Common valve function and precautions for use (Hebei Innovation Sealing Material Co., Ltd.)
The valve is an important accessory for controlling the flow of the medium on the chemical pipeline. This lecture is more important than the practical application of the valve. The detailed principle and structural sectional view refer to the relevant information books. The valve is composed of three parts: valve body, opening and closing mechanism and valve cover. This paper mainly introduces the structural characteristics of common valves and the precautions for correct use.
First, the type of valve
1. According to the purpose: cut off valves, regulating valves, diverter valves, check valves, safety valves;
2, according to the force points: he uses valves, automatic action valves.
Second, the role of the valve
1. Opening and closing function - cutting or communicating the flow of fluid in the pipe;
2, the adjustment function - adjust the flow rate and flow rate inside the pipe;
3, throttling effect - make a large pressure drop after the fluid passes through the valve;
4, other functions - a. automatic opening and closing b. maintain a certain pressure c. steam barrier drainage.
Third, the main parameters of the valve
PN nominal pressure (the maximum pressure that allows fluid to pass);
DN nominal diameter;
TN temperature range (allows the temperature range of the fluid).
Fourth, the valve before the inspection
Inspection items include:
1. Whether there are defects such as blisters and cracks on the inner and outer surfaces of the valve;
2. Whether the valve seat and the valve body are firmly connected, whether the valve core and the valve seat are in agreement, and whether the sealing surface has defects;
3. Whether the connection between the valve stem and the valve core is flexible and reliable, whether the valve stem is bent or not, and whether the thread is damaged or corroded;
4. Whether the filler and gasket are aging and damaged;
5. Whether the valve opening is flexible or not.
Five, problems often occur in the use of valves
1. Flange and thread leakage at the joint with the pipe;
2. The filler culvert leaks, the lumbar pad leaks and the valve stem does not move;
3. The internal leakage is not strict between the valve core and the valve seat.
6. Characteristics of common valves used in chemical industry and precautions for their use
(a) plug valve (Cock)
Features: TN is less than 150 degrees PN is less than 1.6Mpa, its structure is simple, quick opening and closing, easy operation, small fluid resistance, etc.
Precautions for use:
1. The outer end of the valve stem is square, the straight line marked on the diagonal line is closed and the direction of the valve body is closed, and the direction of the valve body is the same as the open state;
2. The normal switch valve uses a special wrench for the cow to avoid the safety accident caused by the slip of the valve stem; try not to use the adjustable wrench to cause slipping;
3. Open the valve and check according to the previous inspection items. After the inspection, slowly open the valve. When opening, try not to stand in the direction of the sealing surface. Wear an acid-proof mask when encountering acid-base fluid.
The ball valve and the plug valve are the same type of valve, except that the opening and closing member is a ball with a through hole, and the center of the ball is rotated to achieve the purpose of opening and closing. Jacket insulated ball valve, stainless steel ball valve, stainless steel ball valve quick open ball valve
Features: Simple valve structure, reliable operation, used for two-way flow medium pipeline, small fluid resistance, good sealing; Disadvantages: The medium is easy to leak from the valve stem.
Precautions for use:
Same as the plug valve;
With the handle valve, the handle is perpendicular to the flow direction of the medium is closed, and the direction is the same as the open state; if encountering the ball valve with jacket insulation, the following matters should be noted: the jacket insulation steam should be opened to make the valve easy to crystallize. After the medium melts, the valve can be opened and closed. Do not force the valve to open or close when the medium is not completely melted. When the valve cannot be opened, the method of lengthening the arm cannot be used to forcibly open the valve, because this will cause the valve stem to be resisted. Large and the valve core fall off, causing damage to the valve or damage to the wrench, resulting in unsafe factors.
(three) butterfly valve
The butterfly valve uses a rotating disc that can rotate the shaft to control the opening and closing of the pipeline. The size of the corner reflects the degree of opening of the valve.
According to the different transmission modes, the butterfly valve is divided into three types: manual, pneumatic and electric. The common one is manual. The rotary handle drives the valve stem through the gear transmission to open and close the valve.
