What Went Wrong

[justwater]

swapping from the 1/2 to 3/4 pump shouldnt matter as much as if you had changed from a 3/4 pump to a 1/2...

[Zoomboy]

Thanks all of you. I am scheduled for Wednesday for replacement of the "guts". I know, this is gambling in small way, as I could still land with drilling completely new well.
Need your opinion on my thoughts. When I shut the power going to the pump before leaving house for work, after coming back pressure drops almost to zero. I am sure that I do not have any leak and only device using water during my absence could be rather sizable RO system. But when I also shut main on water pipe, pressure stays at same level when I leave.
Would be this an indication that my pipe (that one 1" running inside 2" pipe) is solid without any breakage? From previous post you can read that I've tried to pull it out from the wall. However, I didn't use excessive force and stopped after short while.

[Zoomboy]

Quick update. The "well-man" did honest effort to just replace components of the old well. Unfortunately, the age and consequent rust buildup caused break-up of inner parts, rendering removing old stuff impossible and frankly, impractical.
We are drilling the NEW WELL!

[Porky]

From your photos it looks like you don't have a jet assembly at all. You need a Meyers SW50A - Convertible Jet Assembly. Without this jet assembly you'l never get more than 30 psi. Pumps don't build pressure, Jets build the pressure. Since you now have a 3/4 hp pump you may need a "SW75A - Convertable Jet Assembly". The noise that you are hearing is probably cavitation (high suction due to no jet assembly. The back pressure valve as you called it is to hold at least 22 lbs of back pressure on the pump. It's not necessary once the pump is primed. I wouldn't be concerned with reinstalling it at this point, It may just be a little harder and take a little longer to prime the first time. You are better off with the pump running on 230 volts.