A trip to bunnings resulted in this contraption.
My blueseas water maker does not like getting air in the system and even though the salt water intake is low in the hull, any air that is draw into the system accumulates in places like the pre-filters and eventually stops the main pressure pump from working. Easily fixed with a quick back flush of fresh water, but I thought "Wouldn't it be great if it never happened"
Water comes in the centre connection of my new fan-dangled device and out the bottom to the pre-filters. Any air goes out the top and there is a ping pong ball trapped inside the top section that acts as a valve. There is a small priming pump (came with the w/maker install kit) that feeds the centre section. Works like a treat.
Well it worked like a treat after I put small holes in the ping pong ball so that it would fill with water and become heavier. The problem was that it sealed so well, that the air pressure was able to hold the ping pong ball at the top of the contraption and not let the air bleed out.
Took it for a test on the weekend and I could actually see the odd bit of air being released form the system as the discharge is into the galley sink.
If you want to make one, it is from pressure pipe and just take a ping pong ball with you and find the pipe that it just fits inside. There is not much clearance. I had to glue a bit of pipe inside the "T" joint to the ping pong ball could not drop to the lower section. (this would not be good) The bigger the lower section of the contraption is the better, as it gives you a bit more surge capacity if it gets a gut full of air.
The ping pong ball valve idea came for those snorkels we had as kids. (well some may be old enough to remember them)