guidance on selection of all kinds of valves
gate valve
The gate valve is used as a cut-off medium, and the whole circulation is straight when it is fully opened, at which time the pressure loss of the medium operation is minimal. Gate valves are usually suitable for working conditions that do not need to be opened and closed frequently and keep the gate fully open or closed. Not suitable for regulating or throttling. For high-speed flowing media, the gate can vibrate when it is partially opened, and the vibration may damage the sealing surfaces of the gate and the valve seat, while throttling will make the gate suffer from media erosion. From the structural form, the main difference is the form of sealing element adopted. According to the form of sealing elements, gate valves are often divided into several different types, such as wedge gate valves, parallel gate valves, parallel double gate valves, wedge double gate valves and so on. The most commonly used form is wedge gate valve and parallel gate valve.
globe valve
The axis of the stem of globe valve is perpendicular to the sealing surface of the valve seat. The opening or closing stroke of the valve stem is relatively short, and it has very reliable cutting action, which makes this valve very suitable for cutting off or adjusting the medium and throttling. Once the disc of cut-off valve is in the open state, its valve seat and disc sealing surface are no longer in contact, and it has very reliable cutting action, so this valve is very suitable for cutting off or regulating medium and throttling.
once the globe valve is in the open state, there is no contact between the valve seat and the sealing surface of the disc, so the mechanical wear of the sealing surface is small. Because the valve seat and disc of most globe valves are easy to repair or replace the sealing element, it is not necessary to remove the whole valve from the pipeline, which is very suitable for the occasion where the valve and the pipeline are welded together. The flow direction of the medium has changed when it passes through this kind of valve, so the flow resistance of the stop valve is higher than that of other valves.
The commonly used globe valves are as follows: 1) Angle globe valves; In the angle stop valve, the fluid only needs to change direction once, so that the pressure drop through this valve is smaller than that of the conventional stop valve. 2) DC stop valve; In a direct-flow or Y-shaped globe valve, the flow passage of the valve body forms a diagonal line with the main flow passage, so that the damage degree of the flow state is smaller than that of a conventional globe valve, and the pressure loss through the valve is correspondingly smaller. 3) Plunger globe valve: This type of globe valve is a variant of the conventional globe valve. In this valve, the disc and seat are usually designed based on the plunger principle. The disc is polished into a plunger connected with the valve stem, and the seal is realized by two elastic sealing rings sleeved on the plunger. The two elastic sealing rings are separated by a collar, and the sealing rings around the plunger are firmly pressed by the load exerted on the bonnet by the bonnet nut. The elastic sealing ring can be replaced and made of various materials. The valve is mainly used for "opening" or "closing", but it is equipped with a special plunger or special collar, and can also be used to adjust the flow.
butterfly valve
the butterfly plate of the butterfly valve is installed in the diameter direction of the pipeline. In the cylindrical channel of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, and the rotation angle is between and 9. When it rotates to 9, the valve is fully opened.
The butterfly valve is simple in structure, small in size and light in weight, and consists of only a few parts. Moreover, it can be quickly opened and closed only by rotating 9 degrees, and the operation is simple. At the same time, the valve has good fluid control characteristics. When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the only resistance when the medium flows through the valve body, so the pressure drop generated by the valve is very small, so it has good flow control characteristics. Butterfly valve has two sealing types: elastic seal and metal seal. Elastic sealing valve, the sealing ring can be embedded in the valve body or attached to the periphery of the butterfly plate.
The valve with metal seal is generally longer than the valve with elastic seal, but it is difficult to completely seal it. Metal seal can adapt to higher working temperature, while elastic seal has the defect of being limited by temperature.
if the butterfly valve is required to be used as flow control, the main thing is to correctly select the size and type of the valve. The structural principle of butterfly valve is especially suitable for making large diameter valves. Butterfly valves are not only widely used in petroleum, gas, chemical industry, water treatment and other general industries, but also used in the cooling water system of thermal power stations.
there are two kinds of butterfly valves commonly used: wafer butterfly valve and flange butterfly valve. The wafer butterfly valve connects the valve between two pipeline flanges with stud bolts. The flange butterfly valve has flanges on the valve, and the two flanges on the valve are connected to the pipeline flanges with bolts.
ball valve
the ball valve is evolved from the plug valve. It has the same rotating 9-degree lifting action, but the difference is that the cock body is a sphere with a circular through hole or channel passing through its axis. The ratio of spherical surface to channel opening should be such that when the ball rotates 9 degrees, all spherical surfaces should appear at the inlet and outlet, thus cutting off the flow.
