In a past life I went through a lot of dry pumps on the twin Cessna.  We did a lot of testing and found some easy ways to extend life.   To test, we turned a pump with a motor in the shop to see the temperatures.  The pump without airflow will get VERY hot and needs external airflow.  Once we ducted airflow with those addon plastic housings, life was extended on the airframe.  Also, we disassembled worn pumps and found the carbon blades worn at the edges and getting thin.  Turning the pump backwards broke some of those blades.  This means that if you have someone turning your prop backwards on a worn pump, it might lead to premature failure.  I tried to prevent anyone from moving the prop backwards and you can't imagine how often that happens.  Hope that helps.

I'm certain the cooling and lubrication from a wet system is part of the reason they last so much longer.  Cooling is probably the prime requirement in a dry pump.

Paul

Spruce Creek

On 2012-01-23, at 7:50 AM, Charles Brown wrote:

My experience with two wet vac pumps on a C-310 is that they never failed.  But they're rather large and heavy?  as I recall.

On Jan 20, 2012, at 1:36 PM, thomas williams wrote:

a wet vacuum pump is VERY reliable compared to the dry pumps.

=