AC Cooling Pump losing prime

[markc]

Our AC pump (Calpeda Bronze centrifugal pump) is losing its prime sometimes when we are out on the boat for the day. The pump is just at sea level I think, and it has a non-return valve in the pipe about 600mm from the strainer. Part of the pipework probably does go above sea level, but that is unavoidable (and has been like that for a number of years) I know that the pump is not self priming, but I am at a loss to work out how the water is being lost in the pipework, It is certainly not leaking into the bilge as all joints are dry. The strainer is not leaking either. Could the rocking of the boat at anchor exert some type of suction effect through the strainer and it's sucking in air around the lid, but not leaking water? Or a similar effect when running at speed? Scratching my head on this one! Appreciate any thoughts you might have, cheers

 

[TK Blue MAX]

I would think that the non return valve would be my first thought, usually a spring and ball or flap arrangement, disconnect the pipe at the pump and back fill with water will probably be the easiest way to rule the valve out.

 

[Portofino]

Could you move the pump nearer the strainer ?keeping it about sea level .
Air will be getting in allowing it to drain down now , that was not before .

So assuming this moving the pump very close ( elimination of excess pipage ) means it does not matter where the air is finding its way in , you don’t have to chase your tail and if it’s about the same H with less than 30-40 Cm pipe from the strainer it will pull / prime if it’s empty.

As an aside snorkel in and see if your AF team have not caked up the inlet grill ....take a knife !
Rationale here is it sucks what it can always working against the new semi blocked orifice , but when @rest the dia makes it hard for it to resume a day or so later .....long shot but it’s a possible difference from previous years .

Sometimes the lazy 8uggers ( a first day on the job min wage worker who never makes the end of the week ) just daubs over existing shells / growth .

 

[jrudge]

I would check non return valve

my generator waS doing this. Put in a non return valve. Better but not great.

replaced the ( looking fine ) impeller and all is well.

the pump wont Have a rubber impeller but it may have worn ? One way valve will be cheaper. You could also position the valve right after the sea Cock. New hose won’t hurt either. Mine was old

 

[markc]

I would check non return valve

my generator waS doing this. Put in a non return valve. Better but not great.

replaced the ( looking fine ) impeller and all is well.

the pump wont Have a rubber impeller but it may have worn ? One way valve will be cheaper. You could also position the valve right after the sea Cock. New hose won’t hurt either. Mine was old

Thanks J. I just found a new nrv in my parts bin so I'll bung that on right by the seacock. You're right that the impeller is bronze, but I'll see if it is replaceable... better than £800 for a new pump!

 

[MapisM]

I've got a Calpeda raw water pump also in my installation, but I believe it's only when the pipe goes upstream into the chiller (see pic below) that it goes above the w/line.
And as you can see, there isn't any non-return valve - which is in fact something I'd rather NOT have, in a raw water pipe.
And fwiw, it never needed to be primed - also after putting the boat back in the water from hardstanding.

Regardless, I would suggest you to kill two birds with one stone, so to speak.
I can't remember where exactly the chiller is placed in the F165, but I assume it shouldn't be too difficult to reach from there some point of the onboard fresh water circuit.
In which case, you could fit a T connector to it, with a valve, and fit a tube from that valve into the strainer.
You can't see the valve in the pic below, but if you look at the bottom of the strainer you can see a white hose connected to it. That's the one coming from the fresh water circuit.
This way, whenever you wish to flush the chiller with fresh water (which Condaria recommend to do at least once every year btw), you just turn the chiller on, open the fresh water valve and close the seacock, job done.

I said that you'd kill two birds with one stone because obviously by opening the valve connected to the fresh water circuit (which is pressurized), you would automatically prime also the Calpeda pump, whenever necessary.
Goes without saying that when you will use this trick just to prime the pump because you want to run AC, you must remember to close the fresh water valve and leave only the seacock open!

The only caveat is that you'd better not mention all this to Portofino, because it's part of the whole BodgeFlow system, which according to him is useless.
IIRC, he thinks it's better to leave all onboard metal bits soaked in salt water, but don't ask me why....

