Common valve failures and solutions. Think about, what else are there?

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Common valve failures and repairs: 1. The valve fails to open or close smoothly, is inflexible, or cannot be operated properly; in some cases it is even unable to open or close at all. This is mainly due to obstruction between the valve stem and other components, particularly obstruction between the valve stem and the packing. Common issues include: 1. The packing gland becoming skewed and touching the valve stem – Solution: Install it correctly. 2. Incorrect installation or excessive tightening of the packing – Solution: Pre-tighten the packing and loosen it appropriately. 3. Valve stem seized by the packing gland – Solution: Replace or repair. 4. Seizing or scoring between components – Solution: Lubricate the valve stem properly. II. Scratches on the valve sealing surface, abrasions on the smooth portion of the valve stem, and abrasions on the threaded portion of the valve stem, etc. 1. After grinding the sealing surface, abrasive particles remained embedded in it and were not removed properly, resulting in scratches on the sealing surface ； In some cases, after use, the abrasive particles are washed away by the medium and end up sticking to the sealing surface; this, combined with the opening and closing of the valve, causes abrasion. – Treatment method: Select the appropriate abrasive, and the sealed surface must be cleaned thoroughly after grinding. 2. The debris or welding slag in the medium was not removed thoroughly, resulting in scratches. – Handling method: Clean it thoroughly again. 3. The valve stem rubs against the packing gland and packing gasket; furthermore, media containing boron will crystallize into hard particles upon leakage, which damage the surface of the valve stem during opening and closing operations at the contact surface between the packing and the valve stem. – Treatment method: Proper installation, adjustment of the clearance between components, and increasing the surface hardness of the valve stem. 4. There is dirt and debris on the trapezoidal threads, resulting in poor lubrication conditions; the valve stem and related parts are deformed – Solution: Remove the debris and apply lubricant to high-temperature valves in a timely manner ； Correction of deformed parts. III. Packing leakage and leakage at the connection between the valve body and the valve cover 1. Packing leakage – Causes: 1) Principle of packing sealing: An axial force is applied to the packing, causing it to undergo plastic deformation. Due to the multiple packings installed in the valve, different areas come into contact with each other alternately, creating a \"labyrinth effect\" that prevents the pressure medium from leaking out. 2) Packing leakage is caused not only by insufficient contact pressure of the packing due to differences in pressure and permeability of the medium, but also by aging of the packing itself and damage to the valve stem. 3) The packing corrodes the valve stem; therefore, when pressure causes the medium to leak outward through the gap between the packing and the valve stem, until leakage occurs at the packing site. Additionally, improper operation and excessive force can cause the valve stem to bend. 4) The filler was selected improperly; it is not resistant to corrosion by the medium, nor to high pressure or vacuum, high temperatures, or low temperatures. 5) The filler has exceeded its service life, has aged, and lost its elasticity. 6) Insufficient number of fillers installed. Solution: 1) The type and material of filler should be selected based on the operating conditions ； 2) Pre-tighten the packing, install it correctly, and determine the appropriate amount of packing ； 3) Bent valve stem, surface corrosion – mechanical repair or replacement ； 4) The filler must be replaced if it becomes ineffective. IV. Flange leakage: 1. For the sealed connection of the valve’s flanges, gaskets are placed at the contact points as required by the design; the pre-tightening force generated by the connecting bolts ensures a sufficient specific pressure to prevent the medium from leaking outward. 2. Gasket materials and types include: rubber gaskets, asbestos-rubber gaskets, graphite gaskets, stainless steel and graphite wound gaskets, bellows-type gaskets, and metal gaskets. 3. Gasket sealing belongs to forced sealing. 4. Common flange leaks include the following: 1) Interface leakage – leakage occurs due to a poor seal between the gasket and the flange surface. Main reasons: Insufficient pre-tightening force of the n gasket – Solution: Increase the pre-tightening force appropriately; Roughness of the n flange sealing surface not meeting requirements – Solution: Repair it; The n flange surface is uneven or has horizontal scratches – Solution: Repair it; Cold and heat deformation, as well as mechanical vibrations – Solution: Improve the environment or select different materials; Deformation and elongation of the n flange connection bolts – Solution: Use appropriate materials and ensure that the allowable torque is not exceeded; Plastic deformation of the n gasket due to long-term use – Solution: Replace it; Aging, cracking, and deterioration of the n gasket – Solution: Replace it. 2) Seepage leakage – Leakage occurs as the medium, under pressure, passes through the gaps in the gasket material. Main reason: n is related to the material of the sealing gasket ； n Pressure of the medium ； n Temperature of the medium ； n The sealing gasket is aged, cracked, and deteriorated. 3) Damage-induced leakage – Leakage that occurs due to excessive compression of the gasket or insufficient sealing pressure resulting from poor installation quality. Main reason: The installation of the sealing gasket is skewed, resulting in insufficient local sealing pressure or excessive pre-tensioning, thereby losing its resilience ； l The flange connection bolts are not evenly tightened ； l Coaxiality of the two flanges (offset of the center lines) deviation ； If the sealing gasket is not selected properly, that is, if the material and type of gasket are not chosen appropriately based on the operating conditions ； Interface leakage and damage-induced leakage tend to increase significantly over time, while the relationship between the amount of permeation leakage and time is not distinct.