Advantages and disadvantages of various valves:

1, gate valve: Gate valve refers to the closing part (gate plate) along the vertical direction of the channel axis of the valve, mainly used as a cut off medium in the pipeline, that is, fully open or fully closed use. In general, gate valves cannot be used to regulate flow. It can be applied to low temperature pressure can also be applied to high temperature and high pressure, and can be based on the different materials of the valve. However, gate valves are generally not used in pipelines for conveying mud and other media.

Advantages:

① Low fluid resistance;

② The required torque for opening and closing is small;

(3) It can be used in the loop network where the medium flows in two directions, that is, the flow direction of the medium is not restricted;

④ When fully opened, the erosion of the sealing surface by the working medium is smaller than that of the stop valve;

⑤ The shape structure is relatively simple, and the manufacturing process is better;

⑥ The structure length is relatively short.

Cons:

① The overall size and opening height are large, and the space required for installation is also large;

② In the process of opening and closing, the sealing surface person relative friction, friction loss is large, and even at high temperature easy to cause chafing phenomenon;

(3) General gate valves have two sealing surfaces, which increase some difficulties for processing, grinding and maintenance;

④ Long opening and closing time.

2, butterfly valve: Butterfly valve is a kind of valve that is used to open, close and adjust the fluid channel by rotating the disc type opening and closing parts about 90°.

Advantages:

① Simple structure, small size, light weight, consumables, do not use in large diameter valves;

② Fast 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 applied to the bidirectional opening and closing and adjustment of ventilation and dust removal pipelines, and is widely used in the gas pipelines and waterways of metallurgy, light industry, electric power and petrochemical systems.

Cons:

① The flow adjustment range is not large, when opened up to 30%, the flow will enter more than 95%;

Due to the limitations of the structure and sealing materials of the butterfly valve, it is not suitable for high temperature and high pressure pipeline systems. General operating temperature below 300℃, PN40 below;

③ The sealing performance is poor compared with the ball valve and the globe valve, so it is used in places where the sealing requirements are not very high.

3, ball valve: is evolved from the plug valve, its opening and closing parts are a sphere, the use of the sphere around the axis of the valve stem rotation 90° to achieve the purpose of opening and closing. Ball valve in the pipeline is mainly used to cut off, distribute and change the direction of the flow of the medium, designed into the V-shaped opening ball valve also has a good flow regulation function.

Advantages:

① Has a low flow resistance (actually 0);

(2) Because it will not get stuck during work (when there is no lubricant), it can be reliably applied to corrosive media and low boiling point liquids;

③ In a large pressure and temperature range, can achieve complete sealing;

It can realize fast 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 opening and closing the valve quickly, the operation has no impact;

⑤ Spherical closing parts can be automatically positioned at the boundary position;

⑥ The working medium is sealed reliably on both sides;

7 When fully open and fully closed, the sealing surface of the ball and the 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, light weight, it can be considered to be a reasonable valve structure for low temperature medium systems;

⑨ The valve body is symmetrical, especially the welded valve body structure, can withstand the stress from the pipeline well;

⑩ The closing parts can withstand the high pressure difference when closing. (11) All-welded valve body ball valve, can be directly buried in the ground, so that the valve internals are not corroded, high service life of up to 30 years, is the ideal valve for oil and gas pipelines.

Cons:

Because the main valve seat sealing ring material is polytetrafluoroethylene, it is inert to almost all chemical substances, and has the comprehensive characteristics of small friction coefficient, stable performance, not easy to age, wide range of temperature application and excellent sealing performance. However, the physical properties of teflon, including high coefficient of expansion, sensitivity to cold flow and poor thermal conductivity, require that the seat seal be designed around these characteristics. Therefore, when the sealing material hardens, the reliability of the seal is damaged. Moreover, the temperature resistance of PTFE is low 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.

Its adjustment performance is worse than that of the globe valve, especially the pneumatic valve (or electric valve).

4, globe valve: refers to the closing part (valve disc) along the center line of the valve seat. According to this form of movement of the valve disc, the change of the valve seat port is proportional to the stroke of the valve disc. Because the stem opening or closing stroke of this type of valve is relatively short, and has a very reliable cutting function, and because the change of the valve seat port is directly proportional to the stroke of the valve disc, it is very suitable for the adjustment of the flow rate. Therefore, this type of valve is very suitable for switching off or regulating as well as throttling.

Advantages:

① In the opening and closing process, because the friction between the disc and the valve body sealing surface is smaller than the gate valve, it is wear-resistant.

② The opening height is generally only 1/4 of the valve seat channel, so it is much smaller than the gate valve;

(3) Usually there is only one sealing surface on the valve body and valve 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 grade. General steam valves use stop valves.

Cons:

Because the flow direction of the medium through the valve has changed, the small flow resistance of the stop valve is also higher than that of most other types of valves;

② Due to the long stroke, the opening speed is slower than the ball valve.

5, plug valve: refers to the closing part into a plunger shaped rotary valve, through 90 degrees of rotation so that the valve plug on the port and the valve body on the port is connected or separated, to achieve the opening or closing of a valve. The valve plug can be cylindrical or conical in shape. 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.

6, safety valve: refers to the pressure container, equipment or pipeline, as an overpressure protection device. When the pressure rise in the equipment, container or pipeline exceeds the allowable value, the valve automatically opens, and then the full discharge to prevent the equipment, container or pipeline and pressure from continuing to rise; When the pressure is reduced to the specified value, the valve should be automatically closed in time to protect the safe operation of the equipment, container or pipeline.

7, steam trap: in the transmission of steam, compressed air and other media, there will be some condensate formation, in order to ensure the efficiency and safe operation of the device, it should be timely discharge of these useless and harmful media to ensure the consumption and use of the device. It has the following functions: ① can quickly eliminate the condensate produced; ② Prevent steam leakage; ③ Remove air and other non-condensable gases.

8, pressure reducing valve: by adjusting, the inlet pressure is reduced to a certain required outlet pressure, and rely on the energy of the medium itself, so that the outlet pressure is automatically stable valve.

9, check valve: also known as counter-flow 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 belong to an automatic valve. The check valve is used in the piping system, and its main function is to prevent the backflow of the medium, prevent the reversal of the pump and the drive motor, and the drainage of the container media. Check valves can also be used to supply pipes in which the pressure may rise to exceed the system pressure to supply auxiliary systems, and can be mainly classified as swing (rotating against the center of gravity) and lift (moving along the axis).