Our well water pressure changes when we run the system at the high end such as outside hoses or more than one item at the same time. We had the well pump, pressure tank and pressure switch change about 5 years ago. I had the pressure switch changed which is set for 30 to 50,the pressure tank was at 0 so I fill it to a set point of 27 . Well is about 300 feet deep
When I use the outside hose at full the pressure goes down under the set point to different number even 0 sometimes. The high pressure changes stopping anywere from 30 up to 50. If I run the system very slow like the bathroom sink the pressure switch run correct.

I'm curious as to how your tank pressure (at the valve at the top) managed to get to zero. I'm wondering if the valve is leaking.

At any rate, I would watch my switch as water is being used from the outside faucet. You should hear the valve "click" at 30 (cutting on) and click again at 50 (cutting off) as the points close or open. If that doesn't seem to be the case, then turn off the power and check the points. If they seem corroded, use an emory board or a folded piece of sandpaper to clean them. IF that doesn't seem to help, then take off the switch from the threaded fitting and see if the little pipe leading to the switch is clogged with "crud". If so, then either clean it out or replace it. If it's clean, then you are probably looking at a bad switch. Thankfully, they are cheap... twenty bucks or so.

Hey Vette,
How old is your house and what material are the water pipes made of? Back to you, Tom