Tumfei Valve Technology：The principle of common valves and their use

　　Tumfei Valve Technology has summarized the principle of common valves and their use. Let's learn about them together.

　　First, the role of the valve

　　1, opening and closing action - cut off or communicate the flow of fluid in the tube;

　　2, regulating effect - regulating tube flow, flow rate;

　　3, throttling effect - make the fluid through the valve to produce a large pressure drop;

　　4. Other functions -a. Automatic opening and closing b. Maintain a certain pressure c, prevent steam drainage.

　　Second, the type of valve

　　1, according to the use of: cut-off valves, regulating valves, diverting valves, check valves, safety valves;

　　2, according to the force points: he action with the valve, automatic action valve.

　　Three, the main parameters of the valve

　　PN nominal pressure (the maximum pressure that allows fluid to pass through);

　　DN nominal diameter;

　　TN Temperature range (permissible fluid temperature range).

　　Forth， Check the valve before use

　　Check items include:

　　1, the internal and external surfaces of the valve body have sand holes, cracks and other defects;

　　2. Whether the valve seat is firmly engaged with the valve body, whether the spool is consistent with the valve seat, and whether the sealing surface is defective;

　　3, whether the valve stem and the spool connection is flexible and reliable, whether the valve stem is bent, whether the thread is damaged or corroded;

　　4, packing, gasket is aging damage;

　　5, the valve open is flexible, etc.

　　Fifth，Problems often occur in the use of valves

　　1, flange and thread leakage at the connection of the pipeline;

　　2, packing culvert leakage, waist pad leakage and valve stem can not move;

　　3, between the valve core and the seat is not tightly closed to form internal leakage.

　　Sixth, the characteristics of commonly used valves and their use precautions

　　(1) Plug Valve (Cock)

　　Features: TN less than 150 degrees PN less than 1.6Mpa its simple structure, quick opening and closing, easy operation, low fluid resistance and other advantages

　　Precautions for use:

　　1, the outer end of the valve stem is square, the straight line marked by the diagonal is vertical and the direction of the valve body is closed, and the direction of the valve body is consistent with the open state;

　　2, the normal switch valve with cock special wrench, to avoid sliding with the valve stem caused by safety accidents; Try not to use an adjustable wrench to cause slippage;

　　3, open the valve according to the previous check item check, slowly open the valve after the check, try not to stand in the direction of the sealing surface when opening, encounter acid and alkali fluid must wear acid mask;

　　4, if the pipeline has a sight mirror see the fluid in the sight mirror can be checked and left.

　　(2) Ball valve:

　　Ball valve and plug valve are the same type of valve, but the opening and closing part is a ball with a hole, and the center line of the ball valve stem rotates 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: Valve structure is simple, reliable, used for two-way flow medium pipeline, fluid resistance is small, good sealing; Disadvantages; The medium is easy to leak from the stem.

　　Precautions for use:

　　Same as a plug valve;

　　With a handle valve, the handle perpendicular to the medium flow direction for the closed state, consistent with the direction for the open state; If the ball valve with jacket insulation should pay attention to the following matters:

　　The jacket insulation steam should be opened to melt the crystallizing medium in the valve before opening and closing the valve, do not forcibly open and close the valve before the medium is completely melted;

　　When the valve cannot be opened, the method of lengthening the lever cannot be used to forcibly open the valve, because this will cause the valve stem to be resisted and the spool to fall off, causing damage to the valve or causing damage to the wrench, resulting in unsafe factors.

　　(3) Butterfly valve

　　The butterfly valve uses a rotating disc with a flexible shaft to control the opening and cosing of the pipeline, and the Angle size reflects the opening degree of the valve.

　　According to the different transmission methods, the butterfly valve is split, pneumatic and electric three, commonly used for manual, rotating handle through the gear drive valve stem to open and close the valve.

　　Features: Butterfly valve has the advantages of simple structure, rapid opening and closing, small fluid resistance, easy maintenance, etc., but it can not be used for high temperature and high pressure occasions, PN less than 1.6Mpa, t less than 120 degrees of large diameter water, steam, air, oil and other pipelines.

　　Precautions for use:

　　1, the spool can only be rotated 90 degrees, generally the valve body will indicate the direction of the CLOSE and OPEN arrows, the hand wheel clockwise rotation is closed, and the reverse is open;

　　2, if sometimes there is a certain resistance to opening and closing, you can use a special P wrench to open the valve. But it can not be forced to open and close, otherwise the male will stir the thin rod gear:

　　3. It is forbidden to remove the handwheel and report the hand vibration valve sample with activity; (Same goes for lower waist)

　　4. Gradually open and close when opening and closing, observe whether there is any abnormal situation, and prevent leakage.

