When purchasing valves, many people only specify the valve specifications, type, and working pressure. However, in today’s market economy, this approach is incomplete. Valve manufacturers develop their own enterprise standards and product characteristics based on unified design concepts to enhance competitiveness. Therefore, it is essential to propose detailed technical requirements, coordinate with manufacturers to reach a consensus, and include these details as an appendix to the valve procurement contract. Today, COVNA will discuss the factors to consider when purchasing valves.
I. General Requirements for Valves
1. The valve specifications and types should meet the requirements of the pipeline design documents.
2. The valve model should indicate the national standard reference number. If an enterprise standard is used, relevant details should be specified.
3. The valve’s working pressure should be equal to or greater than the pipeline’s working pressure. If cost permits, the valve’s pressure tolerance should exceed the actual working pressure of the pipeline. The valve must withstand one-time working pressure on either side in the closed position without leakage. In the open position, the valve body should endure twice the working pressure.
4. The manufacturing standards of the valve should reference national standard numbers. If an enterprise standard is used, it should be included in the procurement contract.
II. Valve Material
1. Valve Body Material: Mainly ductile iron, with grade and physical-chemical test data provided.
2. Valve Stem Material: Preferably stainless steel (2CR13); large-diameter valves should also have stainless steel-coated stems.
3. Nut Material: Should be cast aluminum bronze or cast aluminum brass, with higher hardness and strength than the valve stem.
4. Stem Bushing Material: Hardness and strength should be lower than the valve stem, and it should not cause electrochemical corrosion with the valve stem or body when submerged in water.
5. Sealing Surface Material:
• Different valve types require different sealing methods and materials.
• For wedge gate valves, specify the copper ring material, fixing method, and grinding process.
• For soft-seal gate valves, provide physical, chemical, and hygiene test data for the rubber material.
• For butterfly valves, specify the sealing materials of both the valve body and disc, along with chemical and physical test data. Rubber materials should meet hygiene requirements, resist aging, and have high wear resistance (e.g., NBR, EPDM). The use of recycled rubber is strictly prohibited.
6. Valve Stem Packing:
• Must remain effective for years without movement or aging.
• Should maintain a good seal even under frequent opening and closing.
• Preferably maintenance-free or with a lifespan exceeding ten years.
• If replacement is necessary, the design should allow for replacement under pressure.
III. Gear Transmission Box
1. The material and anti-corrosion requirements should match the valve body.
2. The gearbox must be sealed and withstand submersion under a 3-meter water column.
3. The opening and closing limit adjustment nut should be inside the gearbox or secured externally with a special tool.
4. The transmission structure should ensure smooth valve stem rotation without axial movement.
5. The sealing between the gearbox and valve stem should prevent leakage.
6. The gearbox should be free of debris, and gear engagement areas should be lubricated.
IV. Valve Operating Mechanism
1. All valves should close clockwise.
2. To facilitate manual operation, the number of turns required for opening/closing should be limited (200-600 turns for large valves).
3. The maximum operating torque under pipeline pressure should not exceed 240N·m.
4. The valve operation end should have a standardized square stem facing the ground for direct manual operation. Valves with handwheels are unsuitable for underground pipelines.
5. Opening and Closing Indicator:
• The scale should be cast on the gearbox cover or external casing, facing the ground, and coated with fluorescent paint.
• The indicator needle should be stainless steel or painted steel (not aluminum) for durability.
• The needle should be securely fastened and locked after calibration.
6. Extension Rods: If the operating mechanism and indicator are more than 5 meters above ground, extension rods should be installed and firmly fixed for easy operation and monitoring. Underground valves should not require entry into a pit for operation.
V. Valve Performance Testing
1. For mass production, a third-party authority should conduct the following tests:
• Torque test under working pressure.
• Seal durability test under continuous opening/closing cycles.
• Flow resistance coefficient test under water flow conditions.
2. Factory tests before shipment should include:
• Pressure test in the open position, ensuring the valve body withstands twice the working pressure.
• Pressure test in the closed position, ensuring both sides can withstand one-time working pressure without leakage (for metal-seated butterfly valves, leakage must not exceed allowable limits).
VI. Valve Internal and External Anti-Corrosion
• The valve body (including gearbox) should be shot-blasted and coated with non-toxic epoxy resin via electrostatic spraying, with a thickness of at least 0.3mm. For large valves where electrostatic spraying is impractical, equivalent epoxy paint should be applied.
• The entire valve interior and disc surface should be coated to prevent corrosion and electrochemical reaction between different metals. The smooth surface also helps reduce water resistance.
• The epoxy resin or paint used must have certified hygiene compliance and meet relevant chemical and physical standards.
VII. Valve Packaging and Transportation
• Lightweight sealing plates should be placed on both valve ends.
• Small and medium-sized valves should be tied with straw rope and preferably transported in containers.
• Large-diameter valves should have a simple wooden frame to prevent damage during transport.
VIII. Valve Factory Documentation
Valves are equipment, so the factory documentation should specify the following:
• Valve specifications and model
• Working pressure
• Manufacturing standards
• Material details (body, stem, sealing, packing, bushing)
• Corrosion protection details
• Operational direction and number of turns
• Operating torque under pressure
• Manufacturer name, production date, serial number, and weight
• Flange specifications (hole diameter, number of holes, and center distance)
• Dimensional diagram (length, width, height)
• Flow resistance coefficient
• Effective lifespan and number of opening/closing cycles
• Factory test results and installation/maintenance instructions
COVNA Industrial Automation Co., Ltd. specializes in the research, design, sales, and service of high-end control valves, aiming to become a global automation solutions provider. With 19 years in the valve industry, COVNA has developed an independent intellectual property system and received multiple high-tech achievements awards in Dongguan, China. In 2017, COVNA was honored as a high-tech enterprise.
For industrial valve procurement, choose COVNA!
