[Science stickers] Analysis of the advantages and disadvantages of 5 valves- Kaixin Pipeline Technologies Co.,Ltd

"Know yourself and the enemy, never end in battle" The prerequisite for the correct selection and use of valves is a comprehensive and specific understanding of the advantages and disadvantages of each valve and the physical properties (temperature, pressure) of the medium used; chemical properties (corrosive); The cleanliness of the medium (there are no solid particles or viscosity, etc.), choosing the right product, can obtain its best performance and the most economical service life. Below we will analyze the advantages and disadvantages of the following valves.

NO.1

The butterfly valve is a valve that uses a disc-type opening and closing member to reciprocate about 90° to open, close and adjust the fluid channel.

advantage:

　 ①Simple structure, small size, light weight, less consumables, suitable for large-diameter valves;

②Rapid opening and closing, low flow resistance;
　 ③It can be used for media with suspended solid particles, and it can also be used for powder and granular media according to the strength of the sealing surface. It can be applied to the two-way opening and closing and adjustment of ventilation and dust removal pipelines, and is widely used in gas pipelines and water channels in metallurgy, light industry, electric power, and petrochemical systems.

Disadvantages:

① Due to the limitation of the structure of the butterfly valve and the sealing material, it is not suitable to be used in the high temperature and high pressure piping system.
　 ②The sealing performance is worse than that of ball valves and stop valves, so it is used in places where the sealing requirements are not very high.

NO.2

The ball valve is evolved from the plug valve. Its opening and closing part is a sphere, which uses the sphere to rotate 90° around the axis of the valve stem to achieve the purpose of opening and closing. The ball valve is mainly used to cut off, distribute and change the direction of the medium flow in the pipeline.

advantage:

　 ①It has the lowest flow resistance (actually 0);
　　②Because it will not get stuck during work (when there is no lubricant), it can be reliably used in corrosive media and low-boiling liquids;
　　③Under higher pressure It can achieve complete sealing within the range of temperature and temperature;
　　④It can realize rapid opening and closing, which is suitable for the automation system of the test bench. When the valve is 　　opened and closed quickly, there is no impact in operation;
　　⑤The spherical closure can be automatically positioned at the boundary position;
　　⑥The working medium is sealed reliably on both sides;
⑦The sealing surface of the sphere and the valve seat and the medium when fully open and fully closed Isolation, so the medium passing through the valve at high speed will not cause erosion of the sealing surface;
　　⑧Compact structure, light weight, the most reasonable valve structure suitable for medium and low temperature medium system;
　　⑨Symmetrical valve body, especially the overall structure, can be well Withstand the stress from the pipeline;
　　⑩The closing piece can withstand the high pressure difference when it is closed. ⑾The ball valve with fully welded body can be directly buried in the ground, so that the internal parts of the valve are not corroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and natural gas pipelines.

Disadvantages:

　①Because the main seat sealing ring material of the ball valve is polytetrafluoroethylene, it is inert to almost all chemical substances, and has a small friction coefficient, stable performance, not easy to age, wide temperature application range and excellent sealing performance The comprehensive characteristics. However, the physical properties of PTFE, including high expansion coefficient, sensitivity to cold flow and poor thermal conductivity, require the design of valve seat seals to focus on these characteristics. Therefore, when the sealing material becomes hard, the reliability of the seal is impaired. Moreover, PTFE has a low temperature resistance grade and can only be used at less than 180°C. Above this temperature, the sealing material will deteriorate. In the case of long-term use, it will generally only be used at 120°C.

　　② Its adjustment performance is worse than that of the stop valve, especially the pneumatic valve (or electric valve).

