In the traditional concept, butterfly valves can only be used in situations with low temperature, low pressure, and low sealing requirements. With the continuous development of modern process technology and material industry, the application range of butterfly valves has far exceeded the past, and can almost replace most traditional valves, widely applicable in various fields of industry. Especially the triple eccentric metal sealed butterfly valve is more eye-catching.
Due to the fact that the closure of a triple eccentric butterfly valve, like a gate valve, is achieved by torque. The greater the torque of valve closure, the better the sealing of the valve seat. Therefore, some people call a triple eccentric butterfly valve a 90 ° rotating gate valve. In the large-scale maintenance of factories, more and more triple eccentric butterfly valves are replacing gate valves. Therefore, some manufacturers of triple eccentric butterfly valves specifically produce a triple eccentric butterfly valve with the same length as the gate valve, and call this triple eccentric metal sealed butterfly valve a triple eccentric gate valve.
Classification of Sealing Principles for Triple Eccentric Metal Sealing Butterfly Valves
If butterfly valves are classified according to eccentricity, that is, based on the position of the valve stem and valve plate, they can be divided into four types. Three eccentric butterfly valves are currently a type of butterfly valve with outstanding performance in industrial pipelines. According to the sealing form, three eccentric butterfly valves belong to the category of hard sealed butterfly valves. Therefore, the triple eccentric butterfly valve has the characteristics of a hard sealed butterfly valve, which is resistant to high temperature, erosion, and has a long service life. Because the triple eccentric butterfly valve directly overlays high-temperature corrosion-resistant alloy material on the surface of the valve seat, it also has the same good sealing performance as a soft sealing butterfly valve. So what is the principle of a three eccentric butterfly valve? What do the three eccentricities of three eccentricities refer to?
The sealing surface of a three eccentric butterfly valve is an inclined conical surface, and the valve seat of the valve body is in contact with the butterfly plate sealing ring. Its working principle is to drive the movement of the butterfly plate by operating the transmission device. During the movement of the butterfly plate, the sealing ring and the valve seat are in full contact, achieving sealing due to elastic deformation.
A prominent feature of triple eccentric butterfly valves is that they have changed the sealing structure of the valve, no longer relying on traditional positional sealing, but on torsional sealing. This means that sealing is not achieved by relying on the elastic deformation of the valve seat, but by relying on the pressure of the contact surface between the butterfly plate sealing surface and the valve seat to achieve sealing effect. This effectively solves the problem of large metal valve seat leakage, and because the contact surface pressure is proportional to the medium pressure, So the three eccentric butterfly valve has strong resistance to high pressure and high temperature.
Three Eccentricity Metal Sealing Butterfly Valve Sealing Principle
The first eccentricity: the deviation from the plane of the sealing surface to the centerline of the valve stem;
The second eccentricity: the distance from the centerline of the valve body to the centerline of the valve stem;
The third eccentricity: There is an angle between the centerline of the conical surface where the valve body sealing surface is located and the centerline of the valve body channel.
Sealing principle of triple eccentric metal sealing butterfly valve
1.1 Center to center butterfly valve
This type of valve plate is symmetrically arranged with the valve stem as the center. The valve seat is an elastic valve seat, with a temperature and pressure rating of mostly 150 #; The applicable temperature is generally limited to 120 ° C due to the temperature resistance of the valve seat elastomer material. The sealing performance of the valve is good, reaching ANSI-B104 level 6 or zero leakage; The torque required for opening and closing is relatively high. The structure of this type of valve is generally a single valve stem, usually with a diameter less than 500mm. The elastic valve seat covers the valve body, and the medium does not come into direct contact with the valve body, which has good anti-corrosion performance.
1.2 Single eccentric butterfly valve
This type of valve has an eccentricity between the valve stem and the valve plate in one direction. The seats of single eccentric butterfly valves are mostly made of non-metallic materials with elastic body seats, with a temperature and pressure rating of 150 # and below; The applicable temperature generally does not exceed 120 ° C; The sealing performance of the valve is slightly worse than that of the center to center butterfly valve; The torque required for opening and closing is smaller than that of the center opposed butterfly valve. Single eccentric butterfly valves are generally larger diameter butterfly valves, and the valve stem mostly adopts a two section structure.
