4, ball valve
Ball valve is evolved from the plug valve, its opening and closing is a ball, using the ball around the axis of the stem rotation 90° 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 into a V-shaped opening also has a good flow regulation function.
Advantages:
Has the lowest flow resistance;
(2)can be used reliably in corrosive media and low boiling point liquids because it will not get stuck when working (in the absence of lubricants);
(3) In the larger pressure and temperature range, can achieve complete sealing;
(4) Can realize fast opening and closing, some structure opening and closing time is only 0.05~0.1s, in order to ensure that it can be used in the test bench automation system.When the valve is opened and closed quickly, there is no impact in operation;
(5) The spherical closing member can be automatically positioned on the boundary position;
â‘¥ The working medium is sealed reliably on both sides;
⑦When fully open and fully closed, the sealing surfaces of the ball and the valve seat are isolated from the medium, so the medium passing through the valve at high speed will not cause corrosion of the sealing surface;
⑧Compact structure and light weight, it can be considered as the most reasonable valve structure for low temperature medium system;
⑨ The valve body is symmetrical, especially the welded valve body structure, can well bear the stress from the pipeline;
⑩The closing piece can withstand the high pressure difference during closing. ⑾The ball valve with fully welded body can be buried directly in the ground, so that the internal parts of the valve are not eroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and natural gas pipelines.
Disadvantages:
â‘  Because the main seat seal material of Cast Steel Ball Valve is PTFE, it is inert to almost all chemical substances, and has a small friction coefficient, stable performance, not easy to age, Comprehensive characteristics of wide temperature range and excellent sealing performance. However, the physical characteristics of PTFE, including a high expansion coefficient, sensitivity to cold flow and poor thermal conductivity, require that the design of the valve seat seal must be carried out around these characteristics. Therefore, when the sealing material becomes hard, the reliability of the seal is destroyed. Moreover, PTFE has a low temperature resistance level and can only be used at less than 180°C. Above this temperature, the sealing material will age. When considering long-term use, it is generally not used at 120 ℃.
â‘¡ Its regulating performance is worse than that of cut-off valve, especially pneumatic valve (or electric valve).
5. Plug Valve
Plug valve: refers to a rotary valve with a plunger-shaped closing member. The passage port on the valve plug is communicated or separated with the passage port on the valve body by 90° rotation to realize opening or closing. The shape of the valve plug can be cylindrical or conical. The principle is basically similar to the ball valve. The ball valve is developed on the basis of the plug valve, which is mainly used for oilfield exploitation, but also for petrochemical industry.
advantage:
1. It is used for frequent operation, opening and closing quickly and easily.
2. The fluid resistance is small.
3. Simple, relatively small size, light weight, easy to maintain.
4. Good sealing performance.
5. Restricted by the installation direction, the flow direction of the media can be arbitrary.
6. No vibration and low noise.
Disadvantages:
1. The cover is too large, which causes too much torque and is not flexible enough.
2. Due to the influence of body weight, the caliber is limited.
3. In actual use, if a large-sized valve is used, a reverse plug structure must be used, which easily affects the sealing effect.
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