What are the common faults of valves?

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This post was last edited by Qingse Nianhua on 2017-9-5 at 20:33. Common faults of valves and their solutions. I. Common situations of valve leakage and corresponding solutions. 1. Leakage in the valve body. 1.1 Causes: 1.1.1 The valve body has sand holes or cracks. 1.2.2 The valve body is cracked due to welding repairs. 1.2 Solutions: 1.2.1 Polish the area where cracks are suspected, then treat it with a 4% nitric acid solution; cracks will become visible if they exist. 1.2.2 Repair the cracked areas by filling them in. 2. Damage to the valve stem and its associated threads, or breakage or bending of the valve stem head. 2.1 Causes: 2.2.1 Improper operation, excessive force used when opening or closing the valve, malfunctioning limit devices, and failure of the torque protection mechanism. 2.2.2 Threads that are either too loose or too tight. 2.2.3 Excessive number of operations and prolonged use. 2.2 Solutions: 2.2.1 Improve the way the valve is operated; do not use excessive force； 8. Check the limit devices and the over-torque protection devices. 2.2.2 Select appropriate materials, and ensure that the assembly tolerances meet the requirements. 2.2.3 Replace worn-out parts. 3. Leakage at the valve cover joint: 3.1 Causes: 3.1.1 Insufficient bolt tension or uneven tightening. 3.1.2 The gaskets are not of suitable quality or are damaged. 3.1.3 Defects in the joint surface. 3.2 Solutions: 3.2.1 Tighten the bolts again or ensure that the gaps between the valve cover flanges are even. 3.2.2 Replace the gaskets. 3.2.3 Disassemble and re-machine the sealing surfaces of the valve cover. 4. Internal leakage in the valve: 4.1 Causes: 4.1.1 Inadequate sealing when closing. 4.1.2 Damage to the joint surfaces. 4.1.3 Excessive gap between the valve core and the valve stem, resulting in the valve core sagging or failing to make proper contact. 4.1.4 Poor-quality sealing materials or sticking of the valve core. 4.2 Solutions: 4.2.1 Improve the operating procedure by opening and closing the valve again. 4.2.2 Disassemble the valve and re-machine the sealing surfaces of the valve core and seat. 4.2.3 Adjust the gap between the valve core and the valve stem or replace the valve disc. 4.4.4 Disassemble the valve to eliminate sticking. 4.4.5 Replace or weld new sealing rings. 5. Separation of the valve core from the valve stem, resulting in malfunctioning operation: 5.1 Causes: 5.1.1 Improper repair work. 5.1.2 Corrosion at the junction between the valve core and the valve stem. 5.1.3 Excessive force applied during operation, causing damage to that junction. 5.1.4 Looseness of the retaining washers for the valve core or wear on the connection areas. 5.2 Solutions: 5.2.1 Pay attention to checking these aspects during maintenance. 5.2.2 Replace the valve stem with a material resistant to corrosion. 5.2.3 Do not apply excessive force when operating the valve, nor try to open it further after it has been fully opened. 5.2.4 Inspect and replace any damaged parts. 6. Cracks in the valve core and seat: 6.1 Causes: 6.1.1 Poor quality of welding at the joint surfaces. 6.1.2 Large temperature differences on either side of the valve. 6.2 Solutions: 6.2.1 Weld the cracked areas, carry out heat treatment as specified, then polish and grind the surfaces. 7. Inability of the valve stem to move up or down or failure to operate properly: 7.1 Causes: 7.1.1 Over-tightening when closing in cold conditions, leading to locking after heating, or over-tightening after full opening. 7.1.2 Excessive compression of the packing. 7.1.3 Too small a gap in the valve stem, resulting in locking. 7.1.4 Excessive tightness in the fit between the valve stem and the nut, or damage to the threads. 7.1.5 Misalignment of the packing gland. 7.1.6 Bent valve stem. 7.1.7 Excessively high medium temperature, poor lubrication, and severe rusting of the valve stem. 7.2 Solutions: 7.2.1 Heat the valve body and then try to open it slowly with force, or open it fully first and then close it slightly. 7.2.2 Loosen the packing gland slightly before attempting to open the valve. 7.2.3 Increase the gap in the valve stem appropriately. 7.2.4 Replace the valve stem and nut. 7.2.5 Readjust the bolts of the packing gland. 7.2.6 Straighten the valve stem or replace it. 7.2.7 Use pure graphite powder as a lubricant for the valve stem. 8. Packing leakage: 8.1 Causes: 8.1.1 Incorrect type of packing used. 8.1.2 The packing gland is not tightened properly or is misaligned. 8.1.3 Incorrect method of installing the packing. 8.1.4 Damage to the surface of the valve stem. 8.2 Solutions: 8.2.1 Select the right type of packing. 8.2.2 Check and adjust the packing gland to prevent misalignment. 8.2.3 Install the packing using the correct method. 8.2.4 Repair or replace the valve stem