The image below shows a common technique for working on valves in the petroleum industry. A secondary valve 2 is closed and allows servicing of Valve 3.
My question is about the blue area. What is the pressure in this area after the valve has been closed? Does it stay at 10,000 PSI? I opened Valve 3 after some time and some liquid spewed out at a safe velocity. I was told by a technician that the pressure trapped in the blue area is safe, and that it will diminish even further if you allow it to sit for more time. I though that pressure could be contained for a reasonable amount of time in such a setting. I thought that we rely on the ability to contain pressure in storage tanks, for example. I thought that storage of something pressurized would be possible in a valve setting like this. The technician said it is not possible and that he knows first hand from experience. Is this technician wrong? Where does the pressure go?
I have reasoned that it is related to energy, and I have come up with a similar thought experiment to explain this phenomenon. I have a pipe with closed ends and many springs pushed together in series contained within the pipe. I also have a device similar to the blade-like one a magician uses when he does the magic trick to cut off people's limbs in a box. I use a device like this and slide it into the pipe and I isolate only the last spring in the pipe. When I open the end of the pipe, only one spring comes out with limited energy. If I had opened the pipe without using the blade-like isolation device, then many springs would have sprung out with incredible energy. Is this a sound comparison and understanding of the concept?