Valve specifications and categories should meet the requirements of pipeline design documents
The model of the valve should indicate the requirements of the national standard number on which it is based. If it is an enterprise standard, the relevant description of the model should be indicated
The working pressure of the valve is required to be greater than or equal to the working pressure of the pipeline. On the premise of not affecting the price, the working pressure that the valve can withstand should be greater than the actual working pressure of the pipeline. When the valve is closed, any side should be able to withstand 1.1 times the working pressure of the valve without leakage; when the valve is open, the valve body should be able to withstand twice the working pressure of the valve.
The valve manufacturing standard should indicate the national standard number based on it. If it is an enterprise standard, the purchase contract should be attached to the enterprise document
Select valve material
Valve material, since gray cast iron pipes are gradually not recommended, the valve body material should be mainly ductile cast iron, and the grade and the actual physical and chemical testing data of the casting should be indicated.
Stem material, strive to use stainless steel stem (20Cr13), large-diameter valves should also use stainless steel embedded stem.
Nut material, the nut is made of cast aluminum brass or cast aluminum bronze, and its hardness and strength are greater than that of the valve stem.
Material of stem bushing, the hardness and strength of the valve stem bushing should not be greater than that of the valve stem, and there should be no electrochemical corrosion with the valve stem and valve body under water immersion.
Material of sealing surface:
- Different valve types, different sealing methods and material requirements.
- For ordinary wedge gate valves, the material, fixing method and grinding method of the copper ring should be explained.
- Soft sealing gate valve, physicochemical and hygienic testing data of valve plate rubber lining material
- The butterfly valve should be marked with the material of the sealing surface on the valve body and the material of the sealing surface on the butterfly plate; Their physical and chemical testing data, especially the hygienic requirements of rubber, anti-aging performance, and wear resistance; usually NBR and EPDM rubber, etc. are used, and reclaimed rubber is strictly prohibited.
Material of valve shaft
Since the valves in the pipe network are usually opened and closed infrequently, the packing is required to be inactive for several years, and the packing will not age, so that the sealing effect can be maintained for a long time;
The valve shaft packing should also keep the good sealing effect when it is subjected to frequent opening and closing.
In view of the above requirements, the valve shaft packing strives not to be replaced for life or more than ten years;
If the packing needs to be replaced, the valve design should consider measures to be replaced under the condition of water pressure
Gearbox
The box material and internal and external anti-corrosion requirements are consistent with the valve body principle.
The box body should have sealing measures. After the box body is assembled, it can withstand immersion in a water column of 3 meters.
For the opening and closing limit device on the box, its adjusting nut should be in the box.
The design of the transmission structure is reasonable. When opening and closing, it can only drive the valve shaft to rotate, not to make it move up and down. The transmission parts bite properly, and do not separate and slip when opening and closing with a load.
The box body and the valve shaft seal should not be connected to form a leak-free whole
There is no debris in the box, and the gear occlusion part should be protected by grease
Valve operating mechanism
The opening and closing direction of the valve should always be closed clockwise.
Since the valves in the pipe network are often opened and closed manually, such as fully welded ball valve, the opening and closing revolutions should not be too many, even large-diameter valves should be within 200-600 revolutions.
In order to facilitate the opening and closing operation of one person, the maximum opening and closing torque should be 240m-m under the condition of pipeline work pressure.
The opening and closing operation end of the valve should be a square tenon with standardized dimensions and face the ground, so that people can directly operate it from the ground. Valves with discs are not suitable for underground pipe networks.
Valve opening and closing degree display panel
- The scale line for the degree of valve opening and closing should be cast on the gearbox cover or on the casing of the display panel after changing the direction, all facing the ground, and the scale line should be painted with fluorescent powder to show eye-catching
- The material of the indicator dial needle can be made of stainless steel plate under the condition of good management, otherwise it is painted steel plate, do not use aluminum skin;
- The indicator dial needle is eye-catching and firmly fixed. Once the opening and closing adjustment is accurate, it should be locked with rivets.
- If the valve is buried deep, and the distance between the operating mechanism and the display panel is ≥15m from the ground, there should be an stem extension facility, and it should be fixed firmly so that people can observe and operate from the ground. That is to say, the valve opening and closing operation in the pipeline network is not suitable for downhole operation.
Valve performance testing
When a valve is manufactured in batches of a certain specification, an authoritative organization should be entrusted to carry out the following performance tests:
- Opening and closing torque of valve under working pressure
- Under the condition of working pressure, the continuous opening and closing times of the valve can be guaranteed to be tightly closed.
- Detection of the flow resistance coefficient of the valve under the condition of pipeline water delivery
The valve should be tested as follows before leaving the factory:
- When the valve is open, the valve body should withstand the internal pressure detection of twice the working pressure value of the valve.
- When the valve is closed, both sides are subjected to 11 times the working pressure value of the valve, and there is no leakage; but the leakage value of the metal-sealed butterfly valve is not greater than the relevant requirements.
Internal and external corrosion protection of valves
The inside and outside of the valve body (including the gearbox body), first of all, shot blasting and cleaning should be done to remove rust, and strive to electrostatically spray powder non-toxic epoxy resin with a thickness of more than 0.3mm. When it is difficult to electrostatically spray non-toxic epoxy resin for extra-large valves, similar non-toxic epoxy paint should also be brushed and sprayed.
The inside of the valve body and various parts of the valve plate require comprehensive anti-corrosion. On the one hand, it will not corrode when immersed in water, and there will be no electrochemical corrosion between the two metals; on the other hand, the surface is smooth to reduce the water resistance.
The hygienic requirements of the anti-corrosion epoxy resin or paint in the valve body should have the test report of the corresponding authority. The chemical and physical properties should also meet the relevant requirements.
Valve packaging and transportation
Lightweight blocking plates should be installed on both sides of the valve to seal
Medium and small diameter valves should be bundled with straw ropes and transported in containers.
Large-diameter valves are also packaged with a simple wooden frame to prevent damage during transportation.
View the valve’s factory manual
The valve is equipment, and the following relevant data should be indicated in the factory manual: Valve specification; model; Working pressure; Manufacturing standard; Valve body material; Stem material; Sealing material; Valve shaft packing material; Stem bushing material; Internal and external anti-corrosion material; Operation start direction; Number of revolutions; Opening and closing torque under working pressure
The name of the manufacturer; The date of manufacture; The serial number; Weight; The diameter of the connecting flange, the number of holes, the center hole distance, and the control dimensions of the overall length, width and height are indicated in the diagram; Effective opening and closing times; Valve flow resistance coefficient; Relevant data of valve factory inspection and precautions for installation and maintenance, etc.