An Expert Relief Valve Overview 

What are you talking about? Test stands for valves or the valves themselves?

Why the hell would you want to do that 😂

😂😂😂

I've worked on quite a few pilot valves and none of them are affected by downstream pressure. The pilot essentially works like a pressure switch an a solenoid. When the process pressure pressure reaches the set pressure it vents the top of the main to atmosphere which allows the main piston to open relieving the pressure. The pilot itself has no connection to downstream pressure so it can accurately open the main without any interference from changes on the vent side. You might see the diagram and think the downstream pressure could be connected to the top of the main piston but if you saw one in person the main piston is in a sealed tube with seals on the outside that prevent leakage from the downstream pressure to the pressure that keeps it sealed.