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Valve is a chemical pipeline to control the flow of media is an important annex, this lecture is more important than the practical application of the valve, the detailed principles and structure of the cross-sectional reference to the relevant information books, valves from the valve body, opening and closing institutions, the valve cover three major components, this Focus on the company's common structural features of the valve and the correct use of precautions. First, the role of the valve 1, the role of opening and closing - cut off or communicate the flow of fluid within the tube; 2, the regulatory role - to regulate the flow of the tube, the flow rate; 3, throttling effect - the fluid through the valve have a great pressure drop ; 4, other functions - a. Automatic opening and closing b. To maintain a certain pressure c. Second, the type of valve 1, according to the use points: cut-off valves, regulating valves, diverting valves, check valves, safety valves; * Third, the main parameters of the valve PN nominal pressure ); DN nominal diameter; TN temperature range (temperature range of fluid allowed). Fourth, the use of the valve before the inspection items include: 1, the valve body inside and outside the surface with or without trachoma, cracks and other defects; 2, the valve seat and the valve body is solid, the valve plug and valve seat is consistent, sealing surface without defects; 3, the stem and the spool connection is flexible and reliable, the valve stem bending, thread damage, corrosion; 4, packing, washer aging damage; 5, valve opening is flexible and so on. Fifth, the valve often used in the process of problems 1, and pipe connections at the flange, thread leakage; 2, culvert leakage, waist pad leakage and stem open; 3, the valve core and the valve between the formation of lax Leak inside. Sixth, the characteristics of chemical common valves and their precautions (A) Plug Valve (Cork) Features: TN less than 150 degrees PN less than 1.6Mpa Its simple structure, quick opening and closing, easy operation, low fluid resistance Advantages : 1, the outer end of the stem is square, diagonal lines marked vertical and the direction of the valve is closed, consistent with the direction of the valve is open; 2, the normal switch valve with Cork special wrench to avoid slipping with the stem 3, open the valve according to the inspection items in front of inspection, open the valve slowly after opening, try not to stand on the sealing surface when opening direction, encountered acid and alkali fluid to wear when the anti- Acid mask; ball valve and plug valve is the same type of valve, but its opening and closing pieces with a through-hole ball, ball Rao stem centerline rotation to achieve the purpose of opening and closing. Insulated ball valve with jacket Stainless steel ball valve Stainless steel ball valve Quick opening ball valve Features: The valve structure is simple, reliable, for two-way flow medium pipeline, small fluid resistance, good sealing; Disadvantages: medium easily leak from the stem part. Caution: The same as the plug valve; with a handle valve, the handle perpendicular to the flow direction of the medium is closed, consistent with the direction of the open state; in the event of a ball valve with jacket insulation should note the following: The jacket should be Insulation steam to open the valve is easy to crystallize the medium melt before opening and closing the valve, do not force the media is not fully melted to open and close the valve; when the valve can not be opened, you can not use the method of lengthening the force arm, forcibly open the valve because This will result in greater resistance stem stem and valve off, resulting in damage to the valve or cause damage to the wrench, resulting in insecurity. (C) butterfly valve butterfly valve is the use of a can rotate the disc to control the opening and closing of the pipeline, the size of the corner reflects the degree of opening the valve. According to the transmission mode different butterfly valve sub-manual, pneumatic and electric and other three, commonly used for manual, rotary handle through the gear drive to move the valve stem to close the valve. Features: Butterfly valve has the advantages of simple structure, rapid opening and closing, small fluid resistance, easy maintenance and other advantages, but can not be used in high temperature and high pressure occasions. Large diameter water, steam, air, oil, etc. of PN less than 1.6Mpa and t less than 120degree. Pipeline. Caution: 1, the spool can only rotate 90 degrees, the general body will indicate CLOSE and OPEN arrow direction, hand wheel clockwise turn off, on the contrary open; 2, open and close if there is a certain resistance, you can use Special F wrench open the valve, but can not be forced to open and close, otherwise it will spoil the valve stem gear; 3, prohibit the removal of the hand wheel with an adjustable wrench to pull the valve stem; (The following valve is the same) 4, Close, observe whether there is any abnormal situation and prevent leakage. (D) Globe Valve Globe valve is the most widely used chemical production of a truncated valve, which is not compared with the aforementioned three cut-off valve is the use of its rotation of the closure open, close the valve, but the use of stem lift and drive Connected to the valve plate (valve head), change the distance between the valve plate and the valve seat to control the valve closed. Flowline globe valve American standard stop valve features: the upper part of the valve hand wheel, stem, the middle of the thread and packing culvert seal, the small valve stem on the thread in the valve body, its compact structure, but the stem and the media The contact part is more, especially the thread part is easy to corrode. The height of the bonnet exposed from the valve rod can judge the structure of the stop valve is complex, but the operation is simple and easy, the flow is easy to be adjusted and the channel is cut off. Use more widely. Stop valve installation should pay attention to the fluid direction, should make the pipeline fluid flow from the bottom up through the valve seat port, and the so-called "low into high," the purpose is to reduce fluid resistance, so that open the labor-saving and closed stem, filler culvert Some do not come into contact with the medium, to ensure that the stem and packing culvert will not be damaged and leaked. Globe valve is mainly used for water, steam, compressed air and various materials pipeline, can be more accurately regulate the flow and cut off the channel, but not for viscosity, easy to crystallize the material. Note: 1, check the valve before opening without defects, in particular, there is no leakage of packing culvert; 2, the stem can not be directly rotated by hand, the special F wrench can be used to open