I meant to say this earlier: With a nearly full water tank, the resting pressure at the Secret Lair’s sink is 18.5 PSI.
Flow pressure is about 14 and a quarter. Now the trick will be to watch the tank level over the next few weeks, with the well pump turned off, and see if the resting pressure drops at all with the tank level. I harbor doubts but Big Brother thinks it will and if we disagree on a science fact he’s the one to bet on.
I could cut through this by opening a valve and mostly emptying the tank, but wasting water is a sin. Darwin spank. So I’m going to let the experiment take its sweet time.
1ft of water is 0.4335psi. Assuming a 5ft tall tank empty should be ~16.4psi
So dividing 18.5 by .4335 implies that the surface of the water in the storage tank is presently 42.675 feet above your sink. Does that sound right?
According to a GPS I borrowed many years ago it should be closer to 50 feet, but I really don’t know for sure.
Your brother is correct. Think of the tank as a huge piston. The weight of the water which generates roughly 14 PSI per 33 feet of column height. As the water level drops, the pressure exerted by the tank will diminish a bit. My rough calculation was that if the tank is 12 feet tall and full, when it nears bottom, you should see about a 4 PSi drop in pressure from the full reading. The pipe is probably about 1 inch square in surface area so it will not be major factor even if 40′ drop in the grand scheme of things. Let’s see who comes closer to the target 😉