The ball valve can be closed tightly with only 9-degree rotation and a small torque. The completely equal inner cavity of the valve body provides a direct flow channel with little resistance for the medium. Generally speaking, the ball valve is most suitable for direct opening and closing, but the recent development has designed the ball valve to make it have the function of throttling and controlling flow. The main feature of ball valve is its compact structure and easy operation and maintenance. It is suitable for general working media such as water, solvent, acid and natural gas, and also for media with bad working conditions, such as oxygen, hydrogen peroxide, methane and ethylene. Ball valve body can be integral or combined.
select the valve to prevent the medium from flowing back
the function of this type of valve is to allow the medium to flow in only one direction and prevent the medium from flowing in the other direction. Usually, this kind of valve works automatically. Under the action of fluid pressure flowing in one direction, the disc opens. When the fluid flows in the opposite direction, the fluid pressure and the self-overlapping disc of the disc act on the valve seat, thus cutting off the flow. Among them, the check valve belongs to this type of valve, which includes swing check valve and lifting check valve. Swing check valve has a hinge mechanism, and a disc like a door freely rests on the inclined seat surface. In order to ensure that the disc can reach the proper position of the valve seat surface every time, the disc is designed in the hinge mechanism, so that the disc has enough swing space and makes the disc truly and comprehensively contact with the valve seat. The disc can be made entirely of metal, or it can be inlaid with leather, rubber, or a synthetic covering, depending on the performance requirements. When the swing check valve is fully opened, the fluid pressure is almost unimpeded, so the pressure drop through the valve is relatively small. The disc of the lifting check valve is located on the sealing surface of the upper seat of the valve body. This valve is like a globe valve except that the disc can be lifted freely. The fluid pressure makes the disc lift from the sealing surface of the valve seat, and the medium backflow causes the disc to fall back to the valve seat and cut off the flow. According to the service conditions, the disc can be all-metal structure, or it can be in the form of embedding rubber pad or rubber ring on the disc frame. Like the globe valve, the passage of fluid through the lift check valve is narrow, so the pressure drop through the lift check valve is larger than that of the swing check valve, and the flow of the swing check valve is rarely restricted.
select valves according to the parameters of regulating medium
in the production process, in order to make the parameters such as pressure and flow of medium meet the requirements of technological process, it is necessary to install regulating mechanism to regulate the above parameters. The main working principle of the adjusting mechanism is to adjust the above parameters by changing the flow area between the valve disc and the valve seat. These valves are collectively referred to as control valves, which are divided into self-driven control valves driven by the power of the medium itself, such as pressure reducing valves, pressure stabilizing valves, etc., and those driven by the power ahead (such as electric power, compressed air and hydraulic power) are called other-driven control valves, such as electric control valves, pneumatic control valves and hydraulic control valves.
introduction of elastic metal hard seal butterfly valve
The elastic metal sealing butterfly valve is a national key new product. The high-performance elastic metal sealing butterfly valve adopts a double eccentric and a special inclined cone elliptical sealing structure. It solves the disadvantage that the sealing surface of the traditional eccentric butterfly valve is still in sliding contact and friction at the moment of opening and closing ~ 1, realizes the effect that the sealing surface of the butterfly plate is separated at the moment of opening and sealed at the moment of closing contact, and achieves the purpose of prolonging the service life and achieving the best sealing performance.
use:
used for adjusting and cutting off gas flow in gas pipelines in sulfuric acid industry, such as inlet and outlet of blower in front of furnace, inlet and outlet of relay blower, inlet and outlet of electric demisting series and connecting valve, inlet and outlet of S2 main blower, converter adjustment, inlet and outlet of preheater, etc.
used in sulfur burning, conversion and dry absorption sections of sulfur-based sulphuric acid system, it is the first choice brand of valves used in sulfur-based sulphuric acid plants, and is considered by users as a butterfly valve with good sealing performance, light operation, side corrosion, high temperature resistance, convenient operation, flexibility and safe and reliable use, which has been widely used.
it is also widely used as a regulating and intercepting device on the pipelines of SO2, steam, air, coal gas, ammonia, CO2 gas, oil products, water, brine, alkali liquor, seawater, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid and other media in chemical industry, petrochemical industry, smelting industry, medicine and food industry.
structural features:
① the unique design of three-way eccentricity makes the sealing surfaces have no friction transmission and prolongs the service life of the valve.
② elastic seal is generated by torque.
③ The ingenious wedge design makes the valve have the function of automatic sealing, and the sealing surfaces are compensatory and have zero leakage.
④ small size, light weight, light operation and easy installation.
⑤ Pneumatic and electric devices can be configured according to users' requirements to meet the needs of remote control and program control.
⑥ The replacement parts can be made of various media, and can be lined with anti-corrosion (F46, GXPP, PO, etc.).
⑦ diversification of continuous structure: clamping, flange and butt welding.
introduction and selection of safety valve
an overview
safety valve is an important safety accessory on boilers, pressure vessels and other pressure equipment. The reliability and performance of its action are directly related to the safety of equipment and people, and are closely related to energy saving and environmental protection. However, some users and design departments always choose the wrong model when selecting models. Therefore, this paper analyzes the selection of safety valve.