1.3 Double eccentric butterfly valve
This type of valve has two directions of eccentricity between the valve stem and valve plate, and the sealing surface of the valve is in a round table shape. Double eccentric butterfly valves, also known as high-performance butterfly valves, have two temperature and pressure levels: 150 # and 300 #; The working temperature depends on the temperature resistance of the valve seat material. There are two types of valve seats: elastic body valve seats and metal valve seats. The sealing level of elastic body valve seats can reach ANSI-B104 level 6 or zero leakage. Metal valve seats are often machined from metal sheets, and the sealing level is generally level 4.
The seat of a fire safety double eccentric butterfly valve is composed of an elastic body seat and a metal sheet seat. Under normal circumstances, it is sealed by an elastic valve seat, which can reach the sixth level sealing of ANSI-B104; During a fire, due to the burning of the elastomer valve seat, it was sealed by a metal valve seat, and the sealing of the valve was reduced to level four of ANSI-B104.
The working principle of the sealing principle of a triple eccentric metal sealed butterfly valve
A typical triple eccentric metal sealed butterfly valve, except for the valve stem and valve plate with two eccentricities, the sealing surface of the valve plate and valve seat is in an inclined circular cone shape (this is the so-called third eccentricity of triple eccentricities). When the valve is closed, the valve plate is pushed forward due to eccentricity, and there is no friction between the valve plate and the valve seat during the closing process. The valve plate is directly pressed onto the valve seat, ensuring the service life of the valve; In addition, due to the certain elasticity of the sealing ring of this valve (whether installed on the valve seat or valve plate), and the small gap between the protrusion inside the elastic ring and the elastic ring, the elastic ring can be slightly displaced; When the valve is closed, the elastic sealing ring can automatically move to a position with uniform force under the action of the closing force; In addition, with a small amount of deformation of the elastic ring, the sealing ring at the valve seat is evenly stressed, achieving a sealed state.
Performance changes of butterfly valves with different eccentric structures
As the eccentricity of the valve plate increases and the thickness of the valve plate also thickens, the resistance of fluid flowing through the three eccentric butterfly valve increases; As the eccentricity of the butterfly valve increases, the performance of the valve also undergoes significant changes. From the comparison of four different types of butterfly valves, it can be seen that the three eccentric butterfly valve can generate a significant pressure drop and can be used as a regulating valve; The pressure drop when the fluid flows through the valve increases with the increase of eccentricity; But compared to some other non butterfly valves, the pressure drop of the triple eccentric butterfly valve is still relatively small. As the eccentricity of the butterfly valve changes, the sealing performance of the valve seat also changes. Some three eccentric butterfly valves have valve seat sealing performance. As the number of eccentrics increases, the torque required for valve opening and closing decreases, so the torque required for opening and closing a triple eccentric butterfly valve is much smaller than other types of butterfly valves. As the eccentricity number changes, the temperature and pressure rating range and applicable temperature range of butterfly valves will also have significant changes. The applicable temperature and pressure rating range of three eccentric butterfly valves is different from other types of butterfly valves.
Advantages of the Sealing Principle of Triple Eccentric Metal Sealing Butterfly Valves
4.1 Good cutting performance
The triple eccentric metal seal butterfly valve uses torque to cut off the valve, so there is sealing performance at the valve seat, which is why some people call it a zero leakage valve. The solid particles or dirt contained in the medium have no significant impact on the cutting performance of the triple eccentric metal seal butterfly valve, as the medium flow rate is high when the valve is close, preventing dirt from accumulating at the valve seat.
4.2 Wide scope of application
The triple eccentric metal seal butterfly valve has a wide temperature and pressure range (-253-815 ° C, and the lined triple eccentric metal seal butterfly valve can withstand higher temperatures). The pressure rating of the triple eccentric metal sealed butterfly valve manufactured by a certain factory ranges from 150 # to 2500 #; The pipe diameter ranges from DN80mm to DN2200mm, which is not achievable by most other structural types of valves.
4.3 Intrinsic Fire Safety
Ordinary fire safety butterfly valves, in the event of a fire, the non-metallic material at the valve seal will be burned or damaged at high temperatures, so the sealing performance of this valve will change before and after the fire. Triple eccentric metal sealing butterfly valve, also known as intrinsic fire safety, has no change in its sealing performance before and after a fire due to the absence of non-metallic objects on the sealing surfaces of the valve seat and valve plate.
