A stopcock valve is [1] a straight-through valve that opens and closes quickly, and is also commonly used for media with suspended particles due to the wiping effect of the movement between the screw seal surfaces and the complete protection against contact with the flowing medium when fully opened. Another important feature is that it is easy to adapt to multi-channel constructions, so that one valve can get two, three, or even four different flow channels. This simplifies the design of the piping system, reduces the amount of valves used, and reduces some of the connections required in the equipment.
How it works Valves with stopcock bodies with through-holes as opening and closing parts. The plug body rotates with the [2] stem to achieve opening and closing action. The small, unpacked, plug valve is also known as a “cocker”. The plug body of the plug valve is mostly a cone (there is also a cylindrical body), which is matched with the conical orifice surface of the valve body to form a sealing pair. The plug valve is the earliest type of valve used, with simple structure, fast opening and closing, and low fluid resistance. Ordinary plug valves rely on the direct contact between the finished metal plug body and the valve body to seal, so the sealing is poor, the opening and closing force is large, easy to wear, and usually can only be used in low pressure (not higher than 1 megapascal) and small diameter (less than 100 mm) occasions.
Classify
According to the structural form, it can be divided into four types: tight plug valve, self-sealing plug valve, plug valve and oil-injected plug valve. According to the channel form, it can be divided into three types: straight-through plug valve, three-way stopcock valve and four-way plug valve. There are also tube plug valves.
Plug valves are classified by use including: soft seal plug valves, oil-lubricated hard seal plug valves, poppet plug valves, three-way and four-way plug valves.
Advantages
1. The plug valve is used for frequent operation, and the opening and closing are fast and light.
2. The fluid resistance of the plug valve is small.
3. The plug valve has a simple structure, relatively small size, light weight and easy maintenance.
4. Good sealing performance.
5. It is not limited by the installation direction, and the flow direction of the medium can be arbitrary.
6. No vibration, low noise.
Soft-seal gate valves
Soft seal gate valve, industrial valve, soft seal gate valve opening and closing parts are rams, the direction of movement of the ram is perpendicular to the direction of fluid, the gate valve can only be fully open and closed, can not be adjusted and throttled. The ram has two sealing surfaces, the most commonly used mode gate valve two sealing surfaces form a wedge, the wedge angle varies with the valve parameters, the nominal diameter is DN50~DN1200, the operating temperature: ≤200°C.
Product principle
The gate plate of the wedge gate valve can be made into a whole, which is called a rigid gate; It can also be made into a ram that can produce a slight amount of deformation to improve its manufacturability and make up for the deviation of the sealing surface angle in the processing process, which is called the elastic ram.
Soft seal gate valves are divided into two types: open rod soft seal gate valve and dark rod soft seal gate valve. Usually there is a trapezoidal thread on the lifting rod, which changes the rotary motion into linear motion through the nut in the middle of the ram and the guide groove on the valve body, that is, the operating torque into the operating thrust. When the valve is opened, when the ram lift height is equal to 1:1 times the valve diameter, the flow of the fluid is completely unobstructed, but this position cannot be monitored during operation. In actual use, it is marked by the vertex of the stem, that is, the position that cannot be opened, as its fully open position. In order to account for lock-up due to temperature changes, it is usually opened to the apex position and then reverted back 1/2-1 turn as the position of the fully open valve. Therefore, the fully open position of the valve is determined by the position of the ram (i.e. the stroke). This type of valve should generally be installed horizontally in the pipeline.
General Requirements
1. The specifications and categories of soft seal gate valves should meet the requirements of pipeline design documents.
2. The model of the soft seal gate valve should indicate the national standard number requirements according to it. If it is an enterprise standard, the relevant description of the model should be indicated.
3. The working pressure of the soft seal gate valve requires the working pressure of the ≥ pipeline, without affecting the price, the working pressure that the valve can bear should be greater than the actual working pressure of the pipeline, and any side of the soft seal gate valve should be able to withstand 1.1 times the working pressure value of the valve without leakage;
4. The manufacturing standard of soft seal gate valve should indicate the national standard number based on it, and if it is an enterprise standard, the enterprise document should be attached to the procurement contract.
Second, the soft seal gate valve material
1. The material of the valve body should be cast iron, cast steel, stainless steel, 316L, and the grade and the actual physical and chemical test data of the cast iron should be indicated.
