THE ACCUMULATOR

The accumulator is a most interesting creature. Because of its odd shape, I dropped a circular 3/4 inch piece of plywood into a 5 gallon bucket, screwed some stainless steel strips to the plywood through the bottom to anchor the thing, put the two gallon accumulator in the bucket, and filled the space left with Great Stuff spray foam. Now instead of being a liability to the piping system it becomes an anchoring point for the tubing.
An accumulator stores energy by compressing air. There is an original "charge" of air retained and separated from the water by a membrane. As the pump cycles on it pumps water into the water section of the accumulator, compressing the air on the other side of the membrane. Remember, liquids are for all practical purposes, not compressible, but gases (like air) are. So when the pump reaches its "cut out " pressure point (on mine 45 psi), it has not only pumped water but also stored up some temporary pressure that will add to the time before the pump turns back on at its cut in pressure point - THUS AVOIDING THE ON/OFF "SHORT CYCLING" THAT WEARS OUT PUMPS PREMATURLY.
My 2 gallon accumulator (they are actually sold as thermal expansion tanks for hot water heaters) came from Lowes for $43 dollars. It had an original "charge" of 25 psi. There is a air valve near the bottom of the tank to add or subtract air. (be sure to cut a hole in bucket for access). The charge should be set at a 2 or 3 psi below pump cut in setting. Can't help but challenge you to figure out why!
F is the back of the galley sink faucet. Next the PEX curves around heads for the bath room. The curve wastes little energy, as opposed to a sharp bend. At G there is a "T" that sends cold water to the water heater through a check valve that prevents the hot water from flowing backwards. I took the 6 gallon water heater apart and found it in good condition. I locally got a new 1500 watt, 120 volt heating element (original was 1250w, but 1500w was as close as I could come), as well as a new pressure release valve, both for a total of $25. The pressure release valve blows at 150 psi instead of the original 75psi, but the tank has working pressure with 150 psi on label, as well as tested to 300 psi, so I got what was available. Tested out the water heater and it heated up to my setting of 120 degrees in 1/2 hour. - THAT being an upside of a small tank - even though there isn't a lot of hot water relative to a residence, it does recover fast.
NOW HERE IS A VERY IMPORTANT POINT. You can set the thermostat into scalding range so you mix less hot water with the cold, AND SINCE THE HEATER IS EQUIPED WITH AN ENGINE HEAT EXCHANGER, IT CAN IN THEORY GET TO DANGEROUSLY SCALDING RANGE REGARDLESS OF WHAT YOU SET THE THERMOSTAT AT. THEREFORE YOU NEED A THERMOSTATIC MIXING VALVE FOR THE HOT WATER COMING OUT OF THE WATER HEATER TANK. You set this to the temperature that you want all hot water in the system to be at, and it automatically mixes cold water with the hot to make sure that temperature is achieved, regardless of what the temperature of the water coming out of the water heater is. I have not put this in my system yet, but absolutely intend to. This is a good place to point out that I am self taught in the last few weeks and only offer beginner ideas, NOT PROFESSIONAL ADVICE. Now on to what I learned about PEX systems. I will refer back to the fittings in this photo at H and H'.