Broken strainer cap of water pump

[Elcano]

Hi,

I have another quite strange phenomenon on our SO409 and hope to collect some ideas how to solve it.

Here is the culprit (pump: Johnson WPS 3.4 12V):



The lid cracks within a couple of weeks in use. It is already the third one this season! Given that the lid is quite sturdy plastic there must be some pressure going on in this system. In the beginning I thought I tightened the lid to much so it cracked. I can definitely rule that after three tries now.

I guess I have some congestion in the system that causes the high pressure, or? Do you guess the problem is between water tank and pump or between pump and outlets?

I installed a nano filter from Alb (https://alb-filter.com/pages/nano) but had no troubles with it in the last season. To rule it out as a problem source I took the filter out before I installed the last new lid.

In the beginning of this season I discovered that I left a piece of kitchen towel in the water tank when cleaning it last winter . This caused a congestion of the valve which sits between the tank outlets and the water pump. Cleaned it about 30 times during the season   so I hope that there is no paper towel in the system any more, at least I did not find some for the last months.

So, do you have an idea what causes the pressure in the system and how I can normalise it?

Thanks as always.
Cheers

[zaphod]

That is a strange problem! I had my suction strainer crack once, but we discovered that in early spring after a particularly cold winter, so I assumed it had water in it and froze.

It is difficult to imagine any scenario where enough pressure can build up on the suction side of the pump to crack the relatively thick plastic cover. Any pressure increase on the suction side would just equalize to the water tank. If there was a blockage between the tank and the suction strainer you wouldn't get any water out of the tank. I suppose it is possible that pressure could build up in the water tank if the vent was plugged, and the tank was filled to the very top with no air space for thermal expansion, but it seems a highly unlikely scenario.

I would think about other factors besides pressure. Are you over-tightening the cap? It is an o-ring seal, so doesn't need to be very tight. You said you swapped out the strainer for a different type; is that strainer slightly larger than the original, and causing stress on the cap when you tighten it down? Are the caps you are replacing the correct part for that particular suction strainer? Maybe replace the entire suction strainer rather than just the cap to eliminate that possibility.

[Elcano]

Great points zaphod,

especially love the idea if the "over filled" water tank, because that is what i did recently and very close to the last refill the cap broke again.
I do not think that it is over tightening, because last time I changed the whole strainer and I installed it the way it came out of the box.

So I will buy another one and do not over fill the tank.

Thanks a lot

[Don Reaves]

I cannot imagine enough water pressure on the suction side of the system that could crack the cover. There must be something wrong in the design of the filter. Perhaps the screen is a bit too tall, and is applying pressure to the cover when it is screwed on. Or the body of the filter is warped and the cover is being bent when it is in place. Does the crack always develop in the same direction?

Personally, after the number of failures you have experienced, I would be looking to replace the entire assembly from a different manufacturer.

[allegria]

Hi Elcano,

This used to be a common issue on these water strainers.
See this old thread: jeanneau.proboards.com/thread/3250/cracked-fresh-water-filter-cover

Not sure there is a definite solution for your issue, short of stocking spare covers...

FYI, mine is 13 years old and never cracked, but I was talking with a Johnson rep at a boat show a few years ago and mentioned that issue and gave me a spare... I guess he knew this was a very common issue!

Cheers,
Allegria

[Elcano]

Nov 20, 2023 0:37:08 GMT allegria said:

Hi Elcano,

This used to be a common issue on these water strainers.
See this old thread: jeanneau.proboards.com/thread/3250/cracked-fresh-water-filter-cover

Not sure there is a definite solution for your issue, short of stocking spare covers...

FYI, mine is 13 years old and never cracked, but I was talking with a Johnson rep at a boat show a few years ago and mentioned that issue and gave me a spare... I guess he knew this was a very common issue!

Cheers,
Allegria

G´day Allegria,

that is golden, thank you!! I obviously searched for the wrong words . I also saw that the last one I bought was production date 2014. So got a new one in and ordered another spare lid. 
I also checked the brass valve and put some olive oil through it, now the valve works smoother.


I am trying to buy an elbow pump connector, so I can eliminate the strainer. Super hard to buy such an elbow in Europe. Does anybody have an idea? 60$ shipping cost over ebay is a bit much.

Thank you
Cheers

[Don Reaves]

Allegria -- Thanks for the reference to the older thread. I had forgotten the problem of the check valve reported there. My boat is 19 years old and I'm still using the original covers, but I don't think I have a check valve. Maybe that's the secret of my success.

[azmike]

Hello Elcano,  I had the exact issue with my filter cap also cracking. The problem was fixed by not over tightening the clear cap.
Just tighten enough so it does not leak.  
Hope this helps,
AZMike

[Mistroma]

Someone mentioned over filling the water tank. I can't see any possible reason for an over filled tank to cause the problem. The extra head of water would result in a miniscule increase in pressure. Even deliberately pressurising the system by blocking the vent and jamming a hose in the filler isn't likely to result in the cap breaking.

I'd agree it's over-tightening. I had one break after about 10 years and removed it every 6-8 weeks for cleaning prior to it cracking. I noticed that the o-ring had expanded over time and become a loose fit. I eventually had to push it into the groove and have 2-3 attempts to tighten before it would locate properly. I suspect it slid out of the groove when tightening and generated outward pressure on the lid when it cracked.

The new unit was much easier to replace when cleaning as the o-ring was a tight fit. Very little tightening needed to seal. I suspect I'd slowly become used to assembly issues and tightening a little more each time.