2. The stem material should strive for stainless steel stem (2CR13), and the large-diameter valve should also be a stainless steel inlaid stem.
3. The nut is made of cast aluminum brass or cast aluminum bronze, and the hardness and strength are greater than that of the valve stem.
4. The hardness and strength of the stem bushing material 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 the condition of water immersion.
5. The material of the sealing surface
(1) The types of soft seal gate valves are different, and the sealing methods and material requirements are different;
(2) For ordinary wedge gate valves, the material, fixing method and grinding method of the copper ring should be explained;
(3) Physicochemical and hygienic testing data of soft seal gate valve and valve plate lining material;
6. Valve shaft packing
(1) Because the soft seal gate valve in the pipe network is usually infrequent opening and closing, the packing is required to be inactive for several years, and the packing is not aged, and the sealing effect is maintained for a long time;
(2) The valve packing should also be permanent when it is subjected to frequent opening and closing;
(3) In view of the above requirements, the valve shaft packing strives not to be replaced for life or more than ten years;
(4) If the packing needs to be replaced, the design of the pneumatic valve should consider the measures that can be replaced under the condition of water pressure.
Third, the operating mechanism of the soft seal gate valve
3.1 The opening and closing direction of the soft seal gate valve during operation should be closed clockwise.
3.2 Because the pneumatic valve in the pipe network is often manually opened and closed, the number of opening and closing revolutions should not be too much, that is, the large-diameter valve should also be within 200-600 revolutions.
3.3 In order to facilitate the opening and closing operation of one person, the maximum opening and closing torque should be 240N-m under the condition of pipeline pressure.
3.4 The opening and closing operation end of the soft seal gate valve should be square tenon, and the size should be standardized, and face the ground, so that people can operate directly from the ground. Valves with disc discs are not suitable for use in underground networks.
3.5 display panel of the opening and closing degree of soft seal gate valve
(1) The scale mark of the opening and closing degree of the soft seal gate valve should be cast on the gearbox cover or on the shell of the display disc after changing direction, all facing the ground, and the scale mark should be brushed with phosphors to show eye-catching;
(2) The material of the indicator disc needle can be made of stainless steel plate under the condition of good management, otherwise it is a painted steel plate, and should not be made of aluminum skin;
(3) The indicator disc needle is eye-catching, fixed firmly, once the opening and closing adjustment is accurate, it should be locked with rivets.
3.6 If the soft seal gate valve is buried deep, and the distance between the operating mechanism and the display panel and the ground is ≥1.5m, it should be equipped with an extension rod facility, and it should be fixed firmly so that people can observe and operate from the ground. That is to say, the opening and closing operation of the valve in the pipe network is not suitable for underground operation.
Fourth, the performance test of the soft seal gate valve
4.1 When the valve is manufactured in batches of a certain specification, an authoritative organization should be entrusted to test the following performance:
(1) The opening and closing torque of the valve under the condition of working pressure;
(2) Under the condition of working pressure, it can ensure the continuous opening and closing times of the valve to close tightly;
(3) Detection of the flow resistance coefficient of the valve under the condition of pipeline water transportation.
4.2 The valve should be tested as follows before leaving the factory:
(1) When the valve is opened, the valve body should withstand the internal pressure test twice the working pressure value of the valve;
(2) When the valve is closed, both sides bear 1.1 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.
Fifth, the internal and external anti-corrosion of the soft seal gate valve
5.1 Inside and outside the valve body (including the variable speed transmission box), first of all, shot blasting, sand removal and rust removal should be carried out, and the powdered non-toxic epoxy resin should be electrostatically sprayed, with a thickness of more than 0.3mm. When it is difficult to electrostatically spray non-toxic epoxy resin on extra-large valves, similar non-toxic epoxy paint should also be brushed and sprayed.
5.2 The inside of the valve body and all parts of the valve plate are required to be fully anti-corrosion, on the one hand, it will not rust when soaked in water, and there will be no electrochemical corrosion between the two metals; Second, the surface is smooth, so that the resistance to water is reduced.
5.3 The hygienic requirements of epoxy resin or paint for anti-corrosion in the valve body shall have a test report from the corresponding authority. The chemical and physical properties should also meet the relevant requirements.
Post time: Nov-09-2024
