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The globe valve is widely used. Its valve stem thread is external to the body and comes into direct contact with the medium to prevent corrosion of the valve stem thread by the medium and also to facilitate lubrication and labor-saving operation, as in Figure 3-200.
The stem thread of this globe valve is not lubricated and is medium eroded because it is located inside the valve body where it contacts the medium directly, as shown in Figure 3-201. Shut-off valves of this kind are commonly used in places with relatively small nominal sizes and low to medium operating temperatures for the medium.
The medium's inlet and outlet channels are 180° opposed, similarly directed as illustrated in Figures 3-200 and 3-201. This type of globe valve decreases the amount of harm to the flow condition with a corresponding decrease in pressure loss via the valve.
The inlet and outlet channels of the shut-off valve are not in the same direction but make a right angle of 90 °, as shown in Figure 3-202. This form of shut-off valve changes the flow direction; that is, the medium passing through is forced along a new course that results in some pressure drop. The angle globe valve has its most significant advantage in being fitted at pipeline system corners during installation, saving not only 90 ° elbows but also easing operations. This kind of valve finds wide application in systems for producing synthetic ammonia and the refrigeration system at fertilizer plants.
A shut-off valve with three channels. Usually used to change the direction of medium flow and distribute the medium, as shown in Figure 3-203.
A globe valve has the channel, and the stem with a certain angle between them certain also exist between the sealing surface of the valve seat and the inlet and outlet channels. The valve body can be made as a whole or as a component as shown in Figure 3-204. The split type globe valve uses two valve bodies to clamp the middle of the valve seat. This is convenient for manufacturing and maintenance. This type of shut-off valves ensures that with almost unchanged flow direction of fluid this through it has smallest flow resistance among shut off valves. Its installation method is similar to through type but special attention should be paid to making after pipeline installation easy to operate.
Plunger type globe valve is a deformation of the conventional globe valve. In a plunger valve, the valve disc and seat are designed according to the principle of a plunger. Design the valve disc as a plunger and the valve seat as a sleeve ring, achieving sealing through the combination of the plunger and sleeve ring. The manufacturing process of this valve is simple and the sleeve can be made of flexible graphite or polytetrafluoroethylene, having good sealing performance that can be utilized in high and low-temperature media. This valve is used primarily for opening or closing. Nevertheless, plungers and collars designed in special shapes can also be used for flow regulation. The disadvantage with this type of valve is its slow opening and closing speed. As indicated in Figure 3-205.
Needle globe valves are used for precise flow control and are usually limited to small diameters. Generally, the diameter of the valve seat hole is smaller than the nominal size, as shown in Figure 3-206.
Mainly suitable for high-temperature and high-pressure pipeline systems, the higher the pressure in the valve body cavity, the better the sealing performance of the valve cover, as shown in Figure 3-207.
The valve body and valve cover of this globe valve are threaded and then sealed by welding. Ensure that there is no external leakage at the connection between the valve body and valve cover. This structure is commonly used in forged steel valves with API602, CL800, CL1500, and nominal sizes of DN15~DN50, mainly in the petrochemical and power industries, as shown in Figure 3-208.
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1) Non-metallic sealing material globe valve. Soft sealed shut-off valves Hard sealed shut-off valves.
2) Metal sealing material globe valve
1) Flat Sealing The valve body sealing surface and the valve disc sealing surface are both flat surfaces. This type of sealing is easy to machine, with a simple manufacturing process.
2) Cone sealing. The sealing pairs of both the valve body and the valve disc are designed in cone shapes. This type of seal is easy to work with and quite reliable because impurities in the medium are unlikely to fall onto the sealing surface.
3) Spherical sealing. The sealing surface of the valve body is machined into a very small cone surface, while the valve disc is characterized by a great sphere with high hardness but which allows some rotation flexibility. This pair of sealings is adapted to high temperatures and high pression situations: Sealing is labor-saving plus reliable and has long service life. This form of sealing is only suitable for smaller-diameter valves.
1) Vacuum shut-off valve: shut-off valve for working pressures below atmospheric.
2) Low-pressure globe valve: PN≤16 or Class≤150 globe valve.
3) Medium-pressure globe valve: PN25~PN63 or CL150~CL400 globe valves.
