Performance specification for Ball valve with pneumatic actuator

Ball valve with pneumatic actuator  is the active control in the industry the most commonly used terminal control element, pneumatic ball valve fluid conditioning activity (medium), set point to compensate the load and makes the control of the process as much as possible to meet the requirements, according to their importance in industrial automation field, the aerodynamic and planning manufacture of ball valve is particularly important, especially some strict harsh conditions, such as temperature, pressure differential, high flow velocity and cavitation etc., will be on from the data structure, manufacturing, etc..
I. selection of pneumatic ball valve data:
1, metal materials; data is the key factor, such as the function of information, creep, thermal expansion rate, oxidation resistance, wear resistance, thermal abrasion and heat treatment temperature, the first is the matters should be paid attention to. Under the condition of high temperature, creep and cracking is one of the most important elements of data damage, especially when carbon steel, long time exposure to the above 425 DEG C, carbide in steel phase may change graphite, and on austenitic stainless steel only when the carbon content exceeds 0.4%, it can be used for more than 528 DEG C. Therefore, in the use of high temperature, should be calculated from the valve body tensile strength, creep, high temperature aging and other parameters. And on the valve parts planning, but also should be attached to thinking about the data in the high temperature hardness, with parts of the thermal expansion coefficient, the guiding components of the thermal hardness difference, elastic deformation, plastic deformation and so on. In planning, the corresponding safety factor and reliability coefficient should be given to prevent damage caused by multiple elements. And to understand the high temperature creep data rate, to choose the suitable stress, the total creep data in the normal use life range expansion to the normal use of the onset of cracking or to micro deformation and does not affect the orientation of parts.
To prevent pneumatic ball valve parts (spool, valve seat) surface wear, erosion and cavitation, high temperature circumstances to consider the data of thermal hardness, to prevent metal hardness change. Under a high pressure difference, most of the energy concentrated in the fluid valve parts are released, there may be overload on the inside part of the valve, and high temperature, mechanical function of most data poor data become soft, greatly affected the valve parts using life. Therefore, proper data should be selected to extend the service life of the valve. In addition, we should consider the influence of high temperature aging on the physical function of data, such as the change of resistance and intergranular corrosion. When the temperature reaches or exceeds the heat treatment temperature, valve parts will attack the annealing, the hardness decreased a level of doubt, in order to prevent the material hardness change, the maximum temperature limit selection is necessary in a safe range. But as the medium, under the condition of high temperature, the activity of the molecules is relatively active, usually with some corrosive medium on the valve body and the valve internals may bring serious corrosion damage of metal materials, metal ions with medium into the internal state of high speed, the data characteristics change, such as the expansion of large, crystal between corrosion, therefore, the material selection, in addition to price, should also be the failure of many elements under the attack of thinking.
Under the condition of high pressure difference and high flow rate, even if the temperature is normal temperature, the characteristics of the data should be evaluated so that the data can be satisfied with the working condition. Generally speaking, under normal temperature, when the pressure exceeds 15bar, the valve spool and valve seat materials from 316 to stellite alloy welding or higher request on the alloy, weak corrosive medium, can choose 420QT (quenching and tempering), 440QT etc.. High pressure and high flow rate will bring severe erosion or cavitation damage to the valve parts, this data is very large, therefore, the valve body and valve parts of the data request is very high, a spool should consider the use of stainless steel (HRC70) surface nitriding treatment, which has strong erosion resistance, improve the flow valve the precision and service life. The antioxidant capacity of data at high temperatures is also a very important parameter. In the change of the temperature cycle, the data chosen should be prevented from repeated oxidation of the surface of the detected material and the occurrence of an oxide skin. Under normal circumstances, austenitic stainless steel, carbide and special alloy materials have better high-temperature stability, can be based on different high temperature conditions to select appropriate data.
2 non-metallic materials
Non metallic materials are usually unable to accept the high temperature (above 300 C), but the flexible graphite can accept high temperature above 700 DEG C, and high temperature conditions, both static sealing is dynamic seal, usually can choose flexible graphite or composite materials, but it should be noted that the friction coefficient increases.
Two. Construction of pneumatic ball valve parts and selection of thermal conductivity:
High temperature and high pressure differential pneumatic ball valve planning, it is necessary to carefully consider the role of different parts of the expansion of the valve action. When the high temperature medium flow through the valve, because the valve body line coefficient is usually less than the seat of the line swell swell coefficient, so the radial body constraint seat seat only to swell, swell the diameter, under high temperature, valve core and valve seat of the gap is smaller than the valve gap operation planning standards at room temperature, the formation of valve stuck. Spool and guide sleeve will attack the same phenomenon. Therefore, the use of the valve at high temperature, room temperature standard valve clearance plan (including the valve, the valve seat; the guide sleeve and the stem between) should be added, so the high temperature operation will not attack blocking phenomenon. Therefore the planning gap is very important, because the data scale and the temperature difference of the parameters such as admit that it is very important for planners, now, can get the corresponding number from the "ASME boiler and pressure vessel standard II D" in the textual function data