Double-plate gate valve

Last year, when the installation was being built. I have also struggled with this issue. I’ve also communicated with the manufacturers. Double-disc gate valves provide good sealing in cold areas. The pressure relief hole is used to release the vaporized fluid between the gate plates. According to the manufacturer. The pressure relief hole should face the side that is safe when it is closed. Actually, it is during the construction phase. The workers could not tell which side was safe. But it’s all marked on the PID diagram. But there will inevitably be discrepancies. Actually, upon thinking about it, there’s no big problem. If a control valve needs to be removed. If the pressure relief holes on the front and rear valves face the control valve. When releasing pressure between the two valves. The pressure on the gate plate has also been relieved. If it faces the material side. The pressure between the gate plates is the same as on the material side. The pipeline is not overpressured. The gate plate will not experience overpressure either. There’s no problem.

I want to know if the stop valves used on the pipelines in the cold zone (the pipelines carrying ethylene) have pressure relief holes

The specific situation is unclear. In other two-valve systems, there is a certain scenario; it’s not known whether this applies here as well. Is the medium between the valves a liquefied gas at low temperatures? If the two gate plates are closed, this area becomes completely airtight, and the force resulting from the expansion of the liquefied gas as its temperature rises acts directly on the gate plates. This volume expansion force is different from the saturation pressure; it is much greater than the saturation pressure. So, a pressure relief hole needs to be installed.