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1. Preface Valves are used in piping systems to handle liquid controls. The first step in choosing a valve is to know the function of the various valves and the valve we want, and to accomplish the tasks and effects we have entrusted with. 2. Valve classification (1) According to its function, the valve is classified as follows: Switch valves: gate valve, plug valve, ball valve. B. Throttle class: ball valve, needle valve, angle valve, disc valve, diaphragm valve. C. Check valves: swing, lift and two-piece check valve, the end of the valve. D. Pressure control valves: pressure reducing valve, pressure relief valve, safety valve. E. Special valves: a. Sampling valve b. Flow Control Valve c. Drain valve d. Non-metallic valves: PVC, plastic (steel), Teflon and so on. B. Metal valves a. Iron metal: iron, steel, stainless steel, alloy steel. b. non-metallic: aluminum, copper and so on. (3) way classification Casting valves: sand mold, shell mold, wax mold, casting and other modeling methods, the production of valve parts. B. Forging valves: by forging or free forging or pellets (party) value of the value of processing, the production of valve parts. C. WELDING MANUFACTURING VALVE: The body and the cover are each made of a combination of several parts. Such valves must be specified for the welding procedure and its qualification (WPS and PQR). D. Injection molding valves: generally used in PVC, plastic to be non-metallic valve manufacturing. 3. Characteristics of various types of valves (1) GATE VALVES gate valve is designed to be used in a system where a part of a pipeline needs to be "fully open, fully closed" control and fluid flow can only be generated with a slight pressure drop. Gate valves are ideal and suitable when a part of a system needs to be isolated, regardless of THROTTING control. When the throttle when used, the fluid will flow through the door at high speed, resulting in fluid erosion door, seat and shell (resulting in drawing phenomenon), or cause vibration and damage. (2) GLOBE VALVES, ANGLE VALVES, NEEDLE VALVE Ball valves are known for their ball-and-ball shape, mainly for tightness, frequent switching, and when fluid To control the flow of the throttling effect of the design, the most important feature is the effective throttle, so that the phenomenon of drawing to a minimum and thus reduce the valve and seat dip (red) corrosion, but the seat is parallel to the streamline, fluid Flow through the valve seat when the change will produce spoiler in the valve, as well as the decline in force, only because of the pressure drop caused by the loss of head lift, before use. Angle valve structure, characteristics are modified by the ball valve, only the outlet and into the 90 degrees at right angles to the difference. Needle valve is also modified by the plug ball valve, the plug is elongated tapered needle, especially for low flow range of flow control. (3) CHECK VALVES ----- SWING TYPE, LIFT TYPE, TILTING DISC, DUALPLATE, FOOT VALVE FOOT VALVES). The role of such valves to allow free flow of fluid in one direction, and to limit the backflow, when the fluid pressure through the system, the valve open, the reverse of any fluid, the valve will be closed, the completion of the closure, is to rely on the back The weight of the mechanism or the back pressure, or rely on the spring or rely on a combination of the above. (4) GLOBE STOP-CHECK VALVES The check valve is a lift check valve similar to item 3.3 except that the valve stem and hand-operated input (or other auxiliary operating devices) are installed to shut off the fluid And check back, check valve can not be opened by any mechanical transmission, only by the upstream fluid pressure valve lift, leaving the valve seat surface. (5) plug valve (PLUG VALVES) This valve is inserted into the valve body by the valve (door), for a taper of the middle slotted plug member named, the simple structure of the ancient type of valve, from the fully open to close Only need to turn 90 degrees, the valve plug (door) of the flow can be any size and shape, can also be made porous type with three or four pipe connections, but can have different flow combinations. Generally used for fully open or closed, without throttling (unless the opening special diamond shape and processed). (6) BALL VALVE The ball valve is modified by the plug valve to replace the plunger with a ball plug to control the liquid. The cross-sectional area of ​​the passage in the valve plug (door) is the same as the diameter of the mating pipe. The fluid is straight Through the body, and sucked with a slight pressure drop. Are generally used PTEE, EPDM and other materials for the valve seat, therefore, good bubble sealing. And improved for fire safety and anti-static design, is widely used, but the seat for the PTFE material, the temperature is generally limited to 250 degrees below. (7) BUTTERFLY VALVES This valve structure, is based on the principle of the tube baffle, the flow control element is a tilt plate (door) (which can be made of metal or metal cladding plastic, Teflon, etc.), the disc is fixed on the mandrel, and the rotatable mandrel to control the opening and closing (open, closed only 90 degrees of rotation), the valve seat for the metal, rubber, Teflon and other materials, Which is fixed on the valve body wall. The valve is simple in structure and the valve body is of the WAFER type. The utility model has the advantages of light weight and space saving, and is suitable for throttling and opening and closing. Especially for large flow control (not suitable for small flow). (8) Diaphragm valve (DIAPHRAGM VALVES) This valve is really nothing more than a "clincher" valve, a flexible, disturbing membrane attached to the compression element by a helix and operated by a valve stem Move up and down, as the compression element rises, the diaphragm will lift and cause passage. When the compression element is lowered, the diaphragm will press against the valve body weir (if weir type valve) or at the bottom of the contour (assuming straight through) This valve is suitable for switching and throttling purposes. Diaphragm valves are particularly suitable for transporting corrosive, viscous fluids such as slurries, food, pharmaceuticals, weaving, etc. Because of the pipeline, the operating mechanism of the valve is not exposed to the transport fluid Non-polluting, no filler required, stem packing never leaks. (9) SAFETY BALVES, RELIDF VALVES, SAFETY, PRESSURE RELIEF VALVES There is a considerable opportunity to use high temperature and pressure gas in the plant, especially in power plants and chemical plants where