Globe valve structure, function, principle

The shutoff valve is a forced seal type valve, so when the valve is closed, pressure must be applied to the valve flap to force the seal surface not to leak. When the medium enters the valve from below the valve flap, the resistance to be overcome by the operating force is the friction between the stem and the packing and the thrust generated by the pressure of the medium. The force of the closing valve is greater than the force of the opening valve, so the valve stem The diameter should be large, otherwise there will be stem bending failure. In recent years, after the emergence of the self-sealing valve, the medium flow of the stop valve has been changed from above the valve flap into the valve chamber. At this time, under the pressure of the medium, the force to close the valve is small, and the force to open the valve is large. The diameter can be reduced accordingly. At the same time, this type of valve is also tighter under the influence of the medium. China's valve "three to give" has stipulated that the flow direction of the globe valve shall be adopted from top to bottom. When the closing valve is opened, the valve opening height is 25% to 30% of the nominal diameter, and the flow rate has reached a large value, indicating that the valve has reached the fully open position. Therefore, the fully open position of the stop valve is determined by the stroke of the valve flap. Valve repair process steps and process principles Valve dismantling 1. Handle a good job ticket and confirm that there is no water or pressure in the piping system before starting work. 2. Prepare special tools and other tools to set up scaffolds and cranes. Point, contact the thermal workers to remove the power cord; 3. Manually open the valve 1-2 button, use the chain, wire rope hoisting the electric mechanism, disassemble the electric mechanism and the bracket, connect the bolt, the electric mechanism to exit smoothly, hang 4. Remove the bolts of the valve indicator slider and take down the flat keys to save it; 5. Rotate the bracket counterclockwise to withdraw and hang it down; 6. Remove the packing gland fastening bolts, remove the packing gland, and dig. Fill out the packing; 7. Using a special tool, rotate the headgear back, pull out the door rod and valve head, and seal the valve port. Valve repair process steps and process principles Valve parts inspection and measurement 1. Valve body maintenance (valve body and outer wall clean without debris. Body without cracks, wear heavy skin and trachoma and other defects.) 2. Valve flap. Seat Sealing surface grinding: According to the valve flap. Valve seat sealing surface defect degree of grinding, such as a small defect can be used to finely grind the grinding machine. If the defect is large, the valve sealing surface can be used lathe turning, the valve seat sealing surface grinding can be used Machine for coarse, medium, fine grinding, pass the tightness test after passing; 3. Inspect the valve stem, there should be no defects such as bending, wear, erosion. Seals with packing should be smooth and free of grooves and other defects. The thread on the valve stem is not damaged, and it fits well with the mother nut and turns freely, otherwise it should be repaired. The stem bending should be within 0.1mm, wear pit depth should not exceed 0.1~0.2mm; 4. Measure the gap between stem and headgear, should be in the range of 0.2 ~ 0.25mm, seat and packing gland The clearance between them should be in the range of 0.2~0.3mm. Inspection and measurement of valve parts 5. Check the connection thread between the bracket and the valve seat. It should be free of damage and well-matched. The fastening bolts should be well matched with the nut; 6. Packing gland, packing room, door rod gap measurement: The gland pressure can not be less than 10% of the packing room and not more than 20%. The stem clearance is 0.10-0.20mm. The gap between the sealing disc, seal ring and self-sealing packing room should be between 0.10-0.20mm. 7. The thread wear degree should not exceed 1/3 of the thread width, and it should be well matched with the valve sleeve. 8. Inspect the wear of the transmission mechanism, the worm gear and the worm. The wear should not exceed 1/3 of the tooth thickness. There should be no cracks and meshing defects in the meshing part. Inspect the bearing for wear and rotation and inflexibility. Manual and automatic switching is flexible and reliable. The transmission performance is good. Valve repair process steps and process principles Hongdan powder test 1. Valve and valve seat sealing surface roughness should be 3.2μm or more; 2. Valve and valve seat sealing surface contact 100%.