Those are exactly the valves I was referring to. My boat has two of them, one for each of the separate AC cooling pumps. The check valves are there so that the genset and engine can't suck air back through the AC pump.
If the only possibility was to back flow water, you might be able to skip it, but if you follow the AC cooling water line far enough it exits the boat at, or just above, the water line. If you flow backwards though it, you will pretty soon pull air into the seawater manifold. This is most likely if the seachest strainer is a "little bit" clogged, but can not be ruled out at any time. Centrifugal pumps offer no resistance to back flow of either air or water if they are not running. The need for a check valve is independent of the specifics of the Calpeda pump, it is needed for any centrifugal pump.
A check valve is not needed on the engine and genset raw water cooling circuits because those are positive displacement pumps and significant back flow is not possible (assuming all the vanes are on the impeller!)
A failed open check valve on the AC pumps would be something to look for in case of a mysterious or occasional overheating or if there is frequent impeller failure on the genset or main engine that can't be traced to other causes.
On any plumbing system that uses a single source (the seachest) teed to multiple users some means of backflow prevention is required. Either positive displacement pumps or check valves are needed on each circuit, or you will pull air back into the suction of the running pumps.
Key West, FL
---In amelyachtowners@..., <yahoogroups@...> wrote :
Duane, & B Kinney,
The check-valve Duane is referring to is on the output line of the Amel installed Calpeda AC Impeller Pump. This valve keeps unpressurized water from flowing back into the pump and sea chest when the pump is OFF. I am not sure why it is installed, but I have several theories.
Each of those March pumps I have seen installed on an Amel is a victim of rust. That particular pump is not really marinized for saltwater installations. If you use that pump, keep a watchful eye for rust. As you probably know, the toilet flush water-siphon break system is above the A/C pump on a SM. You may be very careful to keep saltwater off of that pump, but will get drops from the siphon-break.