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Advantages and Disadvantages of Several Valves

Gate valve:
         Gate valve refers to the valve whose closing part (gate) moves vertically along the axis of the passage. It is mainly used as cutting medium in the pipeline, i.e. fully open or fully closed. Generally, gate valve can not be used as flow regulation. It can be applied to low temperature pressure can also be applied to high temperature and high pressure, and according to the different material of the valve. But gate valves are generally not used in pipelines to transport mud and other media.
 
         Advantages: 1) small fluid resistance; 2) small opening and closing moment; 3) can be used in the annular network pipeline where the medium flows in both directions, that is, the flow direction of the medium is not limited; 4) when fully opened, the erosion of the sealing surface by the working medium is smaller than that of the globe valve; the structure of the body is relatively simple and the manufacturing process is better; _the length of the structure is relatively short.
 
         Disadvantages: 1) large size and opening height, the space required for installation is also large; 2) in the opening and closing process, the sealing surface is relatively frictional, friction is large, and even easy to cause abrasion phenomenon at high temperature; 3) general gate valves have two sealing surfaces, which add some difficulties to processing, grinding and maintenance; 4) long opening and closing time.
 
Butterfly valve:
 
         Butterfly valve is a kind of valve that opens, closes and regulates fluid passage by reciprocating about 90 degrees of disc-type opening and closing parts.
         Advantages: 1) simple structure, small size, light weight, low consumption of materials, suitable for large caliber valves; 2) quick opening and closing, low flow resistance; 3) can be used for medium 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 two-way opening and closing of ventilation and dust removal pipelines, and is widely used in gas pipelines and waterways of metallurgical, light industry, electric power and petrochemical systems.
 
         Disadvantage: 1. Flow regulation range is not large, when the opening is up to 30%, the flow will be more than 95%. Because of the restriction of butterfly valve structure and sealing material, it is not suitable for high temperature and high pressure pipeline system. The general working temperature is below 300 C and PN40. (3) Sealing performance is worse than ball valves and globe valves, so it is used in places where sealing requirements are not very high.
 
Globe valve:
 
         It is evolved from the cock valve. Its opening and closing part is a sphere, which rotates 90 degrees around the axis of the valve stem to achieve the purpose of opening and closing. Ball valve is mainly used to cut off, distribute and change the direction of medium flow in pipeline. The ball valve with V-shaped opening also has good flow regulation function.
 
         Advantages: 1. Low flow resistance (actual 0); 2. It can be used in corrosive media and low boiling point liquids because it can not be stuck in operation (without lubricant); 3. Full sealing can be achieved in a larger range of pressure and temperature; 4. Quick opening and closing can be achieved, 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 bed. 。 When the valve is opened and closed quickly, there is no impact in operation. Spherical closure can be positioned automatically at the boundary position; Double-sided seal; When fully open and fully closed, the sealing surface of the sphere and seat is isolated from the medium, so the medium passing through the valve at high speed will not cause the erosion of the sealing surface; compact structure and light weight, it can be considered as a reasonable valve structure for cryogenic medium system; The valve body is symmetrical, especially for welding the valve body. The structure can well withstand the stress from the pipeline; _The closing parts can withstand the high pressure difference when closing. _Fully welded ball valve body can be buried directly underground, so that the inner parts of the valve can not be eroded, and its long service life can reach 30 years. It is an ideal valve for oil and natural gas pipelines.
 
         Disadvantages: 1. Because the main seating ring material of ball valve is PTFE, it is inert to almost all chemical substances, and has the comprehensive characteristics of small friction coefficient, stable performance, not easy to aging, wide temperature application range and excellent sealing performance. However, the physical properties of PTFE, including high expansion coefficient, sensitivity to cold flow and poor heat conductivity, require the design of seat seals around these characteristics. Therefore, when the sealing material hardens, the sealing feasibility is destroyed. Moreover, PTFE has a lower temperature resistance and can only be used at less than 180 C. Over this temperature, the sealing material will age. Considering the long-term use, it is usually not used at 120 C. (2) Its regulating performance is worse than that of globe valves, especially pneumatic valves (or electric valves).
 
Globe valve:
 
         Valve refers to a valve whose closure (disc) moves along the center line of the seat.  According to this movement of the disc, the change of the seat opening is proportional to the disc stroke. Because the stem opening or closing stroke of this kind of valve is relatively short, and has a very * cut-off function, and because the change of the seat opening is proportional to the disc travel, it is very suitable for flow regulation. Therefore, this type of valve is very flexible for cutting or regulating and throttling.
 
         Advantages: 1. In the process of opening and closing, the friction between the disc and the sealing surface of the valve body is smaller than that of the gate valve, so it is wearable. The opening height is generally only 1/4 of the seat passage, so it is much smaller than the gate valve. 3. There is usually only one sealing surface on the valve body and disc, so the manufacturing process is better and easy to maintain. (4) Because its filler is generally a mixture of asbestos and graphite, it has a higher temperature resistance. Generally steam valves are cut-off valves.
 
         Disadvantages: 1. Because the flow direction of medium through the valve has changed, the small flow resistance of the globe valve is also higher than that of most other valves.