NO.3

The shut-off valve is a valve whose closing part (disc) moves along the center line of the valve seat. According to this movement form of the valve disc, the change of the valve seat port is proportional to the valve disc stroke. Since the opening or closing stroke of the valve stem of this type of valve is relatively short, and it has a very reliable cut-off function, and because the change of the valve seat port is in direct proportion to the stroke of the valve disc, it is very suitable for flow adjustment. Therefore, this type of valve is very suitable for cutting off or regulating and throttling.

advantage:

　　①During the opening and closing process, the friction between the valve clack and the sealing surface of the valve body is smaller than that of the gate valve, so it is wear-resistant.
　　②The opening height is generally only 1/4 of the valve seat passage, so it is much smaller than the gate valve;
　　③Usually there is only one sealing surface on the valve body and the valve disc, so the manufacturing process is better and easy to maintain;
　　④Because the packing is general It is polytetrafluoroethylene, so the temperature resistance level is higher.

Disadvantages:

① Since the flow direction of the medium through the valve has changed, the minimum flow resistance of the stop valve is also higher than that of most other types of valves;

②Due to the longer stroke, the opening speed is slower than that of the ball valve.

NO.4

Diaphragm valve refers to a flexible membrane or combined diaphragm installed in the valve body and bonnet, and its closing part is a compression device connected with the diaphragm. The valve seat is weir-shaped.

advantage:

①The control mechanism is separated from the medium passage, which not only ensures the purity of the working medium, but also prevents the possibility of the medium in the pipeline from impacting the working parts of the control mechanism. There is no need to use any form of separate seal at the valve stem, unless it is controlling harmful media Used in this safety facility;

②Because the working medium is only in contact with the diaphragm and the valve body, both of which can use a variety of different materials, the valve can ideally control a variety of working media, especially suitable for media with chemical corrosion or suspended particles.

③Simple structure, only composed of three parts: valve body, diaphragm and valve cover assembly. The valve is easy to quickly disassemble and repair, and the replacement of the diaphragm can be completed on site and in a short time.

Disadvantages:

① Due to the limitation of the diaphragm material, the diaphragm valve is suitable for low pressure and low temperature occasions. Generally not more than 150℃;

②The adjustment performance is relatively poor, and it can only be adjusted in a small range (usually it can be used for flow adjustment when it is closed to 2/3 opening).

NO.5

Check valves are also known as reverse flow valves, check valves, back pressure valves and one-way valves. These valves are automatically opened and closed by the force generated by the flow of the medium in the pipeline, and belong to an automatic valve. The check valve is used in the piping system, and its main function is to prevent the medium from flowing back, prevent the pump and the drive motor from reversing, and to discharge the container medium. Check valves can also be used to supply pipelines for auxiliary systems where the pressure may rise above the system pressure. It can be divided into swing type (rotating by the center of gravity) and lifting type (moving along the axis).

advantage:

　①The working characteristics of the check valve are large load changes and low opening and closing frequency. Once it is put into the closed or open state, the service period is very long, and the movement of moving parts is not required.

Disadvantages:

①Since the check valve is qualitatively determined to be used for fast closing in most practical applications, the medium flows in the opposite direction at the moment when the check valve is closed. As the valve flap is closed, the medium decreases rapidly from the maximum backflow speed. To zero, and the pressure rises rapidly, that is, the phenomenon of "water hammer" that may have a destructive effect on the piping system is generated. Water hammer is a kind of pressure wave in the transient flow in the pressure pipeline. It is the hydraulic shock phenomenon of the pressure rise or fall caused by the change of the fluid velocity in the pressure pipeline. The physical reason is the combined effect of fluid incompressibility, fluid motion inertia and pipeline elasticity. In order to prevent the hidden danger of water hammer in the pipeline, for many years, people have adopted some new structures and new materials in the design of check valves to ensure the applicable performance of the check valve while minimizing the impact of water hammer. Gratifying progress has been made.

Tips：

"Talents are suitable for their own needs, and if they are used appropriately, they will be used, and if they are not used, they will be awkward." Choosing the right valve is the same as employing people in a company. We must know that the valve function itself has no distinction between good and bad. The valve makes good use of its strengths and avoids its shortcomings, uses it properly, and makes full use of its functions.