Water tank plumbing

The twin fresh water tanks on our 43 Post have what I think is an unusual plumbing. As seen in the photo, the feed line comes from the bottom of each tank (not visible) and runs along at the height of the tank outlets until they get behind the centerline fuel tank. Then the lines rise up to about 1/2 of the water tank depth and connect to a 'T'. Below the 'T' is a check valve, then drops into the line to the water pump (located at the front of the engine room, about 15-18 feet away). That line runs at basically the level of the bottom of the water tanks.

With this setup the tanks gravity feed to the pump if they are over 1/2 full. Below about 1/2 full they become a suction feed, dependent on the check valve to hold suction/siphon until the tanks get to about empty. Once the water level drops below the top of the tank outlet fitting it will vent, drop the siphon, and you have to fill the tanks back up to over 1/2 tank to re-establish feed to the water pump.

Does anyone else have a setup like this? I can't think of a logical reason for plumbing this way, am I missing something? I am thinking to re-plumb so that the lines run at the level of the bottom of the tanks into a 'T', then directly to the water pump feed line. That should be a gravity feed to the pump anytime there is water in the tanks. Comments?

Pump is a Jabsco Par-Max HD diaphram pump. The rest of the line going to the pump is flat. There is a check valve after the pump to prevent back-filling the tanks when on shore water supply. If I re-plumb it I do plan to add a dump valve to drain both tanks for winter or flushing easier.

Thanks. I thought it was original, but I don't understand why it was done that way. It works ok (until the check valve wears out which I had to replace) other than de-winterizing you have to fill the tanks to above half before can start to pump out any antifreeze.

It might if let run (dry) a long time but the lines are 1-1/4" pipe going back to the 'T' and 1-1/2' hose to the tanks so it is a lot of air volume to draw a vacuum on.

Thanks. Would like to see your changes. Possibly one of the great Post mysteries, along with why they wired the 12 VDC system black+/white- like the AC system. Sure can confuse a mechanic unless they are told that is how it is done (and be somewhat dangerous).

Thanks for the suggestions. I prefer to leave the pump and accumulator in the engine room as they are better protected from water there than under the cockpit floor, it always gets some water around the hatch drain channels that makes it into there.

The check valve is made to be horizontal or vertical (I also have one in my basement utility sink which has it's own pump to get up to the main drain lines). What surprises me is it works upside down, which is how it gets installed on the boat. Going to look in more detail at re-running the lines after the boat comes home from it's winter storage.

It is possible the large lines running forward to the pump are to keep enough water volume to feed the pump as it cycles. I've not calculated the difference in flow resistance for the long run at smaller diameter.

My Viking had the belt driven pump with accumlator. I never considered the need for the accumulator since it was already there. It does allow the pump to cycle rather than run continuously at lower flows.

Thanks

I changed the tank plumbing. Here is the simplified version.

View attachment 100204

I 'think', based on a copy of a 43 Post manual water system illustration, the original arrangement used the backflow valve to keep shore water from filling the tanks as it did not show a check valve at the water pump. Our boat has been fitted with a bronze check valve just after the water pump and accumulator which keeps shore water from flowing back into the water tanks.

So far everything is up and running as desired.

Main body looks more bronze, machined surfaces on end fitting more brass. It was already installed and never questioned it. Does say it is lead free when looked it up.

Thanks for mentioning so I could check.