In industrial production, the knife gate valve is an indispensable piece of equipment primarily used to control the flow of fluids. However, due to long-term use, improper operation, or environmental factors, knife gate valves may develop various problems that affect their normal operation. This article provides a detailed introduction to the common problems encountered during the use of knife gate valves and their corresponding solutions, helping you better maintain and manage knife gate valves to ensure the reliability of industrial fluid control.
In industrial production, as a key device for controlling fluid flow, the performance and reliability of a knife gate valve are directly related to the smoothness of production processes. However, due to long-term use, improper operation, or environmental factors, knife gate valves may encounter various issues that not only affect production efficiency but may also cause safety hazards. Therefore, understanding the common problems of knife gate valves and their solutions is crucial for ensuring stable industrial operations.
Stem rotation is not smooth or becomes stuck: There are various reasons why a valve stem may rotate poorly or become stuck. First, overly tightened packing increases friction on the stem, making rotation difficult. Second, packing that is not installed according to specifications may result in improper fit between packing and stem. Additionally, insufficient clearance between the stem and the bushing, stem bending, improper surface roughness of the thread, and incorrect material selection for the stem and stem sleeve can all affect normal stem rotation.
To address these problems, slightly loosen the packing gland bolts to reduce pressure on the stem. Follow standard procedures when adding packing to ensure even distribution. Maintain the clearance between the stem and the bushing within standard limits. Straighten the stem to ensure proper alignment. Control the surface roughness of thread machining within required standards. Choose appropriate materials for both the stem and stem sleeve to avoid galling between materials.
Stem failure: Stem failure is mostly caused by excessive force during operation, which damages the stem threads or bends the stem, or due to improper tolerance fit between stem and nut, nut inclination, corrosion of threads by the medium, or rusting. In addition, unsuitable material selection, such as using the same material for both the stem and the stem nut, making them prone to galling, can also result in stem failure.
When operating a knife gate valve, workers should handle it carefully. When opening and closing, they should control the force strictly and avoid violent switching to prevent bending of the stem. The valve should not be opened to the upper dead point; after moderate opening, turn the handwheel back one full turn so the upper side of the thread fits tightly to avoid medium pressure pushing the stem upward. Meanwhile, adjust the nut position appropriately. If corrosion or rust is unavoidable, replace the stem and nut in time, and use nuts and stems made of different materials to reduce the possibility of galling.
Leakage from bonnet pressure test hole: Some manufacturers include pressure test holes in the bonnet, which may cause leakage during use. The main reason is loose sealing of the test hole.
Re-tighten the bolts of the pressure test hole. If the bolt is damaged, remove it and take out the copper gasket inside, clean the threaded hole, and then reinstall the bolt. Weld the area with electric welding to ensure sealing of the pressure test hole.
Leakage at the connection between the bonnet and valve body: Insufficient or uneven bolt tightening at the flange connection may cause flange misalignment and result in leakage at the connection between the valve body and the bonnet. In addition, damage to the sealing surface between the valve body and bonnet or damage to the flange gasket can also lead to leakage.
It is best to tighten the flange using a crisscross pattern to ensure uniform bolt tension. During use, protect the sealing surfaces from damage. Choose high-quality gaskets. If the gasket cannot compensate for the sealing surface defect, the sealing surface may need to be reprocessed to ensure proper sealing.
Leakage of the sealing surface: The causes of sealing surface leakage include poor grinding of the sealing surface, poor fit of the sealing ring with the seat or gate, loose connection between gate and stem, misalignment caused by stem bending or twisting, excessively fast closing causing poor contact of the sealing surface, improper material selection that cannot resist corrosion by the medium, using globe or gate valves for throttling causing sealing surfaces to erode under high-speed fluid impact, medium cooling causing cracks and erosion on sealing surfaces, corrosion or loosening caused by oxygen concentration cells formed at threaded connections between sealing rings and valve seats or gates, and impurities such as welding slag, rust, and dust becoming embedded in the sealing surface or blocking the gate, preventing tight closure.
Check the condition of the sealing surface. If damage or looseness is detected, adjust the sealing surface to make it fit more tightly, reducing leakage. The sealing surface can also be replaced with high-quality materials and correctly installed. Select proper valve materials to enhance corrosion and erosion resistance. Avoid closing too quickly to ensure proper sealing contact. Regularly clean impurities inside the valve to prevent them from embedding into the sealing area or blocking the gate.
