The advantages and disadvantages of several types of valves


Gate valve.

Gate valve is the closing member (gate) along the vertical direction of the axis of the channel to move _ the valve, in the pipeline mainly as a cut-off medium with, that is, fully open or fully closed use. In general, the gate valve may not be used as a regulating flow. It can be applied to low temperature pressure can also be applied to high temperature and high pressure, and can be different materials according to the valve. But the gate valve is generally not used in the pipeline for transporting slurry and other media.

Advantages: ① fluid resistance is small; ② opening and closing torque required is small; ③ can be used in the media flow in both directions of the ring network pipeline, that is, the flow direction of the medium is not restricted; ④ fully open, the sealing surface by the working medium erosion than the globe valve is small; ⑤ shape structure is relatively simple, manufacturing process is better; ⑥ structure length is relatively short.

Disadvantages: ① shape size and opening height is larger, the space required for installation is also larger; ② in the process of opening and closing, the sealing surface people relative friction, friction loss is larger, even to be at high temperatures easily caused by abrasion phenomenon; ③ general gate valve have two sealing surface, to processing, grinding and maintenance increased some difficulties; ④ opening and closing time is long.


Butterfly valve.

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

Advantages: ① simple structure, small volume, light weight, consumables saving, suitable for large diameter valves; ② rapid opening and closing, small flow resistance; ③ can be used for media with suspended solid particles, according to the strength of the sealing surface can also be used for powder and granular media. It can be used for bi-directional opening and closing and adjustment of ventilation and dust removal pipeline, widely used in metallurgy, light industry, electric power, petrochemical system of gas pipelines and waterways, etc.

Disadvantages: ① flow adjustment range is not large, when opened up to 30%, the flow will enter more than 95%. ②Because of the structure of the butterfly valve and sealing material restrictions, should not be used in high temperature, high pressure pipeline system. The general working temperature is below 300℃ and below PN40. ③Sealing performance is poor compared to ball valve and globe valve, so it is used in places where sealing requirements are not very high.


Ball valve.

Is evolved from the plug valve, its opening and closing member is a sphere, the use of the sphere around the axis of the stem rotate 90 ° to achieve the purpose of opening and closing. Ball valve in the pipeline is mainly used to cut off, distribution and change the direction of media flow, designed to V-shaped opening of the ball valve also has a good flow regulation function.

Advantages: ① has a low flow resistance (actually 0); ② can be applied to corrosive media and low boiling point liquids because it does not jam during operation (in the absence of lubricant); ③ can achieve complete _ complete sealing in a wide range of pressure and temperature; ④ can achieve rapid opening and closing, with opening and closing times of only 0.05~0.1s for some structures to ensure that it can be used in the automated system of the test bench. When opening and closing the valve quickly, the operation is shock-free. ⑤The spherical closing member can be automatically positioned at the boundary position; ⑥Sealing on both sides; ⑦In full opening and full closing, the sealing surface of the ball and 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 a reasonable valve structure for low temperature medium system; ⑨The valve body is symmetrical, especially the welded body structure, which can well withstand the stress from the pipeline Stress; ⑩Closing member can withstand the high pressure difference when closed. (11) all-welded body of the ball valve, can be buried directly underground, so that the valve internals are not leached, high service life of up to 30 years, is the ideal valve for oil and gas pipelines.


Disadvantages: ① Because the main seat seal material of the ball valve is PTFE, it is inert to almost all chemical substances, and has a small coefficient of friction, stable performance, not easy to age, a wide range of temperature and excellent sealing performance of the comprehensive characteristics. However, the physical properties of PTFE, including high coefficient of expansion, sensitivity to cold flow and poor thermal conductivity, require the design of the valve seat seal around these characteristics. Therefore, when the seal material hardens, the seal's are damaged. Moreover, PTFE has a low temperature resistance rating and can only be used at less than 180°C. Above this temperature, the sealing material will deteriorate. And consider the long-term use of the case, generally only at 120 ℃ will not be used. ②It has poorer adjustment performance compared to globe valves, especially pneumatic valves (or electric valves).


Globe valve.

It is the valve that the closing member (valve flap) moves _ along the center line of the valve seat. According to this form of valve valve movement, the change of the valve seat opening is proportional to the valve stroke. Because of the relatively short opening or closing stroke of the stem of this type of valve, and has a very * cut-off function, and because the change of the seat opening is proportional to the stroke of the valve, it is very suitable for the regulation of the flow. Therefore, this type of valve is very suitable for cutting off or regulating as well as throttling with.

Advantages: ① In the process of opening and closing, because the friction between the valve flap and the valve body sealing surface is smaller than the gate valve, and therefore 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 valve flap, so the manufacturing process is better and easier to maintain. ④Since its packing is generally a mixture of asbestos and graphite, it has a higher temperature resistance rating. General steam valves are used for globe valves.

Disadvantages: ① Because the direction of media flow through the valve has changed, the small flow resistance of the globe valve is also higher than most other types of valves; ② Because of the longer stroke, the opening speed is slower than that of the ball valve.


Diaphragm valve.

It is a compression device equipped with a flexible membrane or combination diaphragm inside the valve body and cover, and its closing member is connected to the diaphragm. Valve acne can be weir-shaped, but also straight through the wall of the flow channel.

Advantages: ① manipulation mechanism and the media pathway is separated, not only to ensure the purity of the working medium, but also to prevent the possibility of pipeline media impact manipulation mechanism working parts, the stem does not need to use any form of individual sealing, except in the control of harmful media for the use of safety facilities; ② as the working medium in contact with only the diaphragm and the valve body, both of which can be used in a variety of different materials, so the valve can ideal control of a variety of working media, especially suitable for the media with chemical corrosion or suspended particles. ③Simple structure, consisting of only three parts: valve body, diaphragm and bonnet assembly. The valve is easy to quickly disassemble and repair, replacement of the diaphragm can be completed in the field and in a short time.

Disadvantages: ① due to the valve body lining process and diaphragm manufacturing process and restrictions, larger valve body lining and larger diaphragm manufacturing process are difficult, so the diaphragm should not be used for larger pipe diameter, generally applied in DN ≤ 200mm below the pipeline. ② Due to the limitations of the diaphragm material, diaphragm valves are suitable for low pressure and temperature is not high. Generally not more than 180 ℃; ③ adjustment performance is relatively poor, only in a small range of adjustment (generally in the closed to 2 / 3 open, can be used for flow regulation).

System pressure of the auxiliary _ help system to provide recharge of the pipeline. Mainly can be divided into rotary (rotating according to the center of gravity) and lifting type (moving _ along the axis).