Water Pressure Fluctuations

First of all: 1/2 inch for a main is ludicrous.

Second: what is the incoming pressure?

Third: Well or City?

Fourth: How high is second floor above incoming line?

Sounds like a generally poorly designed system in dire need of major upgrade to me, but impossible to help due to lack of info.

Main runs needed to be at least 3/4.
3/4 has close to double the flow of 1/2".
Also is there a pressure tank?

Old style gate valves can also have issues. There prone to not being able to shut off fully, stems can snap off inside the valve so the gate can not move.

Has Cistern been cleaned? Check my previous post re Cistern. Basically, You need bigger main lines.

Thanks - That's what I figured.

I planned on upgrading the plumbing it seems pretty messy at this point. Just a few quick questions;

1. Would it be best to run 3/4" trunks or 1" trunks for 1/2" branch off? Or 3/4" to each fixture then reduced to 1/2" to go into the fixture?

2. For optimum hot water distribution, is it best to run 3/4" from main trunk into the hot water tank, then 3/4" hot trunk out to 1/2" branches? What about a manifold for the hot water supply? Better service/pressure?

3. When running pex to fixtures, I have seen that the pex is fixed to copper lines for the last 1-2ft before it is connected to the fixture. Is this code? I would assume it is for the waterheater...

Thanks!

Copper pipe is not immune from arteriosclerosis after decades of use.

This can cause drastic drops in pressure when more than one sink/shower/etc. is in use at the same time.

You use one of these where it comes out of the wall so the valve is not just hanging from a flexable piece of tubing.
http://www.pexsupply.com/Viega-44227-Zero-Lead-1-2-PEX-Crimp-x-1-2-Copper-Stub-Out-Elbow-w-Plate

Also you can then just use a standard 3/8 X 1/2 compression stop.