Originally Posted by Freedom45
a64Pilot and Peggy
This is the schematic for my set-up
I have one manual and one electric pump
to evacuate the heads.
The needle valve is to throttle the vacuum bleed off.
The fresh water shut-off valve is next to the y-valve, I close this valve when switch to sea water.
I have exactly the same setup with the only difference being that I have a vent line hose running from the top of the cistern tank to a skin fitting (and above-water overboard). This serves the purpose of venting the tank to avoid vacuum, or as an overflow in the unlikely event that the float-valve fails and tank doesn't stop filling. The tank is connected into the toilet-feed system by the usual 3/4" hose which is tee'd into a Y-valve which can be switched to sea-water supply if required. It is extremely unlikely that contamination could come back through the feed pump
, up the gravity feed hose from the toilet, into the tank and then into the pressurized connection from the float-valve to the pump. However, in the event that the boat
is left unattended for a long duration and the fresh-water pressure feed pump is turned off, then a ball valve between the feed-pump manifold and the cistern tank is closed as shown by Freedom's most excellent illustration.
I typically close the valve, turn off the feed-pump and then flush the toilet (to empty the tank) when leaving the boat
. That way, no end of boat motion could cause the float to lift
permitting ingress into the fresh-water system.
for the tank can be found in the Sch40 plumbing
section of GnomeDepot along with a standard $7 flush-master toilet valve kit. The valve will actually fit into a Sch40 4" PVC tube if care is taken with alignment and placement etc, on the end caps. A Sch40 PVC female inspection
adaptor and cap can be purchase
in the same section as the pipe.
If you want to get really fancy (with an electric
toilet), you can connect a timed 12V relay across the terminals of the feed-pump for the toilet. That way you can set a "normally closed" actuated valve (set in the pressure-feed line from the fresh water system) to open for a set period once the toilet has been flushed to permit
refilling of the tank, only to close off again afterwards. However, this adds another possible failure mechanism with no substantial benefit!