4) High-pressure globe valve: PN100~PN800 or CL600~CL4500 globe valves.
5) Ultra high pressure shut-off valve: any shut-off valve with a nominal pressure equal to or greater than PN1000.
1) High-temperature globe valve: Globe valve t > 450 ℃.
2) Medium-temperature globe valve: 120 ℃< t ≤ 450 ℃ globe valve.
3) Normal temperature stop valve: stop valve.
4) Low-temperature globe valve: -100 ℃< t ≤ -29 ℃ globe valve.
5) Ultra-low temperature globe valve: t ≤ -100 ℃ globe valve.
1) Globe Valve with Flanged Ends
2) Stop Valve with Female Threads
3) Globe Valve with External Threads
4) Welding Stop Valve
5) Stop Valve with Flange Clamp
6) Stop Valve Insert Sleeve
According to the different materials of the sealing pair of the globe valve, both metal and non-metal seals can be used for the globe valve. When using metal seals and non-metallic ceramic seals, not only does it require a higher sealing ratio, but it also requires uniformity around the edges to achieve the desired sealing performance. According to the above requirements, there are various structural designs for sealing pairs, and their sealing principles and calculation of sealing force are also different.
(1) The advantage of flat sealing is that there is no friction when the contact surface is tightly sealed, so the guidance requirements for the closing part are not important, and the requirements for the scratch resistance of the sealing surface material are not strict. Meanwhile, when the roundness of the sealing surface is deformed due to pipeline stress, it will not affect the sealing performance of the sealing surface. The disadvantage is that solid particles and precipitates in the medium can easily damage the sealing surface. The sealing principle is that when the medium flows in from below the valve disc, the applied sealing force must be equal to or greater than the sum of the necessary specific pressure generated on the sealing surface and the upward force of the medium
FMz - total force applied to the sealing surface;
FMF - Sealing force on the sealing surface;
FMU - the medium force on the sealing surface;
DMN - Inner diameter of sealing surface;
Bm - sealing surface width;
QMF - The sealing surface must have a specific pressure;
P - Calculate pressure, usually taking the nominal pressure.
When the medium flows in from above the valve disc, the applied sealing force is equal to or greater than the difference between the required specific pressure generated on the sealing surface and the acting force of the medium
(2) Cone sealing makes the sealing surface conical, narrowing the contact surface. Under a certain sealing force, this type of seal greatly increases its sealing pressure, making it easy to achieve sealing. Compared to flat sealing, the applied sealing force is smaller while ensuring sealing. Due to the narrow sealing surface, it is difficult for the valve disc to fall correctly on the valve seat. In order to achieve the best sealing performance, it is necessary to guide the valve disc. After guiding the valve disc, good sealing performance can be achieved. When the valve disc is guided in the valve body, the lateral thrust of the flowing medium on the valve disc is borne by the valve body, rather than by the valve stem, which further enhances the sealing performance and reliability of the packing seal. On the other hand, conical seals are matched under friction, so the sealing material must be resistant to scratches. Compared with flat seals, conical seals are less susceptible to damage from solid particles and media precipitates, but they are also not suitable for use in media containing solid particles and media precipitates. This type of seal is mainly used in media without particles. The sealing principle is that when the medium flows under the valve disc, the applied sealing force must be equal to or slightly greater than the sum of the required specific pressure generated on the sealing surface and the upward force of the medium, as shown in Figure 3-210 and shown in equations (3-5) to (3-7).
In the formula, FMz - the total force applied to the sealing surface;
FMF - Sealing force on the sealing surface;
FMJ - Medium force on the sealing surface;
DMW - Outer diameter of sealing surface;
DMN - Inner diameter of sealing surface;
Fm ⁻ - friction coefficient of sealing surface;
α---- Sealing surface cone half angle;
QmF ⁻ - The sealing surface must have a specific pressure;
BM - sealing surface width;
P - Calculate the pressure, usually taking the nominal pressure.
When the medium flows in from above the valve disc, the applied sealing force is equal to or greater than the difference between the required specific pressure generated on the sealing surface and the acting force of the medium, as shown in Figure 3-210.
