In today’s market economy, the procurement of valves is not solely based on clear specifications, types, and pressure requirements. The current system lacks completeness, as valve manufacturers, in their competition for contracts, often adopt a unified design concept with varying innovations, leading to the development of their own corporate standards and product identities. Therefore, it is essential that when procuring valves, more detailed technical requirements are defined, and manufacturers reach consensus before finalizing the contract, which should include these specifications as an annex.
1. General Requirements
1.1 The valve specification and category must align with the pipeline design documents.
1.2 The valve type should be marked according to national standard numbers. If using an enterprise standard, the model description must be clearly stated.
1.3 The working pressure of the valve must be greater than or equal to the pipeline pressure. Under normal conditions, the valve should withstand at least 1.1 times its rated pressure without leakage. When open, the body must endure double the rated pressure.
1.4 The manufacturing standard should follow national codes. If enterprise standards are used, the relevant documentation must accompany the procurement contract.
2. Valve Quality
2.1 The body material should primarily be ductile iron, with grades and physical/chemical test results clearly indicated.
2.2 The stem material should preferably be stainless steel (e.g., 2CR13), and large-diameter valves should use stainless steel embedded stems.
2.3 The nut material should be cast aluminum brass or bronze, with higher hardness and strength than the stem.
2.4 The stem bushing material should have lower hardness and strength than the stem, and should not cause electrochemical corrosion when exposed to water.
2.5 Sealing surface materials vary by valve type:
- Wedge gate valves should specify copper ring materials, fixing methods, and grinding techniques.
- Soft-seal gate valves require rubber lining with chemical and health testing data.
- Butterfly valves must indicate sealing material on both the body and disc, including anti-aging, wear resistance, and hygiene properties. NBR and EPDM rubbers should not contain recycled materials.
2.6 Stem packing must remain effective for years without aging, maintain sealing, and allow replacement under water pressure conditions.
3. Transmission Gearbox
3.1 The material and anti-corrosion treatment should match those of the valve body.
3.2 The box must be sealed and able to withstand 3 meters of water immersion.
3.3 The opening/closing limit device should be inside the box, requiring special tools for adjustment.
3.4 The transmission mechanism must ensure smooth rotation without axial movement.
3.5 The gear box and valve shaft seal must be independent to prevent leaks.
3.6 The box must be clean, with gears protected by grease.
4. Valve Operating Mechanism
4.1 The valve should close clockwise.
4.2 Manual operation should not be too fast; large-diameter valves should rotate between 200–600 turns.
4.3 The maximum torque for manual operation should be ≤ 240N-m for ease of use.
4.4 The operating end should be a square tenon, standardized, and positioned downward for ground-level access. Valves with wheels are unsuitable for underground networks.
4.5 The display plate must show clear scale lines, be made of stainless steel or painted steel, and have a fixed, visible indicator needle.
4.6 For deeper installations, additional rods must be provided so operators can work from the surface.
5. Valve Performance Testing
5.1 Each batch of valves must undergo pressure testing, tightness checks, and flow resistance evaluation.
5.2 Factory tests include internal pressure twice the rated value when open, and 1.1 times the working pressure when closed, with no leakage.
6. Anti-Corrosion Treatment
6.1 The body and gearbox should be sand-blasted and coated with non-toxic epoxy resin (≥ 0.3mm thick). Larger valves may use brush-applied paint.
6.2 All parts must be fully protected against corrosion and electrochemical reactions.
6.3 Corrosion-resistant materials must meet health and physical/chemical standards, with test reports available.
7. Packaging and Transportation
7.1 Both sides of the valve should be sealed with light-blocking plates.
7.2 Small valves should be wrapped in straw and transported in containers.
7.3 Large valves should be packed in wooden frames to prevent damage during transport.
8. Factory Instructions
The factory manual must include: valve specifications, model, working pressure, standards, materials, sealing components, packing, operating direction, revolutions, torque, manufacturer details, weight, dimensions, flow resistance, inspection data, and maintenance instructions.
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