NEW PEX PRESSURIZED FRESH WATER SYSTEM

So having been at the rebuild from the deadwood up for eight years, you would expect I gutted the boat systems just because they were in the way, not to mention that I was clueless about what was going on. So with launch date the week after the first warm weather in March, and with the hull done, I am focusing on designing and building systems. (not that this system isn't an almost identical one from BOAT USA) - however, since I studied it hard I understand the components........pride goeth before the fall) I chose PEX for a lot of reasons.... google and find out. There are abundant fitting that allow you move from PEX to copper, or PVC. But let me say this.......100 feet of PEX costs $28 dollars.
A) These two metal pieces are a standard example of transitioning from a pipe fitting to a PEX fitting, The pipe 90 is or can be fitted on the straight pipe coming out of both the Newporter water tanks. The screw on PEX fitting for 1/2 " PEX costs between 2 and three dollars.
B) a couple of PEX shut off valves ($8 a piece) that allows me to choose my tank.
C) Starting at the shut off valves (B) I soldered up a little copper "manifold" (joke, but seriously, if you google how to PEX there is a free industry PDF that in 117 pages tells all......and one section talks about the 3 styles of PEX systems: trunk and branch, parallel, and zone. To make a long story short, with only a galley sink, shower, and bathroom sink, the trunk and branch was for me). So The main function is to choose which tank (fwd or aft) I am drawing from, as well be able to really fasten down this central part of the system with copper "brackets".
D) this "branch" off the main "trunk" has three possible uses: 1) to drain the main tanks 2) to put a hose in a bucket with RV winterizing fluid 3) to set up a separate line for a manual pump at the galley sink in case battery power gets scarce. Obviously all components are not there but you can see where I am going.
E) is a sure flow Par Max 4 diaphragm pump with a pressure switch set at 45 PSI. This particular pump came with the boat, and was manufactured in 2005. Be sure to study up on fusing and wiring size - there are some subtleties.
F) is a branch to drain the piping system if you do not want to pump RV antifreeze into the system. I have not thought through the draining process, but assume you shut off tanks and open everything, including this drain which will be below all fittings. OBVIOUSLY THE PEX SECTIONS OF PIPE DO NOT REPRESENT ACTUAL LENGTHS.
G) Now we get to the Accumulator! Good gosh I worked to get this all straight - when in fact is simple if someone would explain it. IF the waterline is opened, for instance at the sink, without an accumulator, the pump almost immediately cycles on, even for a sip of water. This makes a lot of noise and wears the pump out prematurely. (the pump comes on at, for example, 32 PSI and then pumps until 45 PSI is reached. The time before the pump comes on depends on the volume of water under pressure in the system (I think). The function of the accumulator is to add extra volume (air and water) under pressure so that the cut in pressure of the pump is not reached as fast, ie once the pump comes on it not only pumps the water, but it also does work on the water and air in the accumulator to store up energy. Then when the pump reaches the cut off value, there is extra energy stored in the system.
I worked with three different designs from the internet before I found a post that said just go to Lowes and spend $43 dollars for on that has the air and water separated by a membrane, instead of homemade with no membrane that has to be recharged on a regular basis. So now go to the next photo to continue.