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Various valve working principles and valve advantages and disadvantages

Advantages and disadvantages of various valves:
1. Gate valve: A gate valve is a valve that moves the closing member (gate) in the vertical direction of the channel axis. It is mainly used as a cutting medium in the pipeline, that is, fully open or fully closed. In general, gate valves are not available for regulated flow. It can be applied to low temperature pressure or high temperature and high pressure, and can be made according to different materials of the valve. However, gate valves are generally not used in pipelines for conveying media such as mud.
advantage:
1 fluid resistance is small;
2 The required torque for opening and closing is small;
3 can be used on the ring flow of the medium flowing in both directions, that is to say, the flow direction of the medium is not limited;
4 When fully open, the sealing surface is less affected by the working medium than the shut-off valve;
The shape of the body is relatively simple and the manufacturing process is better;
6 structure length is relatively short.
Disadvantages:
1 The external dimensions and opening height are large, and the required installation space is also large;
2 During the opening and closing process, the sealing surface is relatively frictional, the friction is large, and even the high temperature is likely to cause scratches;
3The general gate valve has two sealing faces, which adds some difficulties to processing, grinding and maintenance;
4 The opening and closing time is long.
2. Butterfly valve: A butterfly valve is a valve that opens and closes and adjusts the fluid passage by reciprocating about 90° with a disc type opening and closing member.
advantage:
1The structure is simple, the volume is small, the weight is light, the consumables are saved, and it is not used in large-diameter valves;
2 rapid opening and closing, small flow resistance;
3 can be used for media with suspended solid particles, and can also be used for powdery and granular media depending on 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. It 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 is up to 30%, the flow rate will be more than 95%;
2 Due to the structure of the butterfly valve and the limitation of the sealing material, it is not suitable for use in high temperature and high pressure piping systems. The general working temperature is below 300 ° C, below PN40;
3 Sealing performance is relatively poor compared to ball valves and globe valves, so it is not used for sealing requirements.
3, the ball valve: is evolved from the plug valve, its opening and closing member is a sphere, using the ball 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, distribute and change the flow direction of the medium on the pipeline. The ball valve designed as a V-shaped opening also has a good flow regulation function.
advantage:
1 has the lowest flow resistance (actually 0);
2 It can be reliably applied to corrosive media and low boiling liquids because it will not get stuck during work (in the absence of lubricant);
3 can achieve complete sealing within a large pressure and temperature range;
4 can achieve fast opening and closing, 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 quickly opened and closed, the operation has no impact;
5 spherical closures can be automatically positioned at the boundary position;
6 working medium is sealed reliably on both sides;
7 When fully open and fully closed, the sealing surface of the ball and the valve seat is isolated from the medium, so the medium passing through the valve at high speed does not cause erosion of the sealing surface;
8 compact and lightweight, it can be considered as the most reasonable valve structure for low temperature media systems;
9 valve body symmetry, especially the welded valve body structure, can well withstand the stress from the pipeline;
10 closing parts can withstand the high pressure difference when closing. (11) The ball valve of the fully welded valve body can be buried directly in the ground, so that the valve internals 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:
1Because the most important seat seal material of the ball valve is PTFE, it is inert to almost all chemicals, and has a small friction coefficient, stable performance, not easy to age, wide temperature range and excellent sealing performance. Comprehensive features. However, the physical properties of Teflon, including higher coefficient of expansion, sensitivity to cold flow, and poor thermal conductivity, require that the design of the seat seal must be centered around these characteristics. Therefore, when the sealing material is hardened, the reliability of the sealing is broken. Moreover, PTFE has a low temperature resistance and can only be used at less than 180 °C. Above this temperature, the sealing material will age. In the case of long-term use, it is generally not used at 120 °C.
2 Its adjustment performance is worse than the shut-off valve, especially the pneumatic valve (or electric valve).
4. Globe valve: refers to the valve that moves the closing member (valve) along the center line of the valve seat. Depending on the form of movement of the flap, the change in the seat opening is proportional to the flap travel. Due to the relatively short opening or closing stroke of the valve stem of this type of valve, and the very reliable cutting function, and because the change of the valve seat opening is proportional to the stroke of the valve flap, it is very suitable for the adjustment of the flow rate. Therefore, this type of valve is very cooperative for cutting or regulating and throttling.
advantage:
1 During the opening and closing process, the friction between the valve flap and the sealing surface of the valve body is smaller than that of the gate valve, so it is wear-resistant.
2 The opening height is generally only 1/4 of the valve seat passage, so it is much smaller than the gate valve;
3 Usually there is only one sealing surface on the valve body and the valve flap, so the manufacturing process is better and easy to repair;
4 Because the filler is generally a mixture of asbestos and graphite, the temperature resistance level is higher. Generally, steam valves use a shut-off valve.
Disadvantages:
1 Since the flow direction of the medium through the valve changes, the minimum flow resistance of the shut-off valve is also higher than most other types of valves;
2 Due to the long stroke, the opening speed is slower than the ball valve.
5. Plug valve: It refers to a rotary valve whose closing member is a plunger shape. The valve opening on the valve plug is connected or separated from the passage opening on the valve body by 90° rotation to realize a valve that is opened or closed. The shape of the valve plug can be cylindrical or conical. The principle is basically similar to that of the ball valve. The ball valve is developed on the basis of the plug valve. It is mainly used for oil field exploitation and also used in petrochemical industry.
6. Safety valve: refers to the overpressure protection device on the pressurized container, equipment or pipeline. When the pressure in the equipment, vessel or pipeline rises above the allowable value, the valve is automatically opened and then discharged in full to prevent the equipment, vessel or piping and pressure from continuing to rise; when the pressure drops to the specified value, the valve shall automatically Closed in time to protect the safe operation of equipment, containers or pipelines.
7. Steam trap: In the medium of steam, compressed air, etc., some condensed water will be formed. In order to ensure the working efficiency and safe operation of the device, these useless and harmful media should be discharged in time to ensure the consumption of the device and use. It has the following effects: 1 can quickly eliminate the condensed water produced; 2 prevent steam leakage; 3 exclude air and other non-condensable gases.
8. Pressure reducing valve: It is a valve that adjusts the inlet pressure to a certain required outlet pressure and relies on the energy of the medium itself to make the outlet pressure automatically maintain stable.
9, check valve: also known as counterflow valve, check valve, back pressure valve and check valve. These valves are automatically opened and closed by the force generated by the flow of the medium itself in the pipeline, and are an automatic valve. Check valves are used in piping systems and their primary function is to prevent backflow of media, prevent pump and drive motor reversal, and venting of container media. The check valve can also be used to supply a line in which the pressure may rise to an auxiliary system that exceeds the system pressure. It can be divided into a swing type (by gravity center) and a lift type (moving along the axis).

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