Custom water maker troubleshooting

[Les Noble]

Tapping the boating brain trust once again. During fit-out, I was up to my neck in other issues and had a brainiac friend design and build a water maker. It did work despite using a pressure washer in the backyard weeds and harbor freight motor, I just didn't trust it in crossing an ocean. While in Ft Lauderdale, upgraded components and some hoses through Seawater Pro. Familiar scenario?
The new system works after fixing a few leaks. However, there are a couple problems I am trying to figure out.

1) Bubbles in flow meter. The bead in the flow meter wasn't rising and bubbles were coming from the vessels. I filled a gallon milk jug which took 2 minutes. 1/2 GPM which is 30 GPH. The meters minimum flow is .5 GPM, so wrong meter. The question is, are the bubbles bad. Does that mean air in the membranes.

2) Water level drops in filters when boost pump is turned off. In initial startup, boost pump is run to purge air. There always seems (6 times?) to be a few bubbles dancing at the top of the filters, even sea strainer. The sea strainer is a vacuum whereas the filters are pressurized. Sea strainer is suspect as air leak. Or is this normal? When the burst pump is turned off, the water level drops in the filters. Its an open system with the seacock open, but where is the air coming from to replace the water? Open system meaning low pressure pump pushes water to the brine overboard, so it should also go the other way. A am assuming the high pressure pump is flow through both ways. In all this I don't hear hissing or leaks. It is a tight fit and can't get my ear near everything. The plumbing is PVC taped threads and push-to-fit (PTF) fittings.

3) PTF at boost pump output bursts when switching product water from test to tanks (twice so far). Once the valves are switched it pops the tube out of the PTF. The hose is seated as I mark them to make sure. The boost pump is adjustable and running at 15 PSI.
I had run across the pressure calculation based on the pump, but not finding it now. I restart the process and decrease to 10+ PSI and seems to work.
Would the flow meter add some resistance?
There is also the PH filter as it is an aluminum sailboat that might be adding resistance, however I sandblasted and potable painted the tanks. This might be a boondoggle as my amazon PH meter failed the calibration and it takes a half minute to read and never seems to settle down.

System drawing (no Coreldraw solution for Linux) attached if gods allow.

Any input appreciated.
Greg
SV Les Noble

[Lepke]

The high pressure pump suction is drawing in air from somewhere before the HP pump. If your filter housings have a button on top to release air, suction from the hp pump can pull the buttons down and draw in air if the water flow and pressure within the filter housings isn't high enough.
There is no reason to tie in your boat water system into the watermaker. It can just lead to contamination problems. Don't use water with any chlorine in it for flushing the membrane.
Your membranes are rated for output at 77°F. Colder input water means lower output, higher temp input water means more flow. See table. If you exceed the rated flow you could tear the membrane. The maximum pressure difference within the membrane housing is 50psi. Until you learn your membrane, put a pressure gauge on each side of the membrane or keep your flow rate at the rating adjusted for sea water temperature.