See answers below.
Situation : Drawing from the lake on 1 1/2" poly, 1/2 hp jet pump (don't know GPM) about 20' above surface, small (8 gallon?) pressure tank set 65/40 pushing uphill to cottage 50' away 20'higher on 1" poly, basic "T" then another 50' to the bunkie with 15' higher. each building has WC, shower, sink, kitchen sink. Water pressure is okay for one fixture use, poor at best if multiple fixtures (or one building flushes when you are in the shower in the other) more than that and water basically stops.
I am looking at replacing the jet with a submersible.
1. What GPM do I need? (I'm thinking 10 is lots based on fixtures).
1/2 HP sub will give more flow than a 1/2 HP jet. Use a 3/4 HP 10 GPM sub, and you will have plenty of pressure.
2. Does the pressure tank belong in front of the "T"?
Do I need a bigger pressure tank?
Yes or a Cycle Stop Valve with the tank you have.
Should I move pressure tank up to the first cottage?
Pressure tank needs to stay with the pressure switch. Don't move one without the other. Either place should be fine.
Should I have 2 pressure tanks, one under each building?
If so, is there creative valve use that would allow me to have 2 tanks and one pressure switch?
or how would I wire 2 pressure switches?
3. Should I increase the line size?
No, should be fine.
If so, where?
Between the lake and the pressure tank, or
Between pressure tank and "T" where it splits to the bunkie?
Oh ya - and I want it to be easy to drain for winterizing...
Put a brass bleeder orifice under water after the pump. Use no other check valves than the one on the pump itself.
Thanks for your wisdom...