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The integrity rate of the valve is related to the selection of the valve, the manufacture of the valve, the design of the pipeline, the installation of the valve, and the daily operation management of the opening and closing operation. The causes of valve failure are mainly concentrated in valve quality, logistics, hoisting operations, warehousing, construction, operation, daily management and maintenance. Valve damage is mainly caused by excessive operating force, material, corrosion and other reasons.
Anti-corrosion coating and coating requirements
Anti-corrosion layer: Individual valve manufacturers did not strictly formulate or implement production processes according to international requirements, resulting in serious corrosion of the valve cavity, resulting in water quality problems, and damage to the valve cavity in severe cases.
Coating: No matter what the appearance of the product is, it is the first impression of the product. The location where the valve is installed, usually in a damp space, sometimes even immersed in water. Therefore, the coating material of the valve should meet the sanitary standards of drinking water, non-toxic, corrosion-resistant, wear-resistant and so on.
A valve is composed of different materials, that is, metal and non-metal, which can easily cause electrochemical corrosion.
According to the above problems, we must choose the products that meet the national standards and relevant regulations in terms of management and production process, so as to ensure the water quality of water supply and the guarantee of safe service life.
During the initial acceptance of the valve, the anti-corrosion layer and coating of the valve shall be sampled for thickness, adhesion, hardness, insulation, impact resistance, etc. according to the standard.
Frequently Asked Questions about Sealing
The sealing performance refers to the ability of each sealing part of the valve to prevent the leakage of the medium, which is the most important technical performance index of the valve.
Commonly used seals in valves are non-metallic and metal. Non-metallic seals usually use rubber (EPDM, nitrile, etc.), and metal seals include copper, steel, stainless steel, etc.
After being used for a long time, some rubber will become sticky and soft, and some will harden and become brittle. The cracks that produce the ridges are called cracks professionally. In this case, the original elasticity and strength of the rubber decrease significantly, and these phenomena are called aging.
During the movement of the metal seal, the metal-metal friction creates a gap, which reduces the sealing performance.
How to find out which of the above situations occurs, regularly judge by looking (appearance, pressure difference before and after closing, etc.), listening, and detecting instruments. If there is any problem, replace and repair it in time to avoid water accidents.
Causes and Treatment of Valve Body Leakage
Causes:
The valve body has blisters or cracks, and the valve body is cracked during repair welding.
Processing method:
For suspected cracks, etch with 4% nitric acid solution to see if there are cracks. If there are cracks, repair the cracks.
The valve stem and matching thread are damaged or the valve stem is broken, the reason and treatment of bending
Causes:
Improper operation, excessive force when opening and closing, the limit device fails, the over-torque protection does not act, and the thread fit is too tight or too loose. Too many operations and long service life.
Approach:
Improve the operation method, check the limit and over-force protection devices, select the appropriate screw and nut thread matching, and replace the matching parts of the same type.
The reason and treatment of water leakage of valve cover
The leakage of the valve cover is called external leakage, that is, the medium leaks from the inside of the valve to the outside of the valve. The external leakage will cause material loss, pollute the environment, and even cause accidents in serious cases.
Causes:
The bolt is loose or one side is too tight. Damaged gasket. Defective gasket mating surface.
Processing method:
Adjust the tightness of the bolts so that the gap between the pressure plate and the flange is consistent. Replace the gasket. Disassemble and repair the gland sealing surface.
Causes and Treatment of Valve Internal Leakage
Internal leakage of the valve will affect the ability of the valve to cut off the medium. For the cut-off valve, internal leakage is not allowed.
Causes:
Water leaks after closing. Sealing treatment joint surface wear, aging, etc. The connection between the valve disc and the valve stem is too large intermittently, causing the valve disc to sag or have poor contact. Poor sealing or disc jamming.
Processing method:
Turn on and off repeatedly. Disassemble the valve, repair and grind the valve disc and valve seat sealing surface or replace the sealing ring. Adjust the clearance between the disc and the stem or replace the disc. Disassemble valve to eliminate jamming or replace sealing material.
The valve disc and valve stem fall off, causing switch failure reasons and treatment
Causes:
Corrosion over time or improper previous repairs. The opening or closing force is too large, causing damage to the junction of the valve disc and the valve stem. The disc stopper is loose or the link part is worn.
Processing method:
After overhaul, check or replace corrosion-resistant parts. During operation, it is not advisable to use too much force to switch, and replace the valve disc or valve stem.
Replace damaged parts.
Causes and treatment of cracks in valve disc and valve seat
Causes:
There is a problem with the quality of the surfacing welding of the joint surface or the quality of the casting. The temperature difference around the valve is large.
Processing method:
Repair welding, make corresponding heat treatment, and then carry out grinding and so on. Replace the valve according to the actual situation.
Reasons and solutions for the inflexibility of the valve stem or the inability of the switch to move
Causes: Infrequent switching, in a static state, rust, adhesion, etc. at the transmission of the valve. The packing is too tight or the sealing ring is broken. The valve stem clearance is too small, causing it to swell to death. The valve stem and the nut are too tight or the matching screw is damaged. The stem and disc are bent. The medium temperature is too high, the lubrication is poor, and the valve stem is severely corroded.
Processing method:
Whenever possible, look for conditions to activate the valve periodically. After slightly loosening the packing or sealing ring gland, try opening it. Appropriately increase the valve stem clearance. Replace stem and nut. Correct disc, stem or replace. Use pure graphite powder as lubricant.
Causes and Treatment of Packing Leakage
Causes:
The filler has been used over time and has aged. The packing follower is not compressed or biased. Damaged stem surface. Incorrect packing material.
Processing method:
Replace the packing and place it one by one, and the interface is about 30 degrees. Readjust the packing gland. Repair or replace valve stem. Correct choice of filler.
The reason and treatment of the worm gear bite jam
Causes:
There are foreign objects or grease failure, etc. Careless operation, excessive wear of the turbine, and the bearing bite.
Processing method:
Remove foreign objects and make minor repairs. Re-replace the turbine, if it is found to be stuck during operation, if the resistance is too large, it should be stopped immediately and checked in time.
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