Seeking help with a minor issue regarding the nitrogen purge device

I’m not sure which device it is; let me first describe what I’ve experienced with my own equipment. The DMTO unit is used for measuring pressure, density, and volume of the process medium. 1. The pressure of the purge gas is higher than the pressure inside the equipment, but there are check valves and flow control orifice plates at the outlet of the purge gas. 2. It definitely displays the pressure inside the tank. 3. The purpose of purging is to prevent the process medium from clogging or coming into direct contact with the transmitter; if the pressure tap pipe gets blocked, it’s possible to close the main process valve and open the secondary valve of the instrument in order to purge the pressure tap pipe. 4. The purging system is always in operation

1. Must the outlet pressure of the purging device be higher than the pressure inside the tank in order to carry out proper purging? Answer: It must be. 2. When in normal operation, does the pressure reading on the gauge at the purge outlet indicate the purge outlet pressure, or does it indicate the pressure inside the tank (this question arises because the gas supply pipe and the pressure sensing pipe are connected)? Answer: According to your diagram, the pressure gauge shows the purging pressure. Equipment pressure = gauge reading – purge line pressure drop (the pressure loss in the lines through which the purge gas flows). Therefore, it is better to control the flow rate to be lower, especially for differential pressure measurement. 3. The outlet of the air supply pipe for the purging device is connected near the valve; if the transmitter’s readings are inaccurate, can’t the section downstream of the pressure tap be purged in reverse? Answer: The purging pipeline has pushed the medium \"back\", achieving the desired goal; the pressure guide pipe can be considered \"clean\", as there is no flow of medium inside it and no pressure drop. There are also those that inject backflow from the transmitter valve assembly, which facilitates maintenance. According to 2, the reading deviation will be larger, but transmitter migration can be performed. Purging = isolated diaphragm cell, except that the isolation fluid moves slowly.

As the title suggests, for the pipes of purging equipment, some require manual cleaning, some need to be cleaned using high-speed air currents (under vibration), and others are purged by explosion. The conditions for purging cannot be determined by pressure alone; it involves a comprehensive consideration of pressure, flow rate, velocity, and pipe diameter. Furthermore, even with maximum pressure applied to your diagram, it is not possible to ensure a thorough cleaning of the container; the purpose of purging is to remove particulate impurities such as mechanical debris, welding slag, rust, and other similar particles from the pipes. There is also a situation where, due to process requirements, it is necessary to remove air or other substances from the equipment pipelines that are involved in chemical reactions; this process is referred to as \"purging\", but it should actually be called \"replacement\". Inert gases such as nitrogen, as well as steam, are commonly used. Purging refers to physical cleaning ； Substitution is a chemical purification process that requires specific elemental content levels. The use of various methods is determined based on production needs, for reference.

Sometimes the pressure drop is very small; if it is large, it indicates that the pipeline is not unobstructed. If a differential pressure gauge is connected, the pressure drops on the two sides can cancel each other out.