Yesterday my mechanically inept boss ran a DIY water vacuum system with the outlet valve closed and blew apart a piping connection. The connection was a rubber sleeve holding 2 pieces of PVC piping together with hose clamps.
I suggested "instead of using that mickey mouse connection we should replace all the piping with threaded steel pipe"
His reply. "No absolutely not, the pressure will blow those pipes apart and with steel pipes, that would kill someone. Even if it doesn't explode, the pump would just turn the water in the reservoir to steam and blow the pump apart. The PVC is a safety mechanism. I know it would explode because I've seen it happen!"
It's a 1/2 hp motor with a plastic impeller and was never meant to be run with the outlet valve closed at all...
This man has the power to tell me what to do, and there's no reasoning with him.