In order to improve the strength of the conical seal without sacrificing its sealing stress, the half angle of the sealing surface cone is made to 15 °, which provides a wider sealing surface and makes it easier for the valve disc to seal with the valve seat. In order to achieve higher sealing stress, the sealing surface of the valve seat begins to come into contact with the valve disc, with a narrower part of about 3mm, and the remaining tapered part can be slightly longer. When the sealing load increases, the degree of sliding of the valve disc into the valve seat deepens, thereby increasing the width of the sealing surface. This sealing surface design is not as susceptible to erosion and damage as narrow sealing surfaces. In addition, due to the longer conical surface, the throttling characteristics of the valve are improved.
(3) The spherical seal is shown in Figure 3-211, with the valve disc made spherical and the valve seat made conical. The ball of the valve disc can rotate freely in the hole of the valve stem. Therefore, the valve disc can be adjusted by rotating within a certain range on the valve seat. Due to the fact that the contact between the two sealing surfaces is almost on the same line, which is a line seal, the sealing stress is high and it is easy to seal. Due to the fact that the valve disc sphere can be made of hard alloy or ceramic materials, with a hardness of 40-60HRC and the ability to withstand high temperatures. Therefore, it can be used as a high-temperature shut-off valve. The disadvantage is that the linear contact of the sealing surface is prone to erosion and damage. So the valve seat should be made of corrosion-resistant materials. Spherical sealed globe valves are suitable for gases or liquids with small solid particles in the medium. The sealing principle is that when the medium flows under the valve disc, the applied sealing force must be equal to or slightly greater than the sum of the required specific pressure generated on the sealing surface and the upward force of the medium.
FMz - total force applied to the sealing surface;
FMF - sealing force on the sealing surface;
FMJ - Medium force on the sealing surface;
DMN - Inner diameter of sealing surface;
QMF - The sealing surface must have a specific pressure;
P - Calculate pressure, usually taking the nominal pressure.
When the medium flows in from above the valve disc, the applied sealing force must be equal to or slightly greater than the difference between the specific pressure generated on the sealing surface and the downward force of the medium. As shown in Figure 3-211.
(4) The radial seal is shown in Figure 3-204. Radial sealing refers to the sealing of a plunger type globe valve, and its sealing principle is that in a plunger valve, the valve disc and valve seat are designed according to the principle of the plunger. Design the valve disc as a plunger, and the valve seat as a sleeve ring. The material of the sleeve ring can be flexible graphite or polytetrafluoroethylene. The valve seat is composed of an upper sleeve ring, an isolation ring, and a lower sleeve ring, which are compressed with a valve cover. Sealing is achieved through the tight fit between the plunger and the sleeve ring.
The application of globe valves is very extensive, and globe valves are used in many situations. However, depending on the different structural types of globe valves, they are also suitable for different occasions.
(1) Needle shaped globe valves are used for precise flow control. The valve disc is usually integrated with the valve stem, and it has a needle shaped head that fits well with the valve seat and has very high accuracy. Moreover, the thread pitch of the needle shaped globe valve stem is finer than that of the valve stem thread of a general globe valve. Under normal circumstances, the size of the valve seat hole for needle shaped globe valves is smaller than the size of the pipeline. Therefore, it is usually limited to use in pipelines with smaller nominal diameters and is more commonly used for sampling valves.
(2) The valve stem and channel of the DC stop valve form a certain angle, and the sealing surface of the valve seat also has a certain angle with the inlet and outlet channels. The valve body can be made into a whole or separate type. The split valve body globe valve uses two valve bodies to clamp the valve seat in the middle for easy maintenance. This type of shut-off valve ensures that the flow direction of the fluid remains almost unchanged, and the flow resistance is minimized in the shut-off valve. The sealing surfaces of the valve seat and disc can be welded with hard alloy, making the entire valve more resistant to erosion and corrosion. It is very suitable for pipeline control in alumina production processes, as well as in pipelines with coking and solid particles.
(3) The biggest advantage of angle globe valve is that it can be installed at the corners of the pipeline system, which not only saves 90 ° elbows but also facilitates operation. Therefore, this type of valve is most suitable for use in the synthetic ammonia production system and refrigeration system of fertilizer plants. J44H-160, J44H-320, L44H-160, and I44H-320 are completely designed for synthetic ammonia production systems.
