Valve: Valve is shut down part (disc) valve moves vertically along the channel axis in the pipeline as a cut off media with, that is fully on or off. In general, the gate valve can not adjust the flow use. It can be applied to low-temperature pressure can be applied to high temperature and pressure, and according to the different materials of the valve. But the gate valve is generally not used in pipeline transportation of mud, and other media.
Advantages: (1) fluid resistance is small; ② The Kai, closed the required torque is smaller; (3) you can use in the media ring network on the road to the two direction flow, which means that the flow of media without restriction; ④ The fully open, the sealing surface by the erosion of the working medium than globe valves; ⑤ The body structure is relatively simple, good manufacturing processes; ⑥ The structure length is relatively short.
Disadvantages: (1) Dimensions and opening height of the larger space required to install; 2 in the opening and closing process, the sealing surface relative friction, wear large easily lead to abrasions, and even at high temperatures [J]; general gate valve has two sealing surface, to processing, polishing and maintenance of an increase of some difficulty; ④ The opening and closing a long time.

Butterfly: The butterfly valve disc opening and closing pieces back and forth rotation about 90 ° to open, close and adjust a valve of the fluid channel.
Advantages: (1) simple structure, small size, light weight, supplies province, particularly for large diameter valves open and close quickly; 2, small flow resistance coefficient; (3) can be used with suspended solid particles of the medium, based on the strength of the sealing surface of the be used in powder and granular media. Applicable to two-way opening and closing and adjustment of ventilation and dust removal piping is widely used in metallurgy, light industry, electric power, petrochemical, gas pipelines and waterways.
Disadvantages: (1) flow adjustment range is small, when open up to 30%, the flow will be into more than 95%. ② Due to the restrictions of the structure of the butterfly valve and seal materials should not be used for high temperature, high pressure piping systems. General operating temperature below 300 ℃, PN40 (6 to 40). The ③ sealing performance relative to the ball valve, globe valve is poor, it is used to place seal is not very high.

Ball: by the stopcock evolved its opening and closing parts of a sphere, the sphere around the stem axis rotated 90 ° to achieve the purpose of opening and closing. The ball valve on the pipe is mainly used to cut distribution and change the flow direction of medium designed V-shaped openings of the ball valve also has a good flow regulation.
Advantages: (1) with the lowest flow resistance (real 0); ② not stuck at work (in the absence of lubricant), it can be reliably used in the corrosive medium and low boiling point liquid; ③ in the larger pressure and temperature range, can be completely sealed; ④ fast opening and closing, opening and closing time of some of the structure is only 0.05 ~ 0.1s, can be used to ensure that the test bed automation system. Rapid opening and closing valves, the operation no impact. ⑤ spherical shut down in the border position automatic positioning; ⑥ working medium is reliable sealing on both sides; ⑦ in the fully open and fully closed, the ball and seat sealing surface and the dielectric isolation, speed through the valve media will cause erosion of the sealing surface; the ⑧ compact, light weight, that it is the most reasonable of the valve structure for low-temperature dielectric system; ⑨ body symmetry, especially in the welded body structure, can withstand from pipe stress; ⑩ off parts can withstand the pressure differential. Full welded ball valve in ⑾ can be buried underground, so that the valve inner parts from erosion, the maximum service life of up to 30 years, the oil, natural gas pipeline valve ideal.
Disadvantages: (1) ball valve main seat ring material is PTFE, it is almost all chemicals is inert and has a coefficient of friction is small, stable performance, easy to aging, wide temperature ranges and Sealing the excellent performance characteristics. The physical properties of PTFE, including the high expansion coefficient, the sensitivity of the cold and poor thermal conductivity, required seating design must focus on these characteristics. So, when the sealing material hardens, the reliability of sealing damaged. Moreover, the PTFE low temperature levels, only in the case of less than 180 ℃. Exceed this temperature, the sealing material is aging. Consider the long-term use, usually only at 120 ° C is not used. ② its regulation performance relative to the valve to be worse, especially pneumatic valve (electric valve).

