Comparison of the advantages and disadvantages of various valves

Gate valve: Gate valve is the closing piece (gate) along the vertical axis of the channel to move the valve, mainly in the pipeline as a cut-off media, that is, fully open or closed. In general, the gate valve can not be used as regulating flow. It can be applied to low temperature pressure can also be applied to high temperature and pressure, and according to the valve of different materials. However, the gate valve is generally not used for transporting medium such as mud in the pipeline. Advantages: ① small fluid resistance; ② Kai, closing the required torque is small; ③ can be used in the medium flow in both directions of the ring network pipeline, which means that the flow of media is not restricted; ④ fully open, the sealing surface by the work Medium erosion than the globe valve is small; ⑤ body structure is relatively simple, manufacturing technology is better; ⑥ shorter length of the structure. Disadvantages: ① large size and opening height, the installation space is also larger; ② in the opening and closing process, the sealing surface of the relative friction, wear larger, even at high temperatures tend to cause scratches; ③ Gate valve has two general sealing surface, giving processing, grinding and maintenance increased some difficulties; ④ open and close a long time. Butterfly valve: Butterfly valve is a circular opening and closing pieces about 90 ° rotation back and forth to open, close and regulate the fluid channel of a valve. Advantages: ① simple structure, small size, light weight, consumables province, do not use for large-caliber valves; ② quick opening and closing, flow resistance is small; ③ can be used for medium with suspended solids, according to the strength of the sealing surface can also be used Powdered and granular media. It can be used for bidirectional opening and closing and adjustment of ventilation and dust removal pipeline. It is widely used in gas pipeline and waterway of metallurgy, light industry, electricity and petrochemical industry. Disadvantages: ① flow adjustment range is not large, when the open up to 30%, the flow rate reached nearly 95%. ② Due to the structure of the butterfly valve and sealing material restrictions, should not be used for high temperature, high pressure piping system. General working temperature below 300 ℃, pn40 below. ③ sealing performance relative to the ball valve, globe valve is poor, it is used for sealing the place is not very high. Ball valve: is evolved by the plug valve, and its opening and closing pieces is a sphere, the use of the ball around the axis of the stem rotated 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 medium flow, designed as a v-shaped opening of the valve also has a good flow regulating function. Advantages: ① has the lowest flow resistance (in fact, 0); ② due to work will not get stuck (in the absence of lubricant), it can be reliably used in corrosive media and low boiling point liquid; ③ larger Of the pressure and temperature range, can achieve a complete seal; ④ can achieve fast opening and closing, opening and closing time of some structures only 0.05 ~ 0.1s, to ensure that the test bed can be used in automation systems. Quick opening and closing the valve, the operation without impact. ⑤ spherical closure can be automatically positioned in the border position; ⑥ working medium sealed on both sides of reliable; ⑦ in the fully open and fully closed, the sealing surface of the ball and the valve seat and media isolation, so the high-speed valve through the media will not Resulting in erosion of the sealing surface; ⑧ compact structure, light weight, it can be considered for low temperature medium system is the most reasonable valve structure; ⑨ valve body symmetry, especially welded body structure, can well withstand the stress from the pipe ; ⑩ closing pieces can withstand the high pressure drop off. ⑾ fully welded ball valve body can be buried directly in the ground, so that the valve parts from erosion, the highest life of up to 30 years, is the ideal oil and gas pipelines valves. Disadvantages: ① because the ball valve seat ring is the most important material PTFE, which is almost all of the chemical substances are inert, and has a small friction coefficient, stable performance, easy to aging, wide temperature range and sealing Excellent performance of the comprehensive features. However, the physical properties of polytetrafluoroethylene, including its high coefficient of expansion, sensitivity to cold flow and poor thermal conductivity, require that seat seal design be centered around these characteristics. Therefore, when the sealing material is hardened, the reliability of the sealing is destroyed. Moreover, the low temperature grade of PTFE, can only be used in less than 180 ℃. Above this temperature, the sealing material will age. Considered long-term use of the case, generally only used at 120 ℃. ② its regulating performance relative to the cut-off valve to be worse, especially pneumatic valve (or electric valve). Shut-off valve: refers to the closing piece (valve flap) along the valve seat center line of the valve. Depending on the type of movement of the valve disc, the change in valve seat opening is in direct proportion to the valve disc stroke. Due to the valve stem of this type of valve opening or closing stroke is relatively short, but also has a very reliable cut-off function, but also because the valve seat opening changes in proportion with the valve stroke is proportional to the flow rate is very suitable for regulation. Therefore, this type of valve is very moving together as cut off or adjust and throttle. Advantages: ① in the process of opening and closing, due to the friction between valve disc and valve sealing surface is smaller than the gate valve, which wear. ② opening height is generally only 1/4 of the valve seat passage, so much smaller than the gate valve; ③ usually there is only one sealing surface on the valve body and valve disc, so manufacturing technology is better, easy maintenance. ④ Because of its filler is generally a mixture of asbestos and graphite, so the higher temperature grade. General steam valve with stop valve. Disadvantages: & n