Features: Butterfly valve has the advantages of simple structure, quick opening and closing, small fluid resistance and convenient maintenance, but it can not be used in high temperature and high pressure applications. PN is less than 1.6Mpa, t is less than 120 degrees of large diameter water, steam,
Air, oil and other pipelines.
Precautions for use:
1. The valve core can only be rotated by 90 degrees. Generally, the direction of the CLOSE and OPEN arrows will be indicated on the valve body. The handwheel rotates clockwise to close, and vice versa.
2, if there is some resistance to opening and closing, you can use a special F wrench to open the valve, but can not force open and close, otherwise the stem gear will be agitated;
3. It is forbidden to remove the handwheel and use the adjustable wrench to pull the valve stem; (the same is true for the valve below)
4. Open and close gradually when opening and closing, observe whether there is any abnormality and prevent leakage.
(four) stop valve
The shut-off valve is the most widely used type of shut-off valve in chemical production. Compared with the above three kinds of shut-off valves, it does not use the rotation of its closing member to open and close the valve, but uses the valve stem to lift and drive the circular shape connected thereto. The valve disc (valve head) changes the distance between the valve disc and the valve seat to achieve the opening and closing of the control valve.
Streamlined globe valve American standard globe valve
Features: The upper part of the stop valve has a hand wheel and a valve stem. The middle part has a threaded and packing culvert sealing section. The small valve stem is threaded in the valve body. The structure is compact, but the valve stem is in contact with the medium, especially the thread part is corroded. Judging from the height of the valve stem exposed bonnet
The structure of the shut-off valve is more complicated, but the operation is simple and not laborious. It is easy to adjust the flow rate and the cut-off passage, and the opening and closing is slow and the hammer is not used, so it is widely used.
When installing the shut-off valve, pay attention to the direction of the fluid, so that the pipeline fluid flows from the bottom to the valve seat, and the so-called "low-in and high-out", the purpose is to reduce the fluid resistance, so that the valve stem and the packing culvert are opened under the labor-saving and closed state. Part of it is not in contact with the medium to ensure that the stem and packing culvert are not damaged or leaked.
The shut-off valve is mainly used for water, steam, compressed air and various materials. It can adjust the flow rate and cut the passage more accurately, but it can not be used for materials with high viscosity and easy to crystallize.
Precautions for use:
1. Check the valve for defects before opening, especially if the filler culvert has leakage;
2. When the valve stem can not be directly rotated by hand, it can be opened and closed with a special F-wrench. When it is still unable to open and close, please do not lengthen the spanner arm to forcibly open and close, thus causing damage to the valve or causing a safety accident;
3. When used in the middle pressure steam pipeline valve, the condensate in the pipe should be drained first, then slowly open the valve with 0.2 to 0.3Mpa steam to preheat the pipeline to avoid sudden rise of pressure. Damage to the sealing surface, adjust the pressure to the desired state when the inspection is normal;
(5) Gate valve
The gate valve is also called the gate valve or the gate valve. It controls the opening and closing of the valve through the lifting and lowering of the gate. The gate is perpendicular to the fluid direction, and the relative position between the gate and the valve seat can be changed to change the channel size.
Open rod type gate valve dark rod gate valve
According to the different movement of the valve stem when the gate valve is opened and closed, the gate valve is divided into two types: the rod type and the dark rod type.
The stem of the stem valve is exposed to the outside of the valve body. When the valve is opened, the stem extends out of the handwheel. The advantage is that the valve opening can be judged according to the outer extension of the stem, the contact length between the stem and the medium is small, and the threaded portion is basically not Affected by the corrosion of the medium, the disadvantage is that the outer space is high.
The threaded stem valve stem thread is designed to fit inside the stem and the internal thread of the gate. When the valve is opened, the stem only rotates without lifting up and down, and the gate rises along the stem. The advantage of the dark-rod gate valve is that the overhanging space is small, and the disadvantage is that the opening of the valve cannot be judged according to the condition of the valve stem, and the valve stem thread is susceptible to corrosion due to long-term contact with the medium.