Leakage from the packing gland: Causes include packing not suitable for the corrosiveness, temperature, or pressure of the working medium; incorrect packing method, especially inserting a whole strip of packing directly; insufficient machining accuracy or smoothness of the stem; stem pitting or rust from outdoor exposure; stem bending; aging of packing due to long-term use; and excessive operation force.
Choose the correct packing material and method, and install packing properly. Use valve stems with proper surface finish and apply protective measures to prevent corrosion. Replace the stem in case of rusting. Avoid excessive force during operation to prevent thread damage or stem bending.
Poor sealing of the valve seat: Poor valve seat sealing may be due to inherent quality issues or improper installation.
Inspect the condition of the valve seat and repair or replace it as needed. Use sealing compounds or gaskets to improve sealing performance and ensure proper sealing of the valve seat.
Cracking of the valve body: Valve body cracking is generally caused by freezing. In cold weather, if the knife gate valve is not equipped with insulation or heating measures, the fluid inside may freeze and expand, causing the valve body to crack. In cold weather, apply insulation or heating measures such as insulating materials or heating devices to prevent freezing. During design and installation, consider environmental effects and choose suitable insulation materials and heating devices to ensure proper operation in low temperatures.
Handwheel damage: Handwheel damage is usually caused by impact or excessive force using a long lever. Operators should avoid impacts and follow operating procedures strictly. Avoid using long levers for forceful operation. Regularly inspect handwheel condition and repair or replace damaged ones in time.
Packing gland fracture: Packing gland fracture may be caused by uneven force during tightening or inherent defects in the gland. When tightening, rotate screws symmetrically to ensure even force. During manufacturing, ensure high quality not only for major components but also secondary components like the gland, preventing defects and improving service life.
Failure of connection between stem and gate: Knife gate valves commonly use a rectangular stem head connecting to a T-slot on the gate. Sometimes the T-slot is not properly machined, causing rapid wear of the stem head. This issue must be resolved during manufacturing by ensuring machining accuracy and surface smoothness. Users may also reprocess the T-slot to improve finish, reducing wear and improving connection reliability.
To extend the service life of knife gate valves and ensure their normal operation, regular maintenance and care are essential. Below are recommendations for maintaining and caring for knife gate valves.
Conduct periodic comprehensive inspections of all parts including the stem, bonnet, sealing surface, packing chamber, and valve seat. Check for damage, looseness, corrosion, or leakage, and repair or replace parts as needed. Also check whether the valve operates smoothly and whether there is any sticking, ensuring proper opening and closing.
Regularly clean internal impurities and dirt to avoid affecting sealing performance and operation. Lubricate moving parts such as the stem to reduce friction and prevent damage caused by excessive friction. Ensure that lubricants are of proper quality and compatible with the valve to avoid damage from unsuitable lubricants.
In harsh environments, knife gate valves are prone to corrosion and rust. Therefore, apply appropriate anti-corrosion measures such as anti-corrosion coatings or corrosion-resistant materials. Pay attention to rust prevention for components like stems. Conduct regular checks for rust and apply timely derusting and protective treatments.
Operators must strictly follow standard procedures, avoiding forceful switching, impacts on the handwheel, or use of long levers. Control force and speed during opening and closing to avoid unnecessary damage. Provide regular training to improve operation skills and safety awareness, ensuring safe operation.
Different environments affect knife gate valves in different ways. During installation and use, consider environmental factors and adopt appropriate measures. For example, in cold environments, apply insulation and heating; in humid environments, use moisture protection; in corrosive media environments, select corrosion-resistant materials. This ensures proper operation under various conditions.
Selecting high-quality knife gate valves is fundamental to ensuring proper operation. Consider the following.
Choose well-known brands and reputable manufacturers, as they typically use advanced technology and strict quality control, ensuring high performance and reliability. Their after-sales services are also more complete, providing timely technical support.
Material and manufacturing processes greatly affect performance and service life. Select appropriate materials for the valve body, bonnet, stem, sealing surface, etc., with strong strength, corrosion resistance, and sealing capability. Pay attention to workmanship such as welding quality, machining accuracy, and surface treatment.
Select specifications and models according to actual working requirements. Consider nominal pressure, nominal diameter, working temperature, media type, etc., ensuring suitability. Choose appropriate connection types and dimensions based on pipeline layout and installation space.
Choose valves that have passed relevant certifications and comply with standards. Certifications ensure compliance with safety, performance, and environmental requirements. Examples include ISO9001, ISO14001, and national, industry, or international standards.
Knife gate valves play an important role in industrial production, but various problems may occur during use. Proper understanding of these problems and solutions, combined with correct maintenance, care, and high-quality valve selection, ensures stable and reliable operation of industrial systems.