 

[MapisM]

You're right that the impeller is bronze, but I'll see if it is replaceable...

I think parts for that pump can be found, but I'd be extremely surprised if its impeller would be the culprit.
I'm assuming from what you are saying that other than needing to be primed occasionally, it runs fine.
And if that's true, I wouldn't even bother opening the pump to check the impeller conditions - let alone replace it!

 

[markc]

I've got a Calpeda raw water pump also in my installation, but I believe it's only when the pipe goes upstream into the chiller (see pic below) that it goes above the w/line.
And as you can see, there isn't any non-return valve - which is in fact something I'd rather NOT have, in a raw water pipe.
And fwiw, it never needed to be primed - also after putting the boat back in the water from hardstanding.

Regardless, I would suggest you to kill two birds with one stone, so to speak.
I can't remember where exactly the chiller is placed in the F165, but I assume it shouldn't be too difficult to reach from there some point of the onboard fresh water circuit.
In which case, you could fit a T connector to it, with a valve, and fit a tube from that valve into the strainer.
You can't see the valve in the pic below, but if you look at the bottom of the strainer you can see a white hose connected to it. That's the one coming from the fresh water circuit.
This way, whenever you wish to flush the chiller with fresh water (which Condaria recommend to do at least once every year btw), you just turn the chiller on, open the fresh water valve and close the seacock, job done.

I said that you'd kill two birds with one stone because obviously by opening the valve connected to the fresh water circuit (which is pressurized), you would automatically prime also the Calpeda pump, whenever necessary.
Goes without saying that when you will use this trick just to prime the pump because you want to run AC, you must remember to close the fresh water valve and leave only the seacock open!

The only caveat is that you'd better not mention all this to Portofino, because it's part of the whole BodgeFlow system, which according to him is useless.
IIRC, he thinks it's better to leave all onboard metal bits soaked in salt water, but don't ask me why....

Thanks P. To be honest, I can't tell it the pump is above the WL.. I suppose I should take some measurements and find out! It is quite a way from the seacock and strainer, maybe 3m pipe run. However, if I remove the venting nut from the top of the impeller housing when it needs priming, the sea water won't make it to that level on its own so I suspect that the pump or part of the pipe run goes above the WL.

The tip to use the fresh water could work well as the watermaker (with fresh water flush) is next to the AC strainer ?

 

[Portofino]

@MapisM ” IIRC, he thinks it's better to leave all onboard metal bits soaked in salt water, but don't ask me why.... ”
From your post ^^^ .
Only that metal stuff has already got suitable signed off by the manufacturer anodic protection ....er like your MAN engine .

CAT have well documented CAC failure due to there pencil anodes + dissimilar metals ...loosing a huge class action in the states .
So much so is the unreliability of basically there whole cooler set ups they life the CAC s as a chuck away part , every 6/7 years .

So picture the buyer .Two boats aged 8 .One MAN t,other CAT powered .

Due diligence etc inc survey ...bells n whistles....full monty check before flashing your cash .
With the CAT boat you need or your agent acting for you need to see invoices for NEW CAC s @ 6/7 years .
NOT a few quids worth’s of Gardena hose bits and “ I always FW flush them sir “
If not swallow a huge brave pill or walk away or ask fir a reduction circa from £7 K to £10 K per engine .

With the MAN engine failure of the permanently remote anodic cooling system never enters into the equation @ 6 y 16 y or 26 y .Nobody buys a MAN powered boats , or VP MTU etc and asks to see the new CAC bill in the history files every 6/7 years .

How ever you are right to protect other bits like your aircon gear with seawater running through .Again mine are connected to an external anode on the transom ....like the engines .

The saltier the water , the stronger the electrolyte concentration the better the anodic protection / Zinc will deplete.
A depleted zinc instead of a piece of machinery is what you want ,it needs encouragement


There you are ....those two hull anodes.....theres one on the S Steel bathing platform frame ....so Mapish ...are you saying I should dry stack the boat and hose down the frame every trip ....I think you are if you “ hose down “ flush your engines .

 

[markc]

Dammit, look what I started!