How can a simple impeller pump fail completely?

[ndutton]

It has happened before . . . .

This also speaks to the importance of keeping the face plate gasket thin.

[thatch]

One last tidbit

Before installing the pump cover, I always lubricate the inside of the pump with either liquid hand or laundry soap. It does two things, first, it tends to close small gaps which will increase it's tendency to pump and secondly, it will lubricate it until it is actually pumping liquid.
Tom

[zellerj]

I always had problems with those paper thin gaskets getting mess up while I put the face plate on. I have since found that two small binder clips will hold the gasket to the face plate until the screws are started, then the binder clips can be removed and the face plate tightened.

[ernst]

It has happened before . . . .

This also speaks to the importance of keeping the face plate gasket thin.

Wow! That's sure more than a few thou!

I have a fruitful day behind me. I think you nailed the problem, it was at the very beginning. And, embarrassingly, it is possible that I messed it up myself...

But, do let's start at the beginning. First, I sanded the inside of the pump cover to make it nice and shiny, can't hurt. Then I did exactly what NDUTTON said, make sure water flows freely from the strainer. Well, it did not. I had the bad idea of sucking on the hose -- and got a mouthful of antifreeze. I got slightly wiser and used a small utility pump to suck on the hose but still no water.

Then I looked at the installation and noticed something which may be crucial. A long time ago (15 years?) I installed a nifty contraption that makes winterizing the cooling system very convenient: I installed a T that feeds into the strainer, with one input the seacock and the other a hose that I can put into a bucket with antifreeze. I put a valve in this hose which is usually closed. To winterize, I open the valve and close the seacock and the raw water pump sucks the bucket empty. Winterizing done!

What I now noticed is that I put this contraption (valve and T) just above the strainer (because it fits there...). I realized the top of the strainer is exactly at the water level, and the inlet of the pump is just below that (less than an inch). Now I wonder whether that is carefully designed to be that way. The problem (if it is one) is with my patent winterizing apparatus I have now several feet of hose an inch or two higher than the water level.

I have never had a problem with that but could it be that for some reason, this hose always remained filled with water EXCEPT for this winter, when the hose fell dry for some reason and therefore the pump was not primed? I thought I had excluded that possibility because, as I wrote in an earlier message, I had attached a hose to the pump inlet with its other end in a bucket of water that I held above the pump, and it STILL did not work. What I had NOT done, however, was to fill this hose with water! Since the pump is not self-priming, I suppose this 'test' was not really valid.

In any case, what I did today was to bypass the whole winterizing shebang and attached the hose from the seacock directly to the strainer inlet. Indeed, now the pump inlet was just below the water level. And water did flow when I opened the seacock!

Well, the rest was easy. I installed a new impeller (Globe run-dry) and gasket and turned over the motor. Water came out of the pump outlet immediately. I connected the hose to it and the motor was cooled just as it was supposed to be.

So, was that a major blunder that I committed with my clever (??) winterizing system? Should I be thankful that the problem occurred when I was safely in a slip, and not in some critical situation?

Or is it OK to have that hose above the waterline?

BTW, since I had brought all the tools I thought I might need, including a caliper, I did measure the old and new impeller and the pump cavity. The results were a bit surprising (to me). The new impeller measured 21.95mm (I find mm easier to use for this purpose, others may disagree) and the old one essentially the same, the caliper showed 21.93mm. This is rubber after all so I guess this difference is meaningless. But I was surprised by the depth of the pump body which I measured as 22.25mm. So it is about 0.3mm larger than the impeller. or a bit more than 10 thou. I was expecting it to be smaller. But the pump is pumping like a champ so I won't complain

Do you think I solved the problem? And should I do something about my winterizing system?

Thanks!

[ernst]

Before installing the pump cover, I always lubricate the inside of the pump with either liquid hand or laundry soap. It does two things, first, it tends to close small gaps which will increase it's tendency to pump and secondly, it will lubricate it until it is actually pumping liquid.
Tom

Great idea! Next time...

[ndutton]

Actually, these pumps WILL self prime when they are in newer, less worn condition. Your measurements indicate cavity wear (completely normal and expected as the pump ages) which explains its inability to self prime anymore. Because of that, designing the raw water intake path to be entirely below the waterline would help matters in the current situation.

But so would a new MMI 502 raw water pump that doesn't have cavity wear and will prime itself readily. Your pump is telling you it's about time to retire.

[JOHN COOKSON]

I don't know long the impeller was turning inside the pump dry. A dry impeller turning inside a pump will generate a lot of heat which can lead to shortened impeller life.
I finally got to the place where I primed the pump every time after I had it apart. It cut down on the "drama".

ex TRUE GRIT

[ernst]

Actually, these pumps WILL self prime when they are in newer, less worn condition. Your measurements indicate cavity wear (completely normal and expected as the pump ages) which explains its inability to self prime anymore. Because of that, designing the raw water intake path to be entirely below the waterline would help matters in the current situation.

But so would a new MMI 502 raw water pump that doesn't have cavity wear and will prime itself readily. Your pump is telling you it's about time to retire.

Good to know! So it looks my installation was not as stupid as I feared.

I am a bit surprised though that the pump already has considerable wear. As I said, this pump is not that old, it came new with the freshwater cooling system from Indigo that I installed 10 years ago (maybe a bit more). I haven't checked the hour meter but I guess the pump has only a few hundred hours on the clock. I use the Globe Run-Dry impeller for this pump (but NOT for the coolant side), could that have to do with the wear?

I think I will re-design the winterizing system. Thanks for all your help!

[ernst]

I don't know long the impeller was turning inside the pump dry. A dry impeller turning inside a pump will generate a lot of heat which can lead to shortened impeller life.
I finally got to the place where I primed the pump every time after I had it apart. It cut down on the "drama".

ex TRUE GRIT

I hope I won't have to do that

The longest time this impeller ran dry was when this event occurred, so this cannot have caused it. It does not look damaged at all. FWIW it is a Globe Run-Dry impeller so maybe that helped.