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Leakage and Treatment of Control Valves
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Author:Alliance
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Published time: 2019-12-30
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The leakage of the control valve is generally caused by the leakage in the valve, the leakage of the packing, and the leakage caused by the deformation of the valve core and the valve seat.
The leakage of the control valve is generally caused by the leakage in the valve, the leakage of the packing, and the leakage caused by the deformation of the valve core and the valve seat.
1.In the Valve Leakage
The length of the valve stem is not suitable, the valve stem of the air-opening valve is too long, and the upward (or downward) distance of the valve stem is insufficient, resulting in a gap between the valve core and the valve seat, which cannot be fully contacted, resulting in incomplete closing and internal leakage. Similarly, the valve stem of a gas shut-off valve is too short, which may cause a gap between the valve core and the valve seat, which cannot be fully contacted, resulting in inadequate closing and internal leakage.
Solution: Shorten (or extend) the valve stem of the control valve to make the length of the control valve appropriate so that it no longer leaks.
2. Packing Leaks
After the packing is filled in the stuffing box, it is subjected to axial pressure through the gland. Due to the plastic deformation of the packing, it generates radial force and comes into close contact with the valve stem, but this contact is not very uniform, some parts are loose, some parts are tighter, and some parts are not in contact at all. During the use of the control valve, there is relative movement between the valve stem and the packing. This movement is called axial movement. In the process of use, with the influence of high temperature, high pressure and strong permeability of the fluid medium, the valve stuffing box is also the place where more leakage occurs. The main cause of filler leakage is interface leakage, and there is also leakage for textile fillers (the pressure medium leaks outward along the tiny gaps between the filler fibers). The interface leakage between the valve stem and the packing is caused by the gradual attenuation of the packing contact pressure and the aging of the packing itself. At this time, the pressure medium will leak outward along the contact gap between the packing and the valve stem.
In order to facilitate packing, chamfering at the top of the stuffing box and placing a metal protection ring with small anti-erosion clearance at the bottom of the stuffing box should be convenient. Note that the contact surface between the protection ring and the packing should not be inclined to prevent the packing from being pushed out by medium pressure. The surface of the stuffing box contacting the packing should be finished to improve the surface finish and reduce the wear of the packing. Flexible graphite is used as the filler because it has good air tightness, low friction, small change in long-term use, small wear and tear, and easy maintenance, and the friction force does not change after the gland bolt is re-tightened, the pressure resistance and heat resistance are good, it is not affected by the internal medium, and the metal in contact with the valve stem and the stuffing box is not subject to electrical corrosion or corrosion. In this way, the seal of the valve stuffing box is effectively protected, the reliability of the packing seal is ensured, and the service life is greatly improved.
3. Valve Core and Valve Seat Deformation Leakage
The main reason for valve core and valve seat leakage is due to the strengthening of corrosion caused by casting or forging defects in the production process of the control valve. The passage of the corrosive medium and the flushing of the fluid medium will also cause the leakage of the control valve. Corrosion mainly exists in the form of erosion or cavitation. When the corrosive medium passes through the control valve, it will cause erosion and impact on the material of the valve core and the valve seat, so that the valve core and the valve seat are oval or other shapes. Over time, the valve core and valve seat are not matched, and the gap is not tight enough to cause leakage.
Select corrosion-resistant materials and resolutely remove products with defects such as pits and trachoma. If the deformation of the valve core and valve seat is not too serious, it can be ground with fine sandpaper to eliminate traces and improve the sealing finish to improve the sealing performance. If the damage is severe, the valve should be replaced again.
1.In the Valve Leakage
The length of the valve stem is not suitable, the valve stem of the air-opening valve is too long, and the upward (or downward) distance of the valve stem is insufficient, resulting in a gap between the valve core and the valve seat, which cannot be fully contacted, resulting in incomplete closing and internal leakage. Similarly, the valve stem of a gas shut-off valve is too short, which may cause a gap between the valve core and the valve seat, which cannot be fully contacted, resulting in inadequate closing and internal leakage.
Solution: Shorten (or extend) the valve stem of the control valve to make the length of the control valve appropriate so that it no longer leaks.
2. Packing Leaks
After the packing is filled in the stuffing box, it is subjected to axial pressure through the gland. Due to the plastic deformation of the packing, it generates radial force and comes into close contact with the valve stem, but this contact is not very uniform, some parts are loose, some parts are tighter, and some parts are not in contact at all. During the use of the control valve, there is relative movement between the valve stem and the packing. This movement is called axial movement. In the process of use, with the influence of high temperature, high pressure and strong permeability of the fluid medium, the valve stuffing box is also the place where more leakage occurs. The main cause of filler leakage is interface leakage, and there is also leakage for textile fillers (the pressure medium leaks outward along the tiny gaps between the filler fibers). The interface leakage between the valve stem and the packing is caused by the gradual attenuation of the packing contact pressure and the aging of the packing itself. At this time, the pressure medium will leak outward along the contact gap between the packing and the valve stem.
In order to facilitate packing, chamfering at the top of the stuffing box and placing a metal protection ring with small anti-erosion clearance at the bottom of the stuffing box should be convenient. Note that the contact surface between the protection ring and the packing should not be inclined to prevent the packing from being pushed out by medium pressure. The surface of the stuffing box contacting the packing should be finished to improve the surface finish and reduce the wear of the packing. Flexible graphite is used as the filler because it has good air tightness, low friction, small change in long-term use, small wear and tear, and easy maintenance, and the friction force does not change after the gland bolt is re-tightened, the pressure resistance and heat resistance are good, it is not affected by the internal medium, and the metal in contact with the valve stem and the stuffing box is not subject to electrical corrosion or corrosion. In this way, the seal of the valve stuffing box is effectively protected, the reliability of the packing seal is ensured, and the service life is greatly improved.
3. Valve Core and Valve Seat Deformation Leakage
The main reason for valve core and valve seat leakage is due to the strengthening of corrosion caused by casting or forging defects in the production process of the control valve. The passage of the corrosive medium and the flushing of the fluid medium will also cause the leakage of the control valve. Corrosion mainly exists in the form of erosion or cavitation. When the corrosive medium passes through the control valve, it will cause erosion and impact on the material of the valve core and the valve seat, so that the valve core and the valve seat are oval or other shapes. Over time, the valve core and valve seat are not matched, and the gap is not tight enough to cause leakage.
Select corrosion-resistant materials and resolutely remove products with defects such as pits and trachoma. If the deformation of the valve core and valve seat is not too serious, it can be ground with fine sandpaper to eliminate traces and improve the sealing finish to improve the sealing performance. If the damage is severe, the valve should be replaced again.
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