　　(4) Stop valve

　　The globe valve is the most widely used cut-off valve in chemical production. Compared with the above three cut-off valves, it is not the use of the rotation of its closing parts to open and close the valve, but the use of the valve stem to drive the circular valve disc (valve head) connected with it, and change the distance between the valve disc and the seat to control the valve opening and closing.

　　Streamline type stop valve American standard stop valve

　　Features: The upper part of the globe valve has a handwheel, valve stem, the middle has a thread and packing culvert sealing section, the small valve stem on the thread in the valve body, its compact structure, but the valve stem and the medium contact part, especially the thread part is easy to corroded, from the height of the valve stem exposed to the valve cover can be judged

　　The globe valve structure is more complex, but the operation is simple, not very laborious, easy to adjust the flow rate and truncate the channel, slow closing without water hammer phenomenon, so it is more widely used.

　　When installing the globe valve, pay attention to the direction of the fluid, the pipeline fluid should flow through the valve seat from the bottom up, and the so-called "low into high", the purpose is to reduce the fluid resistance, so that the valve stem and packing culvert are not in contact with the medium under the opening and closing state, to ensure that the valve stem and packing culvert are not damaged and leaked.

　　The globe valve is mainly used for the pipeline of water, steam, compressed air and various materials, which can adjust the flow rate more accurately and strictly cut off the channel, but can not be used for materials with large viscosity and easy crystallization.

　　Precautions for use:

　　1, before opening to check the valve for defects, especially the filler culvert leakage:

　　2, in the valve stem can not be directly rotated by hand, the special F wrench can be used to open and close, when it is still unable to open and close, please do not extend the wrench lever to force open and close, resulting in damage to the valve or cause safety accidents:

　　3, when used for medium pressure steam pipeline valve, the condensate in the pipe should be drained first when opened. Then slowly open the valve with 0.2 to 0.3Mpa steam to preheat the pipeline, to avoid the sudden opening of pressure caused by damage to the sealing surface, called the normal inspection after the pressure to adjust the required state

　　(5) Gate valve

　　Gate valve, also known as gate valve or gate valve, it is through the lift of the gate to control the valve opening and closing, the gate is straight to the direction of the fluid, change the relative position between the gate and the seat can change the size of the channel.

　　Open stem gate valve Dark stem gate valve

　　According to the different movement of the valve stem when the gate valve is opened and closed, the gate valve has two kinds of distinct rod type and dark rod type.

　　Open rod gate valve stem thread strike outside the valve body, open the valve stem out of the handwheel, its advantage is that according to the length of the valve stem to determine the size of the valve open, the valve stem and the medium contact length is small, the thread part is basically not affected by the medium corrosion, the disadvantage is that the height of the overhang space.

　　The valve stem thread inside the valve stem and the internal thread on the gate plate want to match, open the valve stem only rotation without up and down, the gate rises along the valve stem thread. The advantage of dark rod gate valve is that the overhang space is small, the disadvantage is that the opening of the valve can not be judged according to the condition of the valve stem, and the valve stem thread is easily corroded by long-term contact with the medium.

　　Gate valve has the advantages of small fluid resistance, constant medium flow direction, slow opening without water hammer phenomenon, easy to adjust the flow rate, etc. The disadvantages are complex structure, large size, long opening and closing time, and difficult maintenance of sealing surface. Due to the large bore feed pipe

　　1, when the valve stem is opened and closed in place, it can not be forced to force, otherwise it will break the internal thread or latch screw, so that the valve is damaged;

　　2, open and close the valve when the hand can not be directly started, F wrench can be used to open and close;

　　3. When opening and closing the valve, pay attention to the sealing surface of the valve, especially the packing gland to prevent leakage.

　　(6) Throttle valve

　　Throttle valve, also known as needle valve, its shape is similar to the globe valve, its valve core shape is different, back to the base or parabola, often used in the instrument, often bundle connection.

　　Precautions for use:

　　1, because of the threaded connection, first check whether the threaded connection is loose when opening and closing;

　　2, open and close the valve slowly, because the flow area is small, the flow rate is large, may cause corrosion of the sealing surface, should pay attention to observe, pay attention to the change of pressure.

　　(7) Check valve

　　Check valve is a valve that automatically opens and closes by using the pressure difference between the medium before and after the valve to control the one-way flow of the medium, also known as check valve or check valve.

　　Check valves are divided into two types according to different structures: lifting type (jumping type) and swinging type (shaking pole type).

　　Lift type swing type

　　Precautions for use:

　　Pay attention to the direction of the valve, the arrow is consistent with the flow direction of the medium, such as the medium easy crystallization may cause the valve disc can not be pressed down to play the role of command and check.