The gate valve has the advantages of small fluid resistance, constant flow direction of the medium, slow opening without water hammer, easy adjustment of flow rate, etc. The disadvantages are complicated structure, large size, long opening and closing time, and difficulty in repairing the sealing surface. Due to the large diameter water supply pipe
1. When the valve stem is opened and closed in place, it is no longer possible to force the force, otherwise the internal thread or the bolt will be broken to damage the valve;
2. When the valve can not be directly opened when the valve is opened or closed, the F wrench can be used to open and close;
3. Observe the sealing surface of the valve when opening and closing the valve, especially the packing gland to prevent leakage.
(6) Throttle valve
Throttle valve, also known as needle valve, has a shape similar to that of a shut-off valve. Its valve core has a different shape and is tapered or parabolic. It is often used in chemical instruments, often for threaded connections.
Precautions for use:
1. Because of the screw connection, first check whether the threaded connection is loose or not when opening and closing;
2, slowly open and close the valve, because its flow area is small, the flow rate is large, may cause corrosion of the sealing surface, should pay attention to observe, pay attention to changes in pressure.
(7) Check valve
The check valve is a valve that automatically opens and closes by using the pressure difference between the medium before and after the valve, and controls the one-way flow of the medium, which is also called a check valve or a check valve. The check valve is divided into two types: lift type (jumping type) and swing type (shake type) according to the structure.
Lifting type
Precautions for use:
Pay attention to the direction of the valve. The arrow is consistent with the flow direction of the medium. If the medium is easy to crystallize, the valve piece may not be pressed and can not be commanded or stopped.
(eight) safety valve
The safety valve is a valve that automatically opens and closes according to the medium pressure. When the medium pressure exceeds the fixed value, it can automatically open the valve to discharge the pressure, so that the equipment pipeline can be protected from damage. After the pressure returns to normal, it can be automatically closed.
According to the way of balancing the internal pressure, the safety valve is divided into two types: the lever weight type and the spring type.
Precautions for use:
1. The use of the safety valve must be within the validity period of the test;
2. The safety valve control valve installed on the pipeline and equipment is usually that the shut-off valve must be opened to ensure that the safety valve can work effectively;
3. Regularly lift the valve disc slightly, and use the medium to blow the impurities in the valve;
4. If the safety valve cannot work within the set pressure, it must be re-tested or replaced.
(9) Fluoroplastic lined rubber valve
Fluoroplastic rubber-lined valve is mainly used in corrosive medium such as acid and alkali. Its structural principle is similar to that of non-fluorinated plastic valve, except that its valve stem, valve core and valve seat are made of fluoroplastic substrate. .
(10) Traps
The steam trap is a valve that can automatically and intermittently remove the condensed water in the equipment system such as the steam line and the heater, and can prevent the steam from leaking out. Commonly used are bell-shaped float type, thermodynamic type and pulse type.
Precautions for use:
1. Before use, use the pipeline bypass valve to eliminate the condensed water. When there is steam, close the bypass and start the trap with the right way. Otherwise, the valve will not be trapped in the water;
2. Be careful not to be burnt by steam when opening and closing the valve.
(11) Various sampling valves
As a name suggests, sampling valves are valves used to obtain a sample of a medium for chemical analysis. They are generally classified into the following types of equipment or piping: double opening valve, flange clamping valve, and sampling valve with thermal jacket. ;
Use the attention method:
1. The double-opening valve is generally composed of two ball valves, which is safe for sampling and the purpose of sampling by linkage in the negative pressure device; when sampling, the second valve close to the equipment and the pipeline is closed, and the first valve is opened. , 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 in the sampling port to hold the medium;
2. The flange clamp valve is generally sealed by the top cone of the valve stem and the taper hole of the valve seat. When sampling, the valve stem and the cone hole are separated by the rotation of the hand wheel, so that the medium can flow from the cone hole to the outer sampling vessel;
3. The sampling valve with jacket insulation should pay attention to the following items:
The jacket insulation steam should be opened to melt the medium which is easy to crystallize in the valve, and then the valve can be opened and closed. Do not force the valve to open or close without completely melting the medium;
When the valve cannot be opened, the method of lengthening the arm cannot be used to forcibly open the valve, because this will cause the valve stem to be subjected to large resistance and the valve core to fall off, or the valve stem and the tapered hole sealing surface may be damaged, thereby causing the valve. Damage or damage to the wrench, resulting in unsafe factors. (Source: Hebei Innovation Sealing Material Co., Ltd.)
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