Plumbing valve selection and a variety of valve advantages and disadvantages

(A), the valve used on the water supply pipeline, the general principle of choice according to the following: 1, the diameter is not more than 50mm, it is advisable to use a stop valve, pipe diameter greater than 50mm gate valve, butterfly valve. 2, need to adjust the flow, water pressure should be used when the control valve, globe valve. 3, requiring a small flow resistance parts (such as the pump suction pipe), should adopt the gate valve. 4, the flow should be two-way flow of pipe sections should be used gate valve, butterfly valve, shall not use the globe valve. 5, the installation of small parts should adopt the butterfly valve, ball valve. 6, often in the opening and closing of the pipe, should adopt the globe valve. 7, caliber pump outlet pipe should adopt multi-function valve. (B), the following parts of the water supply pipe should be set on the valve: 1, living area water supply pipe from the municipal water supply pipe into the pipe section. 2, residential community outdoor ring network node, should be set to separate requirements. Ring pipe is too long, it is advisable to set up segmented valves. 3, from the living quarters to the water pipe on the branch or pipe from the beginning. 4, household pipe, water meter and each branch standpipe (bottom of standpipe, vertical ring pipe stand up and down end). 5, ring pipe network of sub-trunk, through the branch pipe network connection. 6, indoor water supply pipe to households, public toilets and other access to the beginning of the distribution pipe, water distribution pipe with water points in the 3 and 3 or more settings. 7, the water pump, self-filling pump suction pump. 8, the tank into the outlet pipe, drain pipe. 9, equipment (such as heaters, cooling towers, etc.) water fill pipe. 10, plumbing fixtures (such as large, urinal, wash basin, shower, etc.) with the water pipe. 11, some of the accessories, such as automatic exhaust valve, pressure relief valve, water hammer eliminator, pressure gauge, sprinkler and other front, pressure reducing valve and backflow preventer before and after. 12, the lowest point of the water supply network should set the drain valve. (C), the check valve should generally be installed in accordance with the site, the valve before the water pressure, closed after the closure of the performance requirements and the closure of the water hammer caused by the size and other factors to choose: 1, the valve before the water pressure, Style, ball and shuttle check valve. 2, close the tightness of the performance requirements of close, it is appropriate to use a closed spring check valve. 3, the request to weaken the water hammer off, it should be used to close the anechoic check valve or damping device slowly closing check valve. 4, check valve valve breaking or valve core, should be able to force itself in the gravity or spring off. (D), the following sections of the water supply pipe should be set on the check valve: the introduction of the pipe; closed water heater or water equipment inlet pipe; pump outlet pipe; inlet and outlet pipes combined with a pipe tank, water tower, high ground pool The outlet pipe section. Note: Pipe backflow preventer equipped with pipe sections, do not need to install a check valve. (E), the following parts of the water supply pipe should be set exhaust device: 1, intermittent use of water supply network, the end of the pipe network and the highest point should be set automatically exhaust valve. 2, there is a clear ups and downs of the water supply pipe network of air accumulation, has been set in the peak of automatic exhaust valve or manual valve exhaust. 3, pressure water supply device, when using automatic gas pressure tank, the highest point of its distribution network should be set automatically exhaust valve. Second, the advantages and disadvantages of various valves: Gate valve: gate valve is closed (shutter) along the vertical axis of the channel to move the valve, mainly in the pipeline as a cut-off medium, 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 in 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 will be more than 95%. ② Due to the structure of the butterfly valve and the sealing material, it is not suitable for high temperature and high pressure piping system. General operating 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. The ball valve is mainly used to cut off, distribute and change the medium flow direction in the pipeline. The ball valve designed with V-shaped opening also has good flow regulation 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 natural gas pipeline valve. 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. Considering the long-term use of the case, generally only 120 ℃ do not use. 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: ① due to the flow of medium through the valve has changed, so the minimum flow resistance of the globe valve is also higher than most other types of valves; ② due to longer stroke, the opening speed slower than the ball valve. Plug valve: refers to the closing piece into a plunger-shaped rotary valve, through the 90 ° rotation of the valve plug on the port and the valve port on the mouth connected or disconnected, to achieve a valve on or off. The shape of the plug can be cylindrical or conical. Its principle and the ball valve is basically similar to the ball valve is developed on the basis of the plug valve, which is mainly used for oil field mining, but also for the petrochemical industry. Safety valve: refers to the pressure vessel, equipment or piping, as overpressure protection device. When the pressure in the equipment, container or pipeline exceeds the allowable value, the valve will be automatically opened and then fully discharged to prevent the equipment, container or piping and pressure from rising continuously. When the pressure drops to the specified value, the valve shall automatically Close in time to protect the safe operation of equipment, vessels or lines. Steam Traps: In the delivery of steam, compressed air and other media, there will be some condensation water formed, in order to ensure the work 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 effects: ① can quickly rule out the resulting condensate; ② prevent steam leakage; ③ exclude air and other non-condensable gases. Pressure reducing valve: It adjusts the inlet pressure to a certain required outlet pressure and relies on the energy of the medium itself to make the outlet pressure keep stable automatically. 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, which belongs to an automatic valve. Check valve for piping systems, its main role is to prevent media backflow, to prevent the pump and drive motor reversal, and the release of container media. Check valves can also be used on lines where the pressure may rise above the system pressure on the auxiliary system. The main can be divided into swing-type (according to the center of gravity rotation) and the lift (along the axis of movement).

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