Advantages and disadvantages of several valves

gate:

Gate valve refers to the valve whose closing member (gate) moves along the vertical direction of the channel axis. It is mainly used to cut off the medium on the pipeline, that is, fully open or fully closed. In general, gate valves cannot be used to regulate flow. It can be applied to low temperature pressure or high temperature and high pressure, and can be used according to different materials of the valve. However, gate valves are generally not used in pipelines that transport mud and other media.

Advantages: 1. Small fluid resistance; 2. Less torque required for opening and closing; 3. It can be used on the ring network pipeline where the medium flows in two directions, which means that the flow direction of the medium is not restricted; 4. When fully opened, the sealing surface is affected by the working medium. The erosion of the valve is smaller than that of the globe valve; ⑤ The body structure is relatively simple, and the manufacturing process is better; ⑥ The structure length is relatively short.

Disadvantages: ①The external dimension and opening height are large, and the space required for installation is also large; ②During the opening and closing process, the sealing surface is relatively rubbed, and the friction loss is large, and even at high temperature, it is easy to cause scratches; ③ Generally, the gate valve has two sealing surfaces, which adds some difficulties to processing, grinding and maintenance; ④ The opening and closing time is long.

Butterfly valve:

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

Advantages: ①Simple structure, small size, light weight, less consumables, suitable for large-diameter valves; ②Quick opening and closing, small flow resistance; ③It can be used for media with suspended solid particles, and can also be used for powder according to the strength of the sealing surface and granular media. It can be used for two-way opening and closing and adjustment of ventilation and dust removal pipelines, and is widely used in gas pipelines and waterways of metallurgy, light industry, electric power, and petrochemical systems.

Disadvantages: ① The flow adjustment range is not large, when the opening reaches 30%, the flow will enter more than 95%. ②Due to the limitation of structure and sealing material of butterfly valve, it should not be used in high temperature and high pressure piping system. The general working temperature is below 300℃ and below PN40. ③The sealing performance is poorer than that of ball valve and globe valve, so it is used in places where sealing requirements are not very high.

Ball valve:

It is evolved from the plug valve. Its opening and closing part is a sphere, and the sphere is rotated 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 flow direction of the medium on the pipeline. The ball valve designed with V-shaped opening also has a good flow adjustment function.

Advantages: ①Low flow resistance (actually 0); ②It can be used in corrosive media and low-boiling liquids because it will not get stuck during operation (when there is no lubricant); ③In higher pressure and temperature range, it can achieve complete sealing; ④ It can realize rapid opening and closing, and the opening and closing time of some structures is only 0.05~0.1s, so as to ensure that it can be used in the automation system of the test bench. When the valve is opened and closed quickly, there is no shock in operation. ⑤The spherical closing part can be automatically positioned at the boundary position; ⑥Double-sided sealing; ⑦When fully open and fully closed, the sealing surface of the ball and valve seat is isolated from the medium, so the medium passing through the valve at high speed will not cause erosion of the sealing surface ;⑧Compact structure and light weight, it can be considered as a reasonable valve structure for low temperature medium system;⑨The valve body is symmetrical, especially the welded valve body structure, which can well withstand the stress from the pipeline; ⑩The closing part can withstand High differential pressure when closed. ⑾The ball valve with fully welded valve body can be directly buried in the ground, so that the valve internals are not corroded, and the long service life can reach 30 years. It is an ideal valve for oil and natural gas pipelines.

Disadvantages: ① Because the main valve seat sealing ring material of the ball valve is PTFE, 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 sealing performance Excellent comprehensive features. But the physical properties of PTFE, including high coefficient of expansion, susceptibility to cold flow, and poor thermal conductivity, require seat seal designs to be built around these properties. Therefore, when the sealing material hardens, the sealing is damaged. Moreover, PTFE has a low temperature resistance grade and can only be used below 180°C. Above this temperature, the sealing material will degrade. In the case of long-term use, it is generally not used at 120 °C. ② Its adjustment performance is worse than that of globe valve, especially pneumatic valve (or electric valve).

  Shut-off valve:

Refers to the valve in which the closing member (disc) moves along the centerline of the valve seat. According to this moving form of the disc, the change of the valve seat port is proportional to the stroke of the disc. Because the valve stem of this type of valve has a relatively short opening or closing stroke, and has a very reliable cut-off function, and because the change of the valve seat port is proportional to the stroke of the valve disc, it is very suitable for flow regulation. Therefore, this type of valve is very adaptable for shut-off or regulation as well as throttling.

Advantages: ①During the opening and closing process, the friction between the valve disc 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 channel, so it is much smaller than the gate valve; ③There is usually only one sealing surface on the valve body and the valve disc, so the manufacturing process is better and it is easy to maintain. ④ Since its filler is generally a mixture of asbestos and graphite, it has a higher temperature resistance level. General steam valves use globe valves.

Disadvantages: ①Due to the change of the flow direction of the medium through the valve, the small flow resistance of the globe 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.

Diaphragm valve:

It means that a flexible membrane or a combined diaphragm is installed in the valve body and valve cover, and its closing part is a compression device connected to the diaphragm. The valve acne can be weir-shaped, or it can be the pipe wall of the straight flow channel.

Advantages: ① The operating 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 impacting the working parts of the operating mechanism. The valve stem does not need to use any form of separate seal, unless the control mechanism is used. It is used as a safety facility in harmful medium; ② Since the working medium is only in contact with the diaphragm and the valve body, both of which can be made of a variety of different materials, so the valve can ideally control a variety of working media, especially suitable for chemical corrosion. or suspended particles. ③ The structure is simple, only composed of three parts: valve body, diaphragm and valve cover assembly. The valve is easy to disassemble and repair quickly, and the replacement of the diaphragm can be done on site and in a short time.

Disadvantages: ① Due to the limitations of the valve body lining process and the diaphragm manufacturing process, it is difficult to manufacture a larger valve body lining and a larger diaphragm, so the diaphragm is not suitable for larger pipe diameters, generally used in DN≤200mm on the following pipeline. ②Due to the limitation of the diaphragm material, the diaphragm valve is suitable for low pressure and low temperature occasions. Generally, it does not exceed 180℃; ③ The adjustment performance is relatively poor, and it is only adjusted in a small range (generally, it can be used for flow adjustment when it is closed to 2/3 of the opening).

The auxiliary system of the system pressure is on the supply pipeline. It can be mainly divided into swing type (rotating according to the center of gravity) and lifting type (moving along the axis).