the pressure in the column , Boilers, pipelines and other pressure vessels, the equipment is destroyed and leaks, the probability of fire or explosion is quite high. In order to prevent such accidents, the process of stable operation, according to the American Society of Mechanical Engineers (ASME), must be at All high-pressure equipment is fitted with these safety venting valves. Such valve structure similar to the angle valve, according to the different modes of operation can be divided into the spring loaded load (SPRING LOADED TYPE) and auxiliary valve actuated (PILOT OPERATED TYPE). Basically, the device is driven by the balance of power. Once the pressure on the valve disc (door) is greater than the set pressure of the bomb or auxiliary valve, the valve disc will be pushed away by this pressure and the gas (liquid) in the pressure vessel will be expelled to lower the pressure vessel Pressure inside. The safety valve shall be designed to function as a fully open emergency vent whose capacity overpressure and flushing must be governed by the ASME Code. Pressure relief valve, designed to increase the initial pressure, the valve slowly open, and there is no law as the basis, it does not have to open immediately to the fully open position, but the pressure increases, it should continue to open. (10) CRYOGENIC VALVES For transportation of liquefied gases (oxygen, nitrogen, hydrogen, helium) in refrigerated locations usually made of bronze or 300 series stainless steel, in the form of a valve that can be a gate valve, ball type Valve, ball valve, needle valve, disc valve, the valve is different from the above common valve treatment, one is extended bonnet, so designed, is to have a sufficient gas chamber to prevent stem packing frozen , And affect the operation and sealing, and reduce the heat leakage through the valve stem, but also between the pipeline and hands to lose, providing adiabatic space, and the other is in the closed double-seat cavity inside the closed hole must be Consider excretion of liquefied gas into the gas to avoid excessive pressure. (11) Other special valves, listed below, do not make one by one introduction. A. Sampling valve B. Bottom tank flush valve. Pressure reducing valve Back pressure adjustment valve E. Solenoid valve Control valve 4. Selection of the key points Valuable selection of valves to be used in accordance with the following procedures, one by one inspection, so be selected with the valve in order to meet their functions, the implementation of the tasks delivered. (1) the characteristics of the valve and the main executive function Understand the characteristics of various types of valves and their executive function, the first step for the selection of suitable valves, the characteristics of various types of valves, classification and the main executive function in front of 2, 3 As mentioned in the section, it is summarized as Table I and Table II for reference. (2) caliber or flow (volume) "Table III shows" The nominal diameter of the valve, which is not necessarily the same as the diameter of the flow path, is chosen so that the required Cv value is calculated from the condition of the delivered fluid and then the caliber of the suitable valve is selected from the Cv value (see manufacturer's catalog). B. The Cv value is defined as the Cv value measured per minute at a pressure drop of 1 at 60 degrees Fahrenheit after the water has passed through the valve. C. Cv value can be calculated through the valve flow (Q). Q = CvΔP = 7.9Cv P = liquid density, LB / FT3 ΔP = pressure drop after passage through the valve, PSI (3) Temperature VS The "temperature VS pressure" of the pressure valve is the value specified by the valve at a given temperature Permissible and safe pressure (but this pressure is the maximum permissible pressure without impact). 5. Valve structure material Valve structure of the material selection, the functional life of the valve can be extremely important, but the general structure of the valve material is divided into two main categories: Pressure main material: body, bonnet, bottom cover, bolts and so on. Pressure main material selection Main factors considered: a. Fluid temperature, pressure: A) high temperature use: metal materials generally in high temperature environment, its tensile strength and life expectancy decreases with increasing temperature, the latent change The strength also has an impact. B) low temperature use: metal materials at low temperatures in the use of occasions, the sharp decline in its toughness to produce low temperature brittleness phenomenon. b. Corrosion resistance of the material: Causes of valve structure metal corrosion: (A) Fluid type (B) Concentration (C) Temperature Corrosion Damage form: (A) And stripping (D) Intergranular corrosion (E) cracking c. Erosion resistance of materials: Generally, erosion resistant materials must have the following features: A) strong oxide film material B) Material with high fatigue limit D) Material with higher hardness B. TRIIM: Main parts such as valve seat, valve seat, stem, guide bush and internal small parts Material selection Considerations: a) fluid temperature b) material corrosion resistance c) material erosion resistance d) material wear resistance and anti-viscosity (6) bonnet form General bonnet and valve body combination, there are the following, according to Valve size, usage conditions, temperature and pressure and leakage caused by the risk of other conditions, for its evaluation options. A. SCREWED BONNET B. Bolt bonded (BOLTED BONNET) C. Weld combined (SEAL WELDED BONNET) D. Pressure-sealed (PRESSURE SEAL BONNET) E. The special requirements of the valve structure by the UNION TYPE (7) are different depending on the temperature and the place of application. Special requirements are listed as follows: A. Fireproof and anti-static design - special attention must be paid to the design and usage of the ball valve. B. Extended bonnet design - used in freezing valve, conveying liquefied gas. C. Noise and Cavitation Restrictions - Especially for control valve design and use of special considerations. D. Anti-filler leakage of the retractable capsule reference design - to be absolutely closed, no place to consider. 4.8 mode of operation is generally limited to the installation environment, operation, operating conditions or the number of times, with electric and pneumatic drive considerations, and due to the popularity of computer applications, and development to the entire system process connection and monitoring, without human-driven . However, most of them are still willing to adopt the economy and durability of the wheel or gear reducer.