So why does my Generator impeller last forever.

[Dockhead]

Originally Posted by Garrettw

I have done several things over the years on my Onan MDKBH. At one point I was running an electric AC motor for the raw water and bypassed the belt driven pump. This wasn't 100% reliable though because the generator wouldn't always stabilize the AC output in enough time to get the pump running before the low flow alarm tripped.

For the last 5 years I have something that is kind of verboten in the boat world: a check valve. I have used a check valve to keep a slug of water in the raw water intake line. This has solved all my impeller issues and they last the full maintenance interval and beyond with all vanes intact, every time.

The bane of above-the-water line raw water pumps.

My main engine raw water pump is below the water line. The impeller lasts forever. Even starting and running the engine with the sea cock closed doesn't hurt the impeller because it's still bathed in water.

My generator raw water pump is above the water line and needs to prime. It does not last forever. And like the case of the OP, it self-destructs in about 20 seconds if I forget and start the genset without opening the sea cock.

A check valve might help but I think for constant speed generators an electric pump is the right solution. I would use DC for this.