II. Definition
The so-called safety valve broadly includes a relief valve. From the management rules, it is directly installed on a steam boiler or a class of pressure vessels, and its necessary condition is a valve that must be approved by the technical supervision department. In a narrow sense, it is called a safety valve, and others are generally called relief valves. The safety valve and the relief valve are similar in structure and performance, both of which automatically discharge the internal medium when the opening pressure is exceeded to ensure the safety of the production device. Because of this essential similarity, people often confuse the two when using them. In addition, some production devices also stipulate that either one can be used. Therefore, the differences between them are often overlooked. As a result, there are many problems. If we want to define them clearly, we can understand them according to the definition set forth in the first part of ASME Boiler and Pressure Vessel Code:
(l) Safety Valve is an automatic pressure relief device driven by the static pressure of the medium in front of the valve. It is characterized by full opening action with sudden opening. For gas or steam applications, as shown in Figure 1.
(2) Relief Valve, also known as relief valve, is an automatic pressure relief device driven by the static pressure of the medium in front of the valve. It opens proportionally as the pressure exceeds the opening force. Mainly used in fluid situations. As shown in figure 2.
(3) Safety relief valve, also known as safety relief valve, is an automatic pressure relief device driven by medium pressure. It is suitable for both safety valve and relief valve according to different application occasions. In Japan, for example, there are few clear definitions of safety valve and relief valve. Generally, safety devices used as large energy storage pressure vessels such as boilers are called safety valves, and those installed on pipelines or other facilities are called relief valves. However, according to the Technical Standard for Thermal Power Generation of Japan's Ministry of International Trade and Industry, safety valves, such as boilers, superheaters, reheaters, etc., are designated as an important part of equipment safety guarantee. When the lower side of the pressure reducing valve needs to be connected with boilers and turbines, it is necessary to install a relief valve or a safety valve. In this way, the safety valve is required to be more reliable than the relief valve. In addition, judging from the identification and regulations of safe discharge in the high-pressure gas management rules of the Japanese Ministry of Labor, the rules of the Ministry of Transport and the ship associations at all levels, we call the valves that guarantee the discharge as safety valves, while the valves that do not guarantee the discharge as relief valves. In China, whether it is full-open or micro-open, it is collectively called safety valve.
III. Selection
1. Classification
At present, there are two kinds of safety valves which are produced in large quantities: spring type and rod type. In addition, there are impulse safety valves, pilot safety valves, safety switching valves, safety decompression valves and dead weight safety valves. Spring-type safety valves mainly rely on the force of springs, which are closed and unsealed. Generally, flammable, explosive or toxic media should be closed, and steam or inert gas can be unsealed. There are also spring-type safety valves with and without wrenches. The wrench is mainly used to check the flexibility of the disc, and sometimes it can also be used for manual emergency pressure relief, as shown in Figure 3. Lever-type safety valve mainly depends on the force of lever hammer, but the selection range is often limited because of its huge volume. When the temperature is high, choose a safety valve with radiator.
the main parameter of the safety valve is the displacement, which depends on the diameter of the valve seat and the opening height of the disc. According to the opening height, it can be divided into two types: micro-opening type and full-opening type. Micro-opening means that the opening height of the disc is 1/4 ~ 1/2 of the throat diameter of the valve seat. Full-open type means that the opening height of the disc is 1/4 of the throat diameter of the valve seat.
2. Selection of safety valve
The operating pressure determines the nominal pressure of the safety valve, the operating temperature determines the operating temperature range of the safety valve, the calculated constant pressure value of the safety valve determines the constant pressure range of the spring or lever, then the material and structural type of the safety valve are determined according to the medium used, and the throat diameter of the safety valve is calculated according to the discharge amount of the safety valve. The following are the general rules for the selection of safety valves.
(l) Generally, hot water boilers use unsealed micro-opening safety valves with wrenches.
(2) Generally, steam boilers or steam pipelines use open safety valves with wrenches.
(3) For liquid incompressible media such as water, a closed micro-opening safety valve or a safety relief valve is generally used.
(4) closed full-open safety valves are generally used for high-pressure water supply, such as high-pressure water supply heaters and heat exchangers.
(5) Generally, closed full-open safety valves are used for compressible media such as gas, such as gas storage tanks and gas pipelines.
(6) Class E steam boilers generally use dead weight safety valves.
(7) Pulsed safety valves are generally used for large-caliber, large-displacement and high-pressure systems, such as temperature and pressure reducing devices and power station boilers, as shown in Figure 8.
(8) Built-in safety valves are generally used for train tankers, car tankers, storage tanks, etc. transporting liquefied gas, as shown in Figure 4.
(9) Generally, a hydraulic safety valve is used at the top of the oil tank, which needs to be used in conjunction with the breathing valve.
(1) Generally, a pilot safety valve is used for underground drainage or natural gas pipelines, as shown in Figure 6.
(11) On the liquid-phase reflux pipeline at the outlet of the tank pump of the liquefied petroleum gas station.