Due to the wide variety of valve specifications, such as general-purpose valves have gate valves, globe valves, check valves, ball valves, butterfly valves, hydraulic control valves; industrial valves have solenoid valves, regulating valves, pressure reducing valves, high-temperature and high-pressure valves, low-temperature valves and other special valves, are used in various areas of the national economy, the use of the occasion is very different, such as high temperature and high pressure, low-temperature deep cold, flammable and explosive, highly toxic, strong corrosive media and other working conditions. The material of the valve has put forward harsh requirements.
In addition to cast iron, carbon steel, alloy structural steel, but also a large number of CrNi stainless steel, CrMoAl nitriding steel, CrMoV heat-resistant steel, CrMnN acid-resistant steel, precipitation hardening steel, duplex stainless steel, low-temperature steel, titanium alloy, Monel alloy, Inconel alloy, Hastelloy and G0CrW carbide, etc.. The casting, welding and processing properties of these high-alloy materials are very poor, which makes the manufacturing process very difficult. Coupled with the fact that most of these materials are high alloy, high strength, high hardness precious materials, there are many difficulties in the selection, preparation and procurement from the materials. Some materials are difficult to procure supply due to the small amount of use.
Valve body (casting, sealing surface overlay welding)
Casting procurement (according to the standard) → into the factory inspection (according to the standard) → surfacing groove → ultrasonic flaw detection (according to the drawings) → surfacing and post-welding heat treatment → finishing → grinding sealing surface? Seal surface hardness inspection, coloring flaw detection.
Raw material procurement (according to the standard) → into the factory inspection (according to the standard) → production of rough (round steel or forgings, according to the drawing process requirements) and sampling for the necessary inspection → rough machining → finishing → spectral inspection.
Pick up parts → cleaning, cleaning → rough assembly (according to the drawings) → hydraulic test (according to the drawings, process) → after passing, disassembly, wipe clean → final assembly → commissioning with electric installation or actuator (for electric valves) → paint packaging → shipping.
In understanding the steps to master the selection of valves, should further understand the basis for the selection of valves.
characteristics: flow resistance, discharge capacity, flow characteristics, sealing grade, etc.
If the valve is to be used for control purposes, the following additional parameters must be determined: method of operation, maximum and minimum flow requirements, pressure drop for normal flow, pressure drop when closed, and maximum and minimum inlet pressure of the valve.
Based on the above basis and steps for selecting valves, a reasonable and correct selection of valves must also be based on a detailed understanding of the internal structure of the various types of valves so that the right choice can be made for the preferred valve.
The final control of the pipeline is the valve. Valve opening and closing parts control the way the medium flows in the pipeline, the shape of the valve flow channel so that the valve has certain flow characteristics, which must be taken into account when selecting the most suitable valve for installation in the pipeline system.
Pumps and valves are often linked together because of the use of occasions. That is, there are pumps where there are generally valves, and some places often need pumps. They are both used in places where liquids are transported. Of course, valves are also used for gases. Vacuum pumps are also associated with gases.
Pump valve definition: valves not used for pumps or valves with a pump role.
Casting is the material in the mold as a whole pouring molding, it has a uniform stress distribution, there is no restriction on the direction of pressure. Forgings are pressed by the same direction of force, it has internal stress directional, and can only withstand directional pressure. The same material, the same wall thickness of castings and forgings, in strength and crystal phase structure, forgings are better than castings. For the globe valve, the same poundage, the same material castings globe valve wall thickness to thicker than forgings. Its pressure strength is equal to that of forgings. Casting requirements for the casting process is relatively high, the most important feature is that you can make a more complex shape, the body structure of the globe valve and the flow channel are irregular, casting can be a one-time molding, as long as the process is good, you can cast the body of the large diameter globe valve. For example, the United States VTON forged globe valve, imported forged ball valve, imported forged globe valve caliber can be up to 20 inches. Forgings are better dense, but for too complex flow and shape can not be formed at once, often need to be modular, separate forging and then welded together, so the size of the forgings are somewhat limited.
Forgings are often not machined to produce complex, streamlined runners. The runners are machined by turning and form many sharp corners inside the transition, which can easily cause uneven stress and cracking. At the same time, the modular welded design, forged globe valve seat bore is relatively fixed, in some globe valve size, its bore is small, affecting the flow capacity. This results in increased flow resistance of the globe valve and reduced efficiency of the entire system.
Due to the limitations of the forging process in large size globe valve, and to save costs, many manufacturers usually use the center part of the valve body castings, forgings at both ends of the structure. Whether castings, forgings. In the processing, there are possible product defects. The main defects of castings are in trachoma, bubbles, etc.; the main defects of forgings are in large grains, cold hardening phenomenon, cracks, cracks, etc. In order to obtain qualified product quality, the corresponding castings need heat treatment to eliminate the stress in the casting process, while using X-ray, magnetic particle flaw detection, penetration inspection and other detection means. For forgings, this requires strict heat treatment of the weld and the corresponding inspection methods to ensure. Forgings often require ultrasonic inspection. In addition, it should be mentioned that the welding process is very strict, the welding engineer’s qualification is the key.
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