Valve: refers to the closure of parts (disc) moving the valve along the valve seat centerline. According to this mobile form of the valve, the seat through the mouth of the change is directly proportional relationship with the valve stroke. The type of the valve stem to open or close the trip is relatively short, but very reliable cut, due to changes in the valve seat openings and the valve stroke is proportional to the very suitable for flow regulation. Therefore, this type of valve is suitable as a cut or adjust the throttle with.
Advantages: (1) in the process of opening and closing, due to the friction between the valve and valve sealing surface is smaller than the gate, and therefore wear. ② Open height is generally only 1/4 of the seat channel, and therefore much smaller than the gate; the ③ usually in the valve body and disc only one sealing surface, and thus manufacturing processes, ease of maintenance. ④ Because of its filler is generally a mixture of asbestos and graphite, so a higher temperature rating. General steam valve with shutoff valve.
Disadvantages: (1) due to a change in the direction of flow of medium through the valve, cut-off valve minimum flow resistance higher than most other types of valves; ② Because the trip is longer, the opening speed is slower than the ball valve.

Diaphragm: refers to a flexible membrane or a combination of diaphragm inside the body and bonnet, shut down parts of the diaphragm is connected to a compression device. Valve acne weir shape, can also be a direct flow path of the wall.
Advantages: (1) manipulation of the institutions and the media path are separated not only to ensure the purity of the working media, but also to prevent the possibility of the impact of media control mechanism in the pipeline working parts, the stem Department does not require any form of individually sealed, except in the control harmful media for this safety facilities; ② working media only contact with the diaphragm and the valve body, both of which can be used a variety of different materials, so the valve can be ideal to control a variety of working medium, is particularly suitable with chemical corrosion or suspended particles of the medium. ③ simple structure, the assembly of three components constitute only by the valve body, diaphragm, and valve cover. The valve is easy to fast disassembly and repair, and replacement of the diaphragm can be completed at the scene and within a short time.
Disadvantages: (1) due to body lining and diaphragm technology manufacturing processes and limitations, the larger body lining and large diaphragm manufacturing process is difficult, so the diaphragm is not suitable for a large diameter, generally used in the DN ≤ 200mm following the pipeline. ② Due to the limitations of the diaphragm material, diaphragm valves for low pressure and high temperature situations. Generally not more than 180 ° C; ③ regulation performance is relatively poor, only a small range of adjustment (usually shut down to 2/3 opening, can be used for flow regulation).

Safety valve: refers to the pressure vessel, equipment or pipeline, as overpressure protection device. Equipment, container or piping within the pressure exceeds the allowable value, the valve automatically open, then the whole amount of emissions in order to prevent the equipment, container or piping, and pressure continues to rise; when the pressure is reduced to the specified value, the valve should automatically be closed, to protect the safe operation of equipment, container or piping.

Steam Traps: In conveying steam, compressed air and other media, there will be some condensate formation, in order to ensure the efficient and safe operation of the device, it should be timely discharge of these useless and harmful media, to ensure that the consumption and use of the device .
It has the following functions: ① quickly excluded the condensate; ② to prevent steam leakage; (3) to exclude air and other non-condensable gas.

Pressure reducing valve: through the adjustment will reduce the inlet pressure to a desired outlet pressure, energy and rely on the media itself, so that the outlet pressure to automatically maintain a stable valve.

Check valve: also known as reflux valve, check valve, back pressure valve and check valve. The valve is automatically turned on and off by the force generated by the flow of the medium itself rely on piping, is an automatic valve. The check valves used in piping systems, its main role is to prevent the media back to prevent the discharge of the pump and drive motor reversal, as well as container media. The check valve can also be used to which the pressure may rise to the auxiliary system supplies more than the system pressure pipeline. Can be divided into the swing (rotation) according to the center of gravity and lift (along the axis of movement).

The definition of the valve flow coefficient:

1, C: in the valve is fully open, the temperature of 5 ~ 40 ° C water, across the valve differential pressure 1kgf/cm2 per hour, the volume flowing through the valve (m3). C is the universal symbol of the flow coefficient, our long-term use in the past.
2, Kv: valve is fully open, the temperature of 5 ~ 40 ° C water, across the valve differential pressure 100KPa per hour flowing through valve volume (m3). Kv = 1.01C, China is recommended.
3, Cv: the valve is fully open, the temperature to 15 ° C (60 degrees Fahrenheit) water, across the valve differential pressure 1lb/in2 per hour flowing through the valve when the volume (m3). Cv = 1.167C

Valve flow coefficient and cavitation coefficient introduced

The valve flow coefficient and cavitation coefficient are two important parameters, generally in the advanced industrial countries in the production of valve data can provide, even in the sample print. Produced in our country valve is basically no information in this regard, because of the need to do the experiment in order to obtain this information, which is one of the important manifestations of our country and the world advanced level in the valve gap.

keywords: Channel, gate, opening and closing valves, suspended solids,