Solutions to control valve leakage

Thread Content

This post was last edited by yuchenchf on 2017-3-16 at 15:30. Issue with leakage in the control valve: internal leakage of the valve, and the length of the valve stem is not appropriate. The gas control valve has a too long valve stem; the distance that the valve stem can move upward (or downward) is insufficient, which creates a gap between the valve core and the valve seat. As a result, they cannot make full contact, leading to poor sealing and internal leakage. Similarly, the valve stem of the air shut-off valve is too short, resulting in a gap between the valve core and the valve seat; this prevents proper contact and leads to poor sealing and internal leakage. 　　Solution: The valve stem of the control valve should be shortened (or lengthened) to adjust its length appropriately, so as to eliminate internal leakage. 　　2 Packing leakage. After the packing is inserted into the stuffing box, axial pressure is applied to it via the gland. Due to the plasticity of the filler, a radial force is generated, causing it to make close contact with the valve stem; however, this contact is not very uniform. In some areas, the contact is loose; in other areas, it is tight, and there are even some areas where there is no contact at all. During operation of a control valve, there is relative movement between the valve stem and the packing, and this movement is called axial motion. During operation, due to the effects of high temperature, high pressure, and fluid media with strong permeability, the packing gland of control valves is also a part where leaks occur frequently. The main cause of filler leakage is interfacial leakage; in the case of textile fillers, seepage also occurs (the pressure medium leaks outward through the tiny gaps between the filler fibers). Interfacial leakage between the valve stem and the packing is caused by the gradual decrease in the contact pressure of the packing, as well as aging of the packing itself; under such conditions, the pressurized medium leaks outward through the gap between the packing and the valve stem. 　　Solution: To facilitate the filling of the packing, chamfer the top of the packing box, and place an erosion-resistant metal protective ring with a small clearance at the bottom of the packing box (the contact surface with the packing must not be inclined) to prevent the packing from being pushed out by the medium pressure. The metal surfaces of all parts of the stuffing box that come into contact with the packing must be finely processed to improve surface finish and reduce packing wear. Flexible graphite is chosen as the packing due to its excellent airtightness, low friction, minimal changes over time, low wear and burnout, ease of maintenance, unchanged friction after the gland bolts are retightened, good pressure and heat resistance, immunity to corrosion by internal media, and the fact that it does not cause pitting or corrosion in the metals in contact with the valve stem and the packing box interior. In this way, the sealing of the valve stem stuffing box is effectively protected, ensuring the reliability and durability of the stuffing seal. 　　Leakage due to deformation of the 3 valve spools and seat. The main cause of leakage at the core and valve seat is the enhanced corrosion resulting from casting or forging defects during the production of the control valve. The passage of corrosive media, as well as the scouring by fluid media, can also cause leakage in control valves. Corrosion mainly occurs in the form of erosion or cavitation. When corrosive media pass through the control valve, it causes erosion of the valve stem and seat materials as well as impact that results in these components taking on an oval or other shape. Over time, this leads to a mismatch between the valve stem and seat, creating gaps that prevent proper sealing and result in leaks. 　　Solution: The key is to ensure proper selection and high quality of the materials used for the valve core and valve seat. Choose corrosion-resistant materials, and firmly reject products with defects such as pitting and sand eyes. If the valve core and seat are not severely deformed, they can be polished with fine sandpaper to remove any marks and improve the smoothness of the seal, thereby enhancing its sealing performance. If the damage is severe, a new valve should be replaced. 　　Everyone can add explanations for the incorrect or incomplete parts, so that those who read it next will learn more; you know exactly what everyone needs.