(4) The structural characteristics of this valve are that the valve body is divided into connected and split types, and the valve disc is made of STL hard alloy steel balls or ceramic balls made of amorphous materials through powder forming, high-temperature sintering, and precision grinding. The lower end of the valve stem is rolled to wrap the ball inside the valve stem ball hole. When the ball rotates in three dimensions inside the valve stem ball hole, it can generate countless sealing lines, greatly increasing the service life of the sealing surface and ensuring reliable sealing. Due to the limitation of spherical sealing, this valve is generally used for smaller nominal sizes, approximately DN6~DN25. This valve is suitable for high-temperature and high-pressure steam pipelines in nuclear power plants and thermal power plants, instrument pipelines in sampling and sewage systems, as well as temperature resistant, pressure resistant, wear-resistant, and corrosion-resistant pipelines in petrochemical and chemical systems.
(5) The structural characteristics of the cut-off valve for high-temperature and high-pressure power plants are that the connection between the valve body and the valve cover is pressure self tightening sealing or clamp type, and the connection between the valve body and the pipeline is butt welding. The valve body material is mostly chromium molybdenum steel or chromium molybdenum vanadium steel, and the sealing surface is mostly welded with hard alloy. Therefore, this type of valve is resistant to high temperature and pressure, and has good heat resistance; The sealing surface is wear-resistant, scratch resistant, and corrosion-resistant, with good sealing performance and long service life. Most suitable for pipelines of high-temperature and high-pressure water, steam, oil products, and superheated steam in thermal power industrial systems, petrochemical systems, and metallurgical industries.
(6) API globe valves are designed strictly in accordance with API 623-2015 and ASME B16.34; The connection between the valve body and the valve cover, the installation of the packing box, the valve stem nut, and the upper seal are all strictly designed in accordance with API 623. The valve material selection fully meets the requirements of API 623. The structural length complies with ASME B16.10; The flange connection size shall comply with ASME B16.5. The inspection and testing of valves shall be strictly carried out in accordance with API598. Therefore, this valve is widely used in petrochemical pipelines and is also applicable in systems such as power, metallurgy, and textiles.
(7) The cut-off valve for oxygen pipelines is designed strictly according to the requirements of oxygen pipelines. The packing box is strictly sealed, and external dirt must not enter the packing box. The flanges at both ends of the valve body are equipped with grounding devices. After installation on the pipeline, they should be grounded to prevent static electricity and fire. The shell material of this valve is austenitic stainless steel or copper, which has good conductivity and is not prone to static electricity ignition. The sealing material is polytetrachloroethylene for the valve body material, which is a soft seal with good sealing performance and zero gas leakage during gas inspection. The valve is strictly degreased with carbon tetrachloride before assembly, and there is absolutely no grease or dirt, which will not cause static electricity and fire. This valve is suitable for oxygen pipelines in metallurgical systems and is also applicable to oxygen pipelines in other industries.
(8) The petroleum liquefied gas shut-off valve is designed specifically for pipelines or devices of petroleum liquefied gas, and its structure pays attention to fire protection requirements. The filler is made of polytetrafluoroethylene, with reliable sealing and absolutely no external leakage. The sealing auxiliary material adopts polytetrafluoroethylene or nylon as the material for the valve body, which is a soft seal and reliable sealing. This valve is suitable for liquefied petroleum gas pipeline systems as an opening and closing device, as well as other pipelines with a temperature ≤ 80 ℃.
(9) The stem of this type of globe valve does not come into direct contact with the working medium. Suitable for different working conditions depending on the material of the shell, sealing pair, packing, and valve stem. If the valve body and cover material is carbon steel, the sealing material is alloy steel, the packing is flexible graphite, and the valve stem material is Cr13 series stainless steel, it is suitable for water, steam, and oil pipelines; If the material of the valve body and cover is 12Cr18Ni9 or 06Cr19Ni10, the sealing material is the valve body itself or hard alloy, the packing is polytetrafluoroethylene, and the valve stem material is 14Cr17Ni2, it is suitable for corrosive media pipelines or devices based on nitric acid; If the material of the valve body and valve cover is 06Cr17Ni12Mo2Ti, the sealing material is the valve body itself or hard alloy, the packing is polytetrafluoroethylene, and the valve stem material is 14Cr18Ni11Si4AlTi, it is suitable for corrosive media pipelines or devices based on acetic acid. However, the maximum nominal size of this type of globe valve is DN200. Globe valves above DN200 should be equipped with a bypass valve or an internal bypass structure should be designed. Generally, the inlet end of globe valves with a diameter of ≥ DN200 is above the valve disc, that is, high inlet and low outlet. This is to prevent excessive force during closing and the valve stem from being too thick.
