I've often wondered but haven't been able rationalize an answer why the seawater pumps for our small diesel engines tend to be the flexible Neoprene or Nitrile flexible impeller type. Rather than pumps with centrifugal impellers such for our car's cooling systems. Or our bilge pumps for that matter.
Protocol is to partially disassemble our seawater pump every season and replace the nitrile or neoprene impeller. Or at a minimum at least inspect the impeller for tears and cracks. And if one gets distracted from the normal start-up protocol and fails to open the raw water seacock, by the time the engine overheat alarm sounds, the impeller is likely to have been "dry run" too long and will have disintegrated into pieces that can wreak further mayhem as they lodge in the heat exchanger.
So why aren't centrifugal type pumps assigned to this duty? Modern alloys and plastics I would think would be suitable for years of service? No need for annual inspection. And while it is never good protocol to let the engine overheat, if the seacock is left unopened, at least the pump and heat exchanger don't need servicing.
Protocol is to partially disassemble our seawater pump every season and replace the nitrile or neoprene impeller. Or at a minimum at least inspect the impeller for tears and cracks. And if one gets distracted from the normal start-up protocol and fails to open the raw water seacock, by the time the engine overheat alarm sounds, the impeller is likely to have been "dry run" too long and will have disintegrated into pieces that can wreak further mayhem as they lodge in the heat exchanger.
So why aren't centrifugal type pumps assigned to this duty? Modern alloys and plastics I would think would be suitable for years of service? No need for annual inspection. And while it is never good protocol to let the engine overheat, if the seacock is left unopened, at least the pump and heat exchanger don't need servicing.