Selection of steam pneumatic control valves – Flow closure
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According to the structural diagram of the control valve, during installation, is it required that the steam control valve have steam entering from the high side and exiting from the low side? The diagram shows steam entering from the right and exiting from the left; thus, conventional control valves are designed to be flow-blocking by default. Therefore, if it is maintained that liquid flows in at a high level and out at a low level, while gas flows in at a low level and out at a high level, with the valve core’s stroke located in the upper part of the valve chamber, it can be basically determined that the liquid flow will occur when the valve is open, and the gas flow will occur when the valve is closed. If the principle of fluid inflow and outflow is not adhered to, or if the stroke of the valve element is designed at the lower part of the valve chamber, are there any other alternatives? I’m not sure if I understand correctly; please let me know if you understand, dear friend.
The selection and installation of steam pneumatic control valves involve the physical properties of the fluid and process requirements, and the choice must be made based on specific circumstances. Generally, the inlet and outlet directions of a control valve affect its proper operation. Here are some general principles and explanations: 1. High in, low out principle: For liquid fluids, the high in, low out approach is generally used; this helps maintain stable flow within the valve, reduces noise and vibration, and prevents bubbles from entering the system. This is also a standard practice. 2. Spool travel: The spool’s travel is related to the inlet and outlet directions; typically, the spool is used to control liquids in the upper part of the valve chamber, while it is used to control gases in the lower part. This is because gases and liquids have different physical properties, requiring different control methods. 3. Principle of gas and liquid inflow and outflow: It is a common principle for liquids to flow in from a higher level and out from a lower level, and for gases to flow in from a lower level and out from a higher level, but this is not absolute. The specific details may be influenced by factors such as process requirements, pipeline layout, control systems, and fluid properties. 4. Valve core position: The position of the valve core is usually determined based on the properties of the fluid and the requirements of the system. If the principle of high inlet and low outlet is not adhered to, other methods may need to be employed, such as changing the position of the valve core or using special designs to accommodate special situations. In summary, the selection and installation of steam pneumatic control valves require consideration of various factors, including fluid properties, process requirements, system layout, and control strategies. The best approach is to conduct an assessment based on the specific circumstances; it may be necessary to consult a professional engineer to ensure that the selection and installation meet the requirements. .
The explanation was excellent! Well-organized! !
1. For liquid fluids, is it usually high in and low out? Is it like this?
The explanation is very comprehensive: victory:
Why do I feel like it’s always going down and coming up?:sleepy:
. Regardless of whether it is high in and low out or low in and high out, the control valve should be used according to the flow direction indicated on the valve body； Control valves come in six variations: direct-acting vs. reverse-acting, normal installation vs. inverted installation, flow-open vs. flow-close. However, for a specific product, its optimal design is generally already determined; any changes made to it require evaluation to determine whether their consequences are acceptable. In particular, the actuation thrust related to flow opening and flow closing, as well as mechanical shock (response to water hammer effects), vary greatly; therefore, the mode of use should not be changed arbitrarily. Flow open and flow closed, positive and negative actions, as well as normal and reversed orientation.
The optimal structure has basically been determined. Valves manufactured by factories are certainly designed and tested thoroughly. So there must be certain principles behind the design of steam control valves, right? And they must differ from control valves used for ordinary liquids as well, right? Actually, everyone just wants to know why it was designed this way It’s not that I want to change the way of using it arbitrarily; I couldn’t find the information I needed, so I came to the forum to ask if anyone could provide an answer.
In boilers with medium and low pressures, fluid generally flows in from the lower side and out from the higher side; when closed, the sealing surfaces are not subject to liquid corrosion； At high pressures, a high inlet and low outlet configuration is used; the medium pressure presses against the sealing surface, which aids in sealing.
Steam control valves, especially saturated steam control valves, often present selection difficulties during selection, as the working fluid is frequently at the phase transition critical point. For saturated steam control valves, the calculations are not very different from those for gases. However, in terms of design, various approaches are employed to counteract \"cavitation\"; many designs that should be effective in theory can yield very different results when implemented by different manufacturers. Therefore, when making a selection, the focus should be on the brand and the manufacturer’s performance.
You can have the engineers at Fisher/Masoneilan do the calculations for you. Their calculation software is truly powerful; no selection software from domestic valve manufacturers can compare to it.