Feasibility of replacing gate valve and globe valve with double eccentric hemispherical ball valve
Ball valve is the fastest growing type of valve in China in recent years. In addition to hard-sealed ball valve, double eccentric hemispherical ball valve has also developed rapidly. Double eccentric hemispherical ball valve is a domestic product developed by importing German hemispherical valve products under the premise of carefully weighing the advantages and disadvantages of various valves such as ball valves, butterfly valves, and gate valves. Gate valve, globe valve and ball valve and other similar products can be widely used in petroleum, chemical, electric power and metallurgical industries... The double eccentric hemispherical ball valve has a unique design, novel structure, and the scope of orders is constantly expanding. It has indeed replaced ball valves and butterfly valves in different occasions. , gate valve and other valves, the structural advantages of double eccentric hemispherical ball valve are as follows:
1. The hemispherical ball valve adopts the principle of wedging and eccentricity in the structure.
The center of rotation of the valve body and the valve core (ie the axis of the valve stem) is offset from the geometric center of the sealing spherical surface of the valve core by a radial dimension, and also has an offset dimension from the sealing surface of the valve seat on the axis of the valve body passage. The sealing pair is Under the action of metal-metal external force, the valve relies on two eccentrics to achieve self-locking closure. The reasonable selection of eccentricity makes the self-locking angle smaller than the friction angle. If the self-locking angle is too small, it is easy to close, but difficult to open. Although the opening force is small, the closing torque increases rapidly. It is very important to determine the reasonable eccentricity of the two pairs through repeated experiments on the test bench, and the reliable self-locking performance ensures that they are tightly sealed. This is the core technology of the eccentric hemispherical valve. From the structural principle to achieve the best sealing through manufacturing methods, the ball valve, butterfly valve, gate valve, globe valve, etc. are indeed inferior.
2. The hemispherical valve is easy to realize and maintain zero leakage for a long time.
The sealing between the valve core and the valve seat is in spherical line contact, and self-locking is realized by eccentricity. The sealing pair hardly contacts in the whole process of opening and closing. There are no leaks anywhere. Scale or other deposits on the valve seat, the valve core has the ability to strongly remove the scale in the process of contacting the valve seat. While the sealing surface of the gate valve is in frequent reciprocating motion of opening and closing, the mixed flow medium scales and deposits in the lower cavity of the valve body, the globe valve completely relies on positive pressure to achieve sealing, the scale on the valve seat has no cleaning ability, and the two are packed together. Frequent and repeated wear and tear can easily cause internal leakage and external leakage of gate valves and globe valves. The ball valve seal depends on the valve seat being squeezed on the spherical surface for a long time. It must wear faster than the hemispherical valve. The butterfly valve seal is mediated by rubber, which is far from the metal hard sealing performance of the hemispherical valve, ball valve and gate valve. After long-term use of the hemispherical valve, the valve seat will also have a small amount of wear. It can continue to be used through adjustment. The valve stem and packing only need to rotate 90° during the opening and closing process. A few bolts can achieve no leakage at the packing, while other valves are still barely used for small leakage, and the valve is replaced with a large leakage.
3. Double eccentric hemispherical ball valve is extremely easy to operate.
In the whole process of opening and closing of the double eccentric hemispherical ball valve, the sealing pair is almost in an undamped idling state, the external force is only released or pressed at the moment of opening and closing, and the valve stem only needs to be rotated 90°, which is light and fast, of course, the operation is easy. In the process of opening and closing, the ball valve operates under the holding force of the valve seats at both ends. It has a larger opening and closing torque than the semi-ball valve. The larger the nominal diameter, the more obvious the opening and closing torque difference. The opening and closing of the butterfly valve is to overcome the deformation of the rubber. to achieve, the torque is larger. The gate valve and globe valve operate for a long time and are laborious.
4. The double eccentric hemisphere valve has a long service life.
The sealing pair belongs to bimetal, and the alloys for different purposes are surfacing on the parent body. After special heat treatment, the mechanical properties and physical and chemical indicators of the sealing pair reach the best state to meet different working conditions (strong wear, rapid erosion, severe corrosion and other media. ), the hardness of the valve seat is slightly lower than that of the valve core, and the material and heat treatment process are different. Practice has proved that its anti-corrosion and anti-seize ability is 6 times that of stainless steel sealing pair, and the valve can be opened and closed tens of thousands of times without failure, extending the service life.
5. Double eccentric hemispherical ball valve has a wide range of applications.
Side-mounted eccentric hemispherical valve series are widely used in non-ferrous smelting, gas and natural gas, pulverized coal injection and dust removal of steel, electric power slag transportation, pulverized coal transportation systems, harmful gases (hydrogen sulfide, phosgene, etc.) and oil products ( Heavy oil, crude oil, residual oil, etc.) smelting and transportation. The reason why the hemisphere valve has a wide range of applications is mainly because the sealing pair can be surfacing with different alloys to make it bimetal, and the main parts such as the valve body and the valve stem are made of the required materials to meet the needs of different working conditions.