The consumption of butterfly valve below DN500 is the largest, so there are many problems encountered by users in use. Here, summarize the problems often occurred, and guide the correct installation and use

2、 Elastic structure analysis and problems

Hard seal butterfly valve with elastic structure is composed of valve body, valve plate, valve rod, elastic valve seat, pressure ring and other main parts.

Structure and function of the pressure ring: the side of the pressure ring is the sealing surface of the valve body and the sealing surface of the pipeline flange to form the sealing pair, and there are bolt holes in the side. The pressure ring is pressed by bolts to fix the valve seat, and is connected with the valve body as a whole, forming the total structure length of the valve.

Because there is a screw hole in the side of the pressure ring, the effective diameter of the sealing surface is reduced. From the user's use of the flange, most of the flat welding flange is used, and its inner diameter and nominal diameter are 10 ~ 20mm. In this way, the effective sealing surface will be reduced. If the valve is not concentric with the pipe flange during installation, it will be pressed on the bolt hole diameter by dislocation. At this time, the bolt hole diameter is exposed inside the inner hole of the pipe flange, causing leakage here. Leakage is characterized by the flow of media from the back of the pressure ring.

3、 Special flange

At present, there is no special flange standard for the flexible hard seal butterfly valve. According to the current national standard, when the standard size of the flange is unchanged, we use the socket type inner flange. The inner diameter of the flange is basically the same as the nominal diameter, so as to increase the effective sealing surface, provide convenience for installation, and ensure the normal use of the valve.

In this paper, users are reminded that when using elastic hard seal butterfly valve, the matching counter flange must be a special flange, especially the pipe flange matching with the valve body pressure ring surface must be a special flange.

4、 The arrow direction on the valve body refers to the pressure direction of the medium

Generally, the direction of the arrow cast on the valve body refers to the flow direction of the medium. After the user sees the arrow, he will install it in accordance with the flow direction and the direction of the arrow, which has become a habit. The installer is easy to accept this instruction, and there is no mistake according to the national standard. However, in the case of butterfly valves with eccentric structure, there are some problems in such installation. For example, eccentric butterfly valves are installed according to the same flow direction as the medium flow. The medium in the pipe is liquid. After the valve is closed, if the pressure in the original medium inlet direction decreases or is zero, the medium at the outlet will reverse flow. If the medium is at a high level during high-level supply, the medium will be at a high level Pressure, when the pressure is greater than the inlet pressure, the valve will bear the effect of reverse pressure, because the ordinary hard seal butterfly valve is a one-way valve, so the use is not conducive to the tightness of the butterfly valve, and there will be leakage. From the above example, it is concluded that the arrow direction of butterfly valve body refers to the pressure direction of medium. Before installation, the user should know clearly the direction of the medium pressure after the valve is closed. If the arrow direction of the free valve body is consistent with the direction of the medium pressure, the correct use can be achieved, and the tightness is kept in good condition.

5、 Precautions for acceptance of resilient hard seal butterfly valve to the user's site

It is very necessary for users to conduct sampling or full inspection for purchased valves. Sampling inspection for product quality is as follows: first, check the quality of products; second, reduce unnecessary maintenance and update of valves after installation, with high success rate of one-time installation. However, in the test of the hard seal butterfly valve, the user didn't pay attention to some places, resulting in your quality, doubt or reject as unqualified. Why? There are 4 screws, 6 screws, 8 screws and 12 screws on the pressure ring according to the diameter, and the maximum bolt diameter is not more than M10. These screws are mainly used to fix the elastic valve seat. They can not bear all the medium pressure. When the valve is installed on the pipeline, it can bear all the medium force only after being compressed by the bolts on the outer flange. Due to structural reasons, leakage occurs when there is difference in inspection and acceptance. It is common for users to inform the manufacturer of nonconformity. After communication, the products can pass the customs smoothly, and there is no problem in use. Therefore, in this case, we should pay attention to the matters for users to better understand and use the elastic hard seal butterfly valve for communication.

When testing the elastic hard seal butterfly valve, place a pressing plate which is basically the same size as the flange outer circle and the valve diameter on the surface of the pressure ring. If testing with a test press, the pressing claw shall be pressed on the pressing plate so that the pressure is evenly distributed on the pressure ring at one side of the valve body. If the blind plate is used for testing, generally the clamp type elastic hard seal butterfly valve is tested by two pieces of flange. Sometimes, for the convenience of users, only one piece of flange is used to fix the valve bolt at the bottom. At this time, the fixing screw on the pressure ring on the valve body must bear all the pressure of the medium, which has been mentioned before The screw can not bear the pressure of all media, so the valve does not leak when testing with blind plate, and it is basically the same as the actual use.