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Note the details of the selection of the regulating valve

Select the attention detail of the regulating valve
Only after fully understanding the structure, use characteristics, process requirements, and work requirements of the regulating valve, the combination of the regulating valve and the process can be satisfactorily obtained. When there is a problem with the regulating valve, in addition to considering the problem of the regulating valve itself, it is also necessary to see if there is an error in the selection.
How to choose a regulating valve is a key issue. From the valve structure, summed up need to consider and pay attention to the following points:
(1) The single-sealing type regulating valve is suitable for high sealing requirements and cutting occasions, but the general unbalanced force (ft) is large, and the allowable pressure difference is small, which is not suitable for occasions where the pressure difference is large.
(2) Double seal type regulating valve, generally balanced structure, suitable for occasions where large differential pressure is allowed, but the two sealing faces cannot be contacted at the same time, and one seal is more than one seal, which is not suitable for occasions with high sealing requirements.
(3) The single-sealed balanced structure overcomes the above shortcomings of (1) and (2), and is suitable for occasions with strict sealing and large pressure difference. However, the general balanced sealing member is non-metallic, so it can only be used for normal temperature and is not suitable for high temperature. occasion.
(4) General straight-through ball valves are not suitable for high viscosity, suspension, and solid particles. From the performance requirements, it is necessary to consider and pay attention to the following problems: When considering the sealing performance, a single seal type regulating valve and a rotary type regulating valve (non-ordinary butterfly valve) can be considered in the structure; a soft seal can be considered on the throttle member Or a pile of Stella alloys; flow closure can be considered in the flow direction; positioners, relays, etc. can be considered in the attachment to increase the output force; when considering the differential pressure performance, the structure is considered double seal Class regulating valve; consider flow closure in flow direction; select small Fr, with accessories to increase output force. Angle valve and rotary type regulating valve can be considered from the "self-cleaning" performance; flow closing is considered in the flow direction. From the perspective of service life, special materials resistant to cavitation and erosion (such as 6VC1) are selected; the flow is mainly selected in the flow direction to prevent small opening work.
(5) From the stability point of view, choose a valve with small ft change; choose large Fr (spring tension) to increase stiffness; in flow direction, ds is less than dg, optional flow type (ds is stem diameter, dg is valve seat) Diameter); prevent small opening work; use logarithmic characteristics in flow characteristics.
(6) From the perspective of reliability, pneumatic actuators are much better than electric actuators. When possible, pneumatic actuators should be used as much as possible; to prevent and reduce leakage, graphite packing and special gaskets (such as metal seals) can be considered. Pads, stainless steel graphite wound gaskets, etc.); comprehensive resistance to corrosion, pressure, throttle life, moisture resistance, etc. should also be considered.
(7) From the economic point of view, it should be considered that the structure is simple, the maintenance is convenient, the price is low, the service life is long (the price is related to the life), the capacity of the valve is large, and the linear flow characteristics are. In summary. There are also advantages and disadvantages under the same conditions, so we should also seize the contradiction. Take appropriate measures to prevent and reduce side effects.

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