Valve specifications and types should comply with the requirements of the pipeline design documents.
1. The valve model should indicate the national standard number based on which it is based. If it is a company standard, the model number should be clearly stated.
2. The valve operating pressure must be ≥ the pipeline operating pressure. Without affecting the price, the valve should withstand an operating pressure greater than the actual pipeline operating pressure. When the valve is closed, each side should be able to withstand 1.1 times the valve operating pressure without leakage. When the valve is open, the valve body should be able to withstand twice the valve operating pressure.
3. The valve manufacturing standard should indicate the national standard number based on which it is based. If it is a company standard, the company document should be attached to the purchase contract.
Selecting the valve material
1. For valve material, gray cast iron pipes are gradually being deprecated. The valve body material should primarily be ductile iron. The grade and actual physical and chemical test data of the casting should be clearly stated.
2. For valve stem material, stainless steel stems (20Cr13) should be preferred. Large-diameter valves should also have stainless steel insert stems.
3. Nut material: Use cast aluminum brass or cast aluminum bronze, and its hardness and strength should be greater than that of the valve stem.
4. The material of the valve stem bushing should be no harder or stronger than that of the valve stem, and should not cause electrochemical corrosion with the valve stem and valve body when immersed in water.
5. Sealing surface material:
① Different valve types have different sealing methods and material requirements.
② For ordinary wedge-type gate valves, the material, fixing method, and grinding method of the copper ring should be clearly stated.
③ For soft-seal gate valves, the physical, chemical, and hygienic test data of the valve disc lining rubber material should be clearly stated.
④ For butterfly valves, the material of the valve body sealing surface and the material of the disc sealing surface should be clearly stated, along with their physical and chemical test data, especially the hygienic requirements, aging resistance, and wear resistance of the rubber. Typically, NBR and EPDM rubber are used; the use of recycled rubber is strictly prohibited.
6. Valve Shaft Packing
① Since valves in pipeline networks are typically opened and closed infrequently, the packing must remain inactive for several years and not age, ensuring long-term sealing.
② Valve shaft packing must also maintain a good sealing performance despite frequent opening and closing.
③ Given the above requirements, valve shaft packing should ideally not be replaced for life or for over ten years.
④ If packing replacement is necessary, the valve design should allow for replacement under water pressure.
Valve Operating Mechanism
1. Valves should always be opened and closed in a clockwise direction.
2. Since valves in pipeline networks are often opened and closed manually, the number of opening and closing revolutions should be limited. Even large-diameter valves should be within 200-600 revolutions.
3. To facilitate single-person operation, the maximum opening and closing torque should be 240mm under pipeline pressure.
4. The valve operating end should have a square tenon, standardized dimensions, and face the ground for direct operation from the ground. Valves with rotary dials are not suitable for use in underground pipe networks.
5. Valve Opening/Closing Amplitude Indicator
① The valve opening/closing degree scale should be cast on the transmission cover or on the outer casing of the indicator panel after the direction is reversed. It should always face the ground, and the scale should be painted with fluorescent powder for visibility.
② The indicator needle can be made of stainless steel under good management. Otherwise, it should be painted steel. Aluminum should never be used.
③ The indicator needle should be visible and securely fixed. Once the opening/closing adjustment is accurate, it should be locked with rivets.
6. If the valve is buried deep, and the operating mechanism and indicator panel are 15 meters or more above the ground, an extension rod should be installed and securely fixed to facilitate observation and operation from the ground. In other words, valve opening and closing operations in the pipe network should not be performed underground.
Valve Performance Testing
1. When mass-producing a valve of a certain specification, the following performance tests should be conducted by a reputable organization:
① Valve opening and closing torque under operating pressure;
② Number of consecutive opening and closing cycles required to ensure tight closure under operating pressure;
③ Valve flow resistance coefficient under pipeline water flow conditions.
2. Valves should undergo the following tests before shipment:
① When the valve is open, the valve body must withstand an internal pressure equal to twice the valve's operating pressure;
② When the valve is closed, both sides must withstand one times the valve's operating pressure, with no leakage. However, for metal-sealed butterfly valves, the leakage value must not exceed the relevant requirements.
Valve Internal and External Corrosion Protection
1. The valve body should first be shot blasted to remove rust and sand. Efforts should be made to electrostatically spray-coat the valve with powdered non-toxic epoxy resin to a thickness of at least 0.3 mm. If electrostatic spraying of non-toxic epoxy resin is difficult for oversized valves, a similar non-toxic epoxy paint should be applied by brushing or spraying.
2. The interior of the valve body and all parts of the valve disc must be fully corrosion-resistant. Firstly, they must resist rusting when immersed in water and prevent electrochemical corrosion between the two metals. Secondly, their smooth surfaces minimize water resistance.
3. The hygienic requirements of the epoxy resin or paint used for corrosion protection inside the valve body must be accompanied by a test report from the relevant authority. Chemical and physical properties must also meet relevant requirements.
Valve Packaging and Transportation
1. Lightweight plugs should be installed on both sides of the valve to secure it.
2. Medium and small-diameter valves should be tied with straw rope and preferably transported in a container. 3. Large-diameter valves are also packaged in a simple wooden frame to prevent damage during transportation.
Check the valve's factory manual.
1. Valves are equipment. The factory manual should include the following relevant data: valve specifications; model; working pressure; manufacturing standards; valve body material; valve stem material; seal material; valve shaft packing material; valve stem sleeve material; internal and external corrosion protection materials; operating direction; speed; opening and closing torque under operating pressure conditions.
2. Manufacturer's name; date of manufacture; factory serial number; weight; connecting flange diameter, number of holes, and center-to-center hole spacing. Graphically indicate the overall length, width, and height control dimensions; effective opening and closing times; valve flow resistance coefficient; relevant valve factory inspection data, and installation and maintenance precautions.