I am not sure where we disagree.
You seem to accept that that backward flow through the AC circuit is possible. If it was not possible, why have the check valve? They only have one purpose: stopping reverse flow.
If water can flow backward, then it would not be long before the hose was empty and air was being sucked into the sea water circuit. Must be: because the discharge end of the hose is above the water line.
I can not address the toilet pump. My boat doesn't have one, I have never seen that setup, so I don't know what kind of pump it is or the piping details, or if there is a check valve.
Key West, FL
---In amelyachtowners@..., <yahoogroups@...> wrote :
I believe you are incorrect.
The engine and the generator have seperate connections to the Sea Chest which are "superior" to the saltwater manifold connection. In other words, the saltwater manifold is connected higher than the engine or generator....the only way that either the generator or the engine would suck air through the AC water pump is if the sea chest is clogged or turned OFF. If it is, either the engine or the generator would suck water/air through everything including the toilet saltwater siphon break. However, before any of this would happen the vacuum alarm switch (circa about year 2000) would be activated, energising the alarm and light.
Like I said, I do not know exactly why it is there, but I have several theories.