Question for the group, situation, the water pump when primed, it's intake is below the water line, runs for about 90 minutes then fails to function or seems to, attention is hard to maintain over this period and overheat safety drops the AC.  Reset the unit and it does not pump cooling water, if re-primed with hose it will restart.  I have a spare pump but have not replaced since it seems the original (12 years old) seems to function with prime.  There is no restriction to inlet apparent since when the priming valve is opened water flows to the bilge.  When restarting after failure the water pump motor is running but evidently not causing flow.  I would not hesitate exchanging the pump were it not for the functionality of the system when primed.

The system is a through hull valve to a strainer to a 3 way connection with a gate valve on the intermediate connection the through connection goes to the pump, the gate valve allows connection to a priming hose from dock water.  Were the impeller of the pump worn I would expect failure to occur sooner, were there problems with flow I would expect the flow problems to occur within minutes not after an hour.

Let the speculation begin, all answers considered and might even get a response.

HELP,

Tim

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Well---guess the obvious is the pump most likely losing prime. Now this I suppose usually occurs on intake side, but I am wondering if the pump due to wear could be eventually in cavitation . Even a very small pin hole on intake could cause the issue---not so sure about the cavitation idea.It also could be that the pump itself is sucking a very small amount of air due to imperceptable seal failure. Good luck--I had a similiar issue with my aft ac and for some yet unknown reason it cleared when lowered the pump bout 4''-even though thought every thing was below waterline.--Al

Timmy,  a few weeks back I lost my prime, I have the tops of the line March pump with the magnetic drive. There is a ceramic shaft that some how penetrated the plastic housing of the impeller assembly. Good your getting the ac running to finally complete your v berth ceiling ...right...get busy 'ole man... and remember Advil is "not" your friend!!!

B

Byron is on point.

These pumps are magnetic and not direct shaft driven they do wear out due to age.

1) Check the intake scoop under the boat ( Easiest done by blowing thru hose) and the strainer inside the boat. Make sure there is no restriction putting undo strain on the pump.

Replace the pump if #1 is correct.

These pumps are NOT designed to pull. They are designed to push!

Hope this helps!

Question...why would these pumps need to be self-priming?  Is the weight of the boat in the water and an open seacock not enough to get water up there?  If anything, I would think there would be regulators involved to control the flow.

I do not believe most are self priming--that is why they generally need to be flooded to perform. While it is true most -if not all are magnetic drive coupled--they still have a pump head and an impeller--. The pump head, due to corrosion etc could have a sealing failure and the impellor I suppose due to a decade of pushing salty/dirty water could wear to a point of inefficiency. I have never seen nor heard of a pump head that could not wear out--that said I still would vote for loss of prime due to a ''sucker'' side issue.

Thanks all and keep those cards and letters coming in.  The pump is a Cal pump because that is what shipped not the better March pump.  Prime is not the proper term since the pump end of the unit is below the waterline but the result is the same.  I think Al is right, the pump would work better if it were lower but it's in the vee bilge with little room to be lowered.  The problem with "priming" has existed since install which may also highlight the need for a little more head pressure on the suction side. The strainer is actually higher both inlet and outlet than the inlet to the pump, because of the problem getting the pump to push I added a tee with a hose spigot prior to the pump so I could push additional flow to the pump to start it.  Early on I even had a swing check valve in the line at the through hull valve believing against logic that water might flow uphill and drain the pump.

Byron, the 105 temps of last week precluded fixing this problem or working on vee.  Were I to complete that project I might lose the veil of near credibility I have with Liz when I tell her I'm going to work on the boat..  

LOL , just busting you chops, Ive been on my roof for  3 weeks patching , preping and rolling out 190 gallons of white silicon

The strainer shoul be mounted below the pump. Also I would suspect the valve you installed may be letting air in. You can test the pump by clamping off one ac feed line and see if the other ac unit pumps water. I would double check the inlet and the valveing 

Hope this helps

Chris 

Thanks  Chris, this is a single self contained  unit.  Ideally  the strainer would be  lower than the pump but geometry prevails, disallowing that option.  There is a possibility  the downstream  side of the valve may be leaking or even the inlet to the pump.  These will be the first checks since all else requires lifting carpet and flooring.

Tim

Tried to edit and timed out the 15 min.

The purge valve is about  an inch or two above the pump base/motor end (inlet down motor up).  When the valve is opened the stream is approximately  2" above the quick connect fitting, this probably  indicates 4" head minimum.

The gremlins have moved from my boat to some other boat.  Could not duplicate the problem today but it was not close to 100 so it was only an experiment not a need. Whoknows? Thought about going for a cruise but the evil power has dropped the water in the pool such that there is less than a foot below the props in the harbor and entrance. Waiting for water from Iowa to arrive probably around 8/2

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