and close, when still unable to open and close, please Do not lengthen the wrench arm to forcibly open and close, resulting in damage to the valve or cause a safety accident; 3, when used in medium pressure steam pipe valve, open the drain pipe should be the first drain, and then slowly the valve Open with 0.2 to 0.3Mpa steam pipe preheating, to avoid sudden pressure rise caused by the sealing surface damage, when the normal pressure will be adjusted to the desired state; (five) gate valve, also known as the gate valve or gate valve , It is through the gate to control the valve lift opening and closing, gate perpendicular to the fluid direction, changing the relative position between the gate and the valve seat to change the channel size. Ming-rod gate valve dark-rod valve gate valve opening and closing according to the different movement of the stem, the gate valve is also clearly two kinds of rod and dark rod. Ming rod stem valve stem thread exposed outside the body, open the valve stem stick out the handwheel, the advantage of the stem can be extended according to the length of the valve to determine the size of the valve stem contact with the media length is small, the thread part of the basic Affected by the medium of corrosion, the disadvantage is that the height of the extension of large space. Dark rod gate valve stem thread inside the gate with the internal thread on the gate to cooperate, open the valve stem rotation only without lifting, the gate along the stem thread rise. Dark bar gate valve advantage is the small extension, the disadvantage is that the valve can not be judged according to the valve stem open, the valve stem long-term exposure to the media and susceptible to corrosion. Gate valve has the advantages of small fluid resistance, constant flow of medium, open slow water hammer, easy to adjust the flow, etc. The disadvantage is the complex structure, larger size, longer opening and closing time, sealing surface maintenance difficulties. Because of the large diameter of the water supply pipe 1, when the valve stem opening and closing in place, you can no longer force, otherwise it will pull off the internal thread or bolt screws, so that the valve damage; 2, open the valve can not directly start when the hand can be used to open the F wrench Closed; 3, open and close the valve observe the valve sealing surface, especially at the packing gland to prevent leakage. (F) throttle Throttle valve, also known as needle valve, its shape and cut-off valve similar to the different shape of the spool, was tapered or parabolic shaped, commonly used in chemical instrumentation, often threaded connection. Precautions for use: 1, because of the threaded connection, it is the first to check whether the screw connection is loose when opening and closing; 2, the slow opening and closing the valve, because of its smaller flow area, larger flow rate, may cause the sealing surface corrosion, should Watch carefully and pay attention to changes in stress. (G) check valve Check valve is the use of valve pressure difference before and after the media automatically open and close, control the flow of media one-way valve, also known as non-return valve or check valve. Check valve according to different structure is divided into lift (hop-heart-type) and swing-type (shake pole) two. Lift Swing Use caution: pay attention to the direction of the valve, the arrowhead and the medium flow direction, such as the medium easy to crystallize may cause the valve can not be depressed can not command, check the role. (Viii) Safety valve Safety valve is a kind of automatically open and close the valve according to the medium pressure, when the medium pressure exceeds the set value, it can automatically open the valve discharge pressure relief, the equipment pipeline from the risk of damage, the pressure back to normal Can automatically shut down. According to the different ways of balancing the internal pressure, safety valve is divided into two types of lever hammer and spring. Caution: 1, the use of safety valves must be valid within the validity period; 2, piping, equipment installed on the safety valve control valve is usually the globe valve must be opened to ensure the safety valve can work effectively; 3, , With the media to blow valve impurities. 4, If the safety valve can not work within the set pressure, it must be revalidated or replaced. (9) Trap Trap is a system of steam pipes, heaters and other equipment that automatically and intermittently drain condensate water and prevent steam leakage A kind of valve There are commonly used bell-shaped float, thermal and pulse several. Caution: 1, Before using the pipe bypass valve to exclude condensate, turn off the bypass when there is steam, use the trap right way, otherwise the valve will be closed to play the role of hydrophobic water; 2, when the valve is closed Be careful not to be scalded by steam. (X) all kinds of sampling valve sampling valve as the name suggests is used to obtain samples of the media can be chemical analysis of the valve, generally installed in the equipment or pipe can be divided into the following categories: double open valve, flange clip valves, and Sampling valve with insulation jacket; Precautions for use: 1. Double opening valve is generally composed of two ball valves, which play the role of sampling safety and achieving the purpose of sampling through the linkage in negative pressure device. When sampling, close to the equipment and piping Of the second valve is closed, open the first valve, so that the medium flow to the space between the two valves; and then close the first valve, open the second valve, the sampling vessel placed sampling port containing medium; 2, the flange Clip valve is generally sealed by the top of the valve cone and valve seat taper hole, the sample is rotated by the hand wheel to the stem and cone hole from the cone so that the media can flow to the external sampling vessel; 3, with a jacket Insulated sampling valve should pay attention to the following: I should heat insulation jacket open the valve will be easy to crystallize the medium melt before opening and closing the valve, do not medium Not fully melt on the open and close the valve; Î when the valve can not be opened, you can not use the method of lengthening the force arm, forcibly open the valve, because this will result in greater resistance stem and valve stem off, or cause stem And tapered bore sealing surface damage, resulting in damage to the valve or cause wrench damage, resulting in insecurity. (11) Fluorine Plastic Lining Valve Fluorine plastic lined valve is mainly used in acid-base and other corrosive medium. Its structural principle is similar to that of fluorine-free plastic valve except that its valve stem, valve core and valve seat are all used Fluorine plastic substrate, its use is similar. Search Keyword: More Valve Technical Articles