The pressure sys. is designed with the check valve at the
pump. the filter {should be}, on the inlet side of the
pump between the tank and the
pump. Advent #1, I put together a 4" x 24" clear plastic pipe with caps on both ends and a 1/2" inlet fitting near one end and a 1/2" fitting mid-way along the same plane on the body of the pipe. now the water under pressure comes in the chamber mid way up the pipe and fills the chamber with water and the air is compressed to the power of the
pump. The other fitting is connected to the service
line for the water system ahead of the "T" for the hot and cold seperation.
This is a way to increase the amount to water that can be used, before the pump in needed to re-pressurize the system and gives a much greater flow volume.
Now as far as the check valve on the pump, you may need to disconect the
line in and out and look for some contamination in the check valve spring and ball orafice. I have done this on our 86 HUNTER 31.4, it work well. and you may have a small leek at some connection or Ihave also seen a small
line puncture with a screw that was install to hold something else that caused a small leek. I hope this may help.
S/V "Faithful Girl" 32' 1986