　　(8) Safety valve

　　The safety valve is a kind of valve that automatically opens and closes according to the medium pressure. When the medium pressure exceeds a certain value, it can automatically open the valve to discharge pressure relief, so that the equipment pipeline is free from the danger of damage, and can automatically close after the pressure returns to normal.

　　According to the way of balancing the internal pressure, the safety valve is divided into two categories: lever weight type and spring type.

　　Precautions for use:

　　1, the safety valve must be used within the validity period;

　　2, the safety valve control valve installed on the pipeline and equipment is usually the globe valve must be opened to ensure that the safety valve can work effectively;

　　3. Periodically lift the valve disc slightly and use the medium to blow the impurities in the valve.

　　4, if the safety valve can not work within the setting pressure, it must be re-validated or replaced

　　(9) Steam trap

　　Steam trap is a kind of valve that can automatically and intermittently remove condensate and prevent steam from leaking out in steam pipeline, heater and other equipment systems. Commonly used are bell-shaped float type, thermal power type and pulse type.

　　Precautions for use:

　　1, use the pipeline bypass valve to remove condensate before use, when there is steam to close the bypass, start the trap path, otherwise the valve will be closed water can not play the role of drainage;

　　2. Be careful not to be scalded by steam when opening and closing the valve.

　　(10) All kinds of sampling valves

　　As the name suggests, the sampling valve is a valve used to obtain media samples so that chemical analysis can be performed, generally installed in equipment or pipelines are roughly divided into the following categories:

　　Double opening valves, flanged clip valves, and sampling valves with insulated jacket:

　　Use note method:

　　1, the double opening valve is generally composed of two ball valves, to sample safety and achieve the purpose of sampling through linkage in the negative pressure device; When sampling, close the second valve near the equipment and pipeline and open the first valve. Let the medium flow into the space between the two valves; Then close the first valve, open the second valve, and place the sampling vessel into the sampling port to contain the medium;

　　2. The flange clip valve is generally sealed through the top cone of the valve stem and the cone hole of the seat, and the valve stem is separated from the cone hole by turning the hand wheel during sampling, so that the medium can flow from the cone hole to the external sampling vessel;

　　3, with jacket insulation sampling valve should pay attention to the following matters:

　　I should open the jacket insulation steam to melt the crystallizable medium in the valve before opening and closing the valve, do not forcibly open and close the valve before the medium is completely melted;

　　When the valve cannot be opened, the method of lengthening the lever cannot be used to forcibly open the valve, because this will cause the valve stem to suffer greater resistance and the valve core to fall off, or cause the valve stem and the cone hole sealing surface to be damaged. from

　　And cause damage to the valve or cause damage to the wrench, resulting in unsafe factors.

　　(11) Fluorine plastic lined rubber valve

　　Fluorine plastic lined rubber valve is mainly used in acid and alkali and other corrosive media, its structure principle is similar to the unlined fluorine plastic valve, but its stem, valve core, valve seat are used fluorine plastic substrate, its use method is similar.

　　Classification of valves

　　There are many kinds of valves. With the continuous improvement of the process flow and performance of various complete sets of equipment, the types of valves are still increasing, and there are a variety of classification methods.

　　According to the automatic and drive classification, can be divided into:

　　1) Automatic valves rely on the ability of the medium (liquid, air, steam, etc.) to operate by itself. Such as safety valves, check valves, pressure reducing valves, steam traps, solenoid valves, air traps, emergency cut-off valves, etc.

　　2) Drive valves Valves that are operated manually, electrically, hydraulically or pneumatic. Such as gate valve, globe valve, throttle valve, butterfly valve, ball valve, plug valve and so on.

　　According to the use and function classification, can be divided into:

　　1) The cut-off valve is mainly used to cut off or connect the medium flow in the pipeline. Such as globe valve, gate valve, ball valve, plug valve, butterfly valve, diaphragm valve and so on.

　　2) Check valves are used to prevent the backflow of the medium. Such as a variety of different structures of the check valve.

　　3) Regulating valves are mainly used to regulate the pressure and flow of the pipeline medium. Such as regulating valve, throttle valve, pressure reducing valve and so on.

　　4) The diverter valve is used to change the direction of the flow of the medium in the pipeline, and plays the role of distributing, diverting or mixing the medium.

　　Such as various structures of distribution valves, three-way or four-way plug valves, three-way or four-way ball valves, various types of traps and so on.

　　5) Safety valves are used for overpressure safety protection, discharge of excess media, and prevent pressure from exceeding the specified value. Such as various types of safety valves.

　　6) Multi-purpose valves are used to replace two, three or even more types of valves. Such as stop check valve, check ball valve, stop check safety valve, etc.

　　7) Other special valves such as blowdown valve, blowdown valve, coke valve, pigging valve, etc.