May I ask if it is acceptable to use a control valve for nitrogen sealing, a control valve to regulate the pressure of the incoming nitrogen, and a switch valve to regulate the pressure of the outgoing nitrogen?

What is the difference between a control valve and a switch valve? One with a locator, one without. Without a positioner, it operates in either fully open or fully closed mode; if the valve is too small, the discharge volume is insufficient, while if it is too large, the regulation is unstable

As long as you dare to think, anything is possible.

It is best to refer to a diagram for this issue, to facilitate targeted discussion. Since nitrogen sealing is a general term used in various fields, it is most reliable to understand it through diagrams. For reference.

If it is used for nitrogen sealing, a force-operated control valve will suffice

It depends on the relationship between flow and pressure changes. The amount of N2 introduced should match the volume of liquid discharged, and is roughly equal to the discharge flow rate of the pump. The pressure drop across the pressure relief valve is relatively large; when a switch valve that does not experience pressure drop is used, the flow rate of fluid injected is high, which can easily lead to overpressure, especially in small tanks (or tanks with a low discharge flow rate). The displacement of the relief valve should match the volume of liquid being injected, but the pressure drop across the valve is relatively low, so the displacement isn’t very large. In some applications, on-off valves are indeed used, such as for batch processing in tanks. Regarding this topic, in fact, the range of pressure control precision required can be achieved by using valves that can tolerate a certain pressure drop; such valves help to keep the flow rate from becoming too high, allowing for gradual control of the flow rate and thus maintaining the desired pressure control range.

For this, a self-acting pressure control valve with a controller is sufficient now. Install a micro-pressure valve on the outlet. I’ll keep both the inlet and outlet pressures tightly under control. There is no need for you to provide manual signals or make adjustments. Maintain a constant nitrogen pressure in the tank. If there are safety requirements related to the manufacturing process, you need to install several safety valves and vent valves. Compared to control valves with positioners, it can save a significant amount of money.

What type of valve are the micro-pressure valves used in exports?

It is the nitrogen relief valve, a self-acting control valve that regulates the pressure in front of the control valve (the tank pressure).

The choice of valve mainly depends on your process requirements. All the situations mentioned by the original poster apply; for the most economical option, choose a on/off valve, for stability, opt for a control valve, and for the best cost-performance ratio, go with a self-acting valve