4.4 Long service life
Triple eccentric metal sealed butterfly valve is a metal to metal sealed valve that has no PTFE, rubber, or other non-metallic materials on the sealing surface. Therefore, it can ensure that the valve is wear-resistant, does not deform during long-term operation, and does not cause valve leakage due to seat deformation. During the opening and closing process of the triple eccentric metal seal butterfly valve, the valve plate and valve seat immediately detach, and there is no friction between them. Therefore, the triple eccentric metal sealed butterfly valve has a long service life, is not prone to leakage, consumes less spare parts, and has low maintenance costs.
4.5 Good regulation performance
Triple eccentric butterfly valves have certain regulating performance and are often used as regulating valves.
4.6 Small size, light weight
Compared with other valves of the same caliber and pressure class, the triple eccentric metal seal butterfly valve has much smaller size and lighter weight, making it cheaper. Additionally, the valve is easy to arrange and the pipeline support is simple. The height, length, and weight of the three eccentric hard seal butterfly valve connected by 150 # DN600mm flange are 1088mm, 267mm, and 425kg, respectively; The length, height, and weight of the same 150 # DN600mm flange connected gate valve are 3300mm, 508mm, and 970kg, respectively.
4.7 Multiple deformation designs
Three eccentric metal seal butterfly valves have various deformation designs to meet the different needs of industrial production, such as: three eccentric metal seal butterfly valves with jackets designed to maintain high temperature, three eccentric metal seal butterfly valves with lining designed for ultra-high temperature, and ultra-low temperature valves with heat dissipation fins manufactured for ultra-low temperature applications, Specially designed triple eccentric metal sealed butterfly valves with steam blowing for the outlet of the ethylene cracking furnace. There are various connection methods for triple eccentric metal sealed butterfly valves, such as clamps, lugs, flanges, and welding.
4.8 There are various valve materials available
Triple eccentric metal sealed butterfly valves can be made of various materials such as carbon steel, low-temperature carbon steel, stainless steel, Monel alloy, Hastelloy alloy, and titanium zirconium two-phase alloy to meet various requirements of the process.
4.9 Easy to automatically control
90 ° rotation opening and closing is an inherent characteristic of butterfly valves. The structure of the 90 ° rotation actuator is simpler than the linear walking structure, and its action process is much faster, which can meet the requirements of rapid opening and closing of valves in industry. At the same time, due to the small operating torque required for the opening and closing of triple eccentric metal sealed butterfly valves, the size of the actuator equipped with butterfly valves is smaller than that of other valves. In addition, butterfly valves are easy to equip with automatic control actuators, creating conditions for automation.
4.10 High valve coefficient
Compared with other valves, the valve coefficient Kv of a three eccentric butterfly valve with the same diameter is much larger than that of a globe valve. Under the same hydraulic conditions, when using a three eccentric butterfly valve, due to its smaller pressure drop, the diameter can be smaller than other valves.
Sealing Principle of Triple Eccentric Metal Sealing Butterfly Valve
This utility model discloses a three eccentric hard sealing butterfly valve, which includes a butterfly valve body, which is a hollow cylindrical structure. The internal movable sleeve of the butterfly valve body is connected to a disc type valve body, and the valve body is fixedly connected to a first rotating shaft that is movably sleeved with the butterfly valve body along its diameter direction. An auxiliary shaft that is coaxial with the first rotating shaft is installed directly below the first rotating shaft, and the internal movable sleeve of the first rotating shaft is connected to a second rotating shaft that is movably sleeved with the auxiliary shaft, A fixed sleeve is installed between the first rotating shaft and the auxiliary shaft, which is fixedly connected to the valve body. On both sides of the fixed sleeve, connecting pieces are symmetrically installed, which are fixedly connected to the first rotating shaft and the auxiliary shaft. One end of the second rotating shaft that extends into the fixed sleeve is fixedly sleeved with a bevel gear, and one side of the bevel gear is meshed with a driven gear. This utility model uses a sealing ring set on the outer ring of the valve body for traditional first sealing, Then, a push plate and retaining ring were used to perform secondary sealing on one side of the valve body, improving the sealing effect and performance of the butterfly valve
