Wednesday, October 1, 2008

GENERATOR IMPELLER

Upon starting the auxiliary engine we check for water in the exhaust 100% of the time.  Upon starting the generator engine we used to check for water in the exhaust 90% of the time, sometimes being lazy.  We should have checked today.  The generator ran twenty minutes this morning before shutting down.  The ALARM light was on at the control panel.  The TEMPERATURE ALARM light was on at the generator.

The inlet strainer for the generator was clean, but no water flowed from it when the lid was unscrewed.  The hose was removed from the seacock.  Water flowed into the boat.  The hose between the seacock and the strainer was the issue.  Unfortunately that hose is twelve feet long.  A big blow blew dark goo and mud from the hose.  Now water flowed easily and fully to the strainer.  The generator was restarted, but no water joined the exhaust.

The good news is the impeller is very easy to get to, and a spare was back on board.  A first spare had been loaned to sistership At Last, who recently had a similar impeller failure.  The replacement spare had just been received days ago.

The original impeller had completely disintegrated.  There were no vanes left on the hub.  There were a couple full vanes in the housing along with numerous pieces.  We hopefully collected enough rubber to be the whole impeller.  We will watch closely to determine whether the cooling system remains compromised with pieces that made it out of the pump toward or to the heat exchanger.  Right now there is substantial water flow in the exhaust, and the generator is running at normal operating temperature.

We learned a few things today.  Check for cooling water flow for every marine engine, every time the engine is started:  auxiliary, generator, dinghy outboard.  Don't bother hoping an impeller will survive running dry for twenty minutes.

The original impeller on the generator ran 240 hours.  Yanmar says inspect at 300 hours, replace at 600 hours.  With the long hose run from the seacock to the strainer, and then another fair length to the water pump, this impeller may need attention more often to keep its performance high and like new.  The instant failure might have been avoided if the contaminant that collected in the hose had made it to the strainer and not restricted flow.

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