Pressure control

This post was last edited by Xiaoyao Tenglong on May 9, 2020, at 16:23. Generally speaking, this issue needs to be discussed on a case-by-case basis. The control instructions are usually provided by the process engineering team; instruments are designed with control schemes based on these instructions. The number of control loops is determined according to the specifications provided by the process engineering team. If process control requires it, set up split-range control; split-range control is generally used in situations that involve a lot of sequential operations, thereby reducing the need for manual intervention ； In the case of a discontinuous process, zoning control is generally not employed; manual nitrogen addition (adding nitrogen at specific times) can be considered instead. If your two diagrams represent the same point under the same manufacturing process, and you want to know why some designs include a stage separation while others do not, it’s purely a matter of preference on the part of the automation specialists~! Or it’s just that the owners have different requirements. Some property owners find it troublesome to use the automatic nitrogen replenishment function; they just prefer to add nitrogen manually. Appendix: I noticed that on the combined pipe of the two pipelines in your first diagram, there is a shut-off valve. Can that valve also be used to control the operating range of the split system? If the valve is closed, the split system becomes less useful; it serves to prevent operators from opening both valves at the same time, thereby avoiding waste. Please ask an expert to take a look for you~~ @feng*aosa

This post was last edited by feng*aosa on 2020-5-11 at 18:04. It is necessary to refer to the process or control instructions to determine this, as already clearly explained in the second reply. @Xiaoyao Tenglong Here is a reason given for the arrangement, for reference only. I hope this is helpful: The purpose of staged control is to apply different process procedures to various states of the same controlled parameter ； 　　Regarding the first diagram, when the pressure is high, air is removed using a vacuum pump; when the pressure is low, nitrogen is added (to prevent the container from collapsing?) ） ； 　　This solution is characterized by precision (fixed-value control accuracy), simplicity (compared to program control), and reliability (preventing the operator from failing to replenish air in a timely manner). 　　But this system has a flaw: under certain conditions, it repeatedly fills the air, only for the newly added air to be drawn out again immediately. It not only wastes nitrogen but also increases the system’s energy consumption. Therefore, whether to allow the controlled parameters to deviate (with the pressure ratio being slightly lower for a considerable period of time) needs to be evaluated and considered. 　　The scheme shown in the second diagram can be used when frequent inflation is not required, or when there are other measures to maintain pressure (such as supplying air through a breather valve, with the storage tank being connected to the tank shown in the first diagram).

This falls within the scope of considerations for process design. It’s not possible to see where the PT settings are in these two diagrams; the PT points represent the control points in the manufacturing process. Please note that valve 1# is of the FC type, while valve 2# is of the FO type, which indicates that the subsequent processes may differ. The pressure control scheme for the vacuum system should be checked. Personal guess: 1# PT is set on the device to maintain its pressure. 2# PT is installed at the inlet of the vacuum pump; the addition of N2 is likely intended to reduce the O2 partial pressure in the process gas, with HV being used instead of a two-stage system.