(10) The stem thread of this type of globe valve is directly in contact with the working medium, and is directly corroded by the medium, making the stem thread prone to corrosion and causing difficulty in opening and closing. This type of shut-off valve has a relatively small nominal size, generally between DN6 and DN50, and is mostly used in instrument valves and sampling valves.
(11) API 602 Forged Steel Globe Valve This type of globe valve is designed according to the American Petroleum Institute standard API 602. The valve body and valve cover are forged from carbon steel or stainless steel, and the valve body and valve cover are connected by bolts, threads, and welding. There are upper threaded valve stem and lower threaded valve stem. The sealing material is Cr13 steel, stainless acid resistant steel, and STL hard alloy. The packing is flexible graphite or polytetrafluoroethylene. The connection methods include flange, thread, socket welding, and butt welding. The pressure rating is CL800~CL1500, and the nominal size is NPS%~NPS2 ½。 Widely used in equipment and pipelines in petrochemical, power, chemical and other sectors, the working medium is steam, oil, and corrosive medium. The structural length shall comply with ASME B16.10, the flange connection size shall comply with ASME B16.5, the welding end size shall comply with ASME B16.25, the socket welding hole size shall comply with ASME B16.11, and the threaded connection end size shall comply with ASME B1.20.1.
(12) Plunger stop valve: This type of plunger valve belongs to radial sealing, which is achieved by two elastic sealing rings nested on the polished plunger. Two elastic sealing rings are separated by a sleeve ring, and the load applied to the valve cover through the connecting bolts of the valve body and valve cover presses the elastic sealing ring around the plunger firmly to ensure sealing. The material combination of this valve is carbon steel for the shell, Crl3 stainless steel for the plunger, and flexible graphite for the sealing ring, which can be used in pipelines for water, steam, and oil; If the shell is made of stainless acid resistant steel, the plunger is made of stainless acid resistant steel, and the sealing ring is made of polytetrafluoroethylene, it is suitable for acidic and alkaline corrosive media. The advantages of this valve are reliable sealing, long service life, and easy maintenance; The disadvantage is slow opening and closing speed. This type of valve is widely used in urban construction systems and water and steam pipelines in urban heating.
Globe valves are one of the most widely used valve types. With the development of ball valves and butterfly valves, some of the applications of globe valves have been replaced. However, from the characteristics of globe valves themselves, they cannot be replaced. The selection principles are:
1) Globe valves should be selected on pipelines or devices with high temperature and high pressure media. It is advisable to use globe valves on high-temperature and high-pressure pipelines in petrochemical systems such as thermal power plants, nuclear power plants, and petrochemical systems.
2) On pipelines with less strict requirements for flow resistance. That is, places where pressure loss is not considered much.
3) Small valves can choose globe valves, such as needle valves, instrument valves, sampling valves, pressure gauge valves, etc.
4) There is flow regulation or pressure regulation, but the precision requirement for regulation is not high, and the diameter of the pipeline is relatively small. For example, on pipelines with a nominal size ≤ 50mm, it is advisable to use a globe valve or a throttle valve.
5) Small and large fertilizers in the production of synthetic ammonia industry should use high-pressure angle globe valves or high-pressure angle throttle valves with nominal pressures of PN160 or PN320.
6) In the desilication workshop and pipelines prone to coking during the production of alumina by Bayer process, it is advisable to use a separate valve body with removable valve seats
DC stop valve or DC throttle valve with hard alloy sealing pair.
7) In the water supply and heating engineering of urban construction, for pipelines with smaller nominal sizes, globe valves, balance valves, or plunger valves can be used, such as on pipelines with nominal sizes less than DN150.
