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Old 10-01-2018, 07:42   #1
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Lagoon 450 water pressure pump will not prime when switched over to other tanks

The port hull fresh water tanks are exhausted and have switched stopcock in port cupboard to starboard supply.
Jabsco water pressure pump will not prime?
Presume there is an airlock, any suggestions?
Are there any in line water filters standard?
(Have taken the cap off starboard tanks, there are full)
Any suggestions?
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Old 10-01-2018, 07:56   #2
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

I assume you left one of the water taps open full, to reduce pressure in the system. If so the next step would be to suck on the tap while the pump is on.
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Old 10-01-2018, 08:45   #3
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

Switch all taps off. Open faucet on cold in port rear bathroom. Turn on pump. Let it run for about 1 minute - you should get hissing and spitting of water and will then come good.. If still no good, could be clogged strainer or it could be an air leak in the system. We had similar problem and found the in line water strainer at the pump had a crack in the lid.
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Old 10-01-2018, 09:21   #4
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

IS there a shutoff on the feed from the tanks themselves? (There should be). With two tanks, if one empties, you need to close the shutoff from the empty tank to the pressure pump. Otherwise, the pump attempts to draw water from the feed line, however the vent in the empty tank and the empty tank itself is what is bleeding air into the feed side of the pressure pump.

Close the shutoff from the empty tank to the pump. The system will pressurize properly.
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Old 10-01-2018, 09:32   #5
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

Normal Lagoon 450 valve is a three way, when you open one tank feed it closes the other.
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Old 10-01-2018, 19:52   #6
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

Thank you for responses
I had an airlock in thehose between the hulls,
Pulled the starboard hose off and sucked!
Put some water in the port tanks,got the system primed and it seems to have cleared itself
Thank you for quick responses
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Old 11-01-2018, 10:41   #7
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

It's an airlock. Happens on my system frequently when I've rundown the one tank (and refill or switch to second or third tank). My fix was to install a tee fitting at the outlet of the Jabsco pump, a shutoff valve and about 2 ft of water hose (just enough to reach a bucket or the bilge). When it happens, run the pump and use the valve to tap off about a quart of water until you can hear the pump change tone indicating that the air has passed. Shut off the valve and you're ready to go. Got this trick from a helicopter pilot ....
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Old 12-01-2018, 05:26   #8
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

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Originally Posted by Bean Counter View Post
Switch all taps off. Open faucet on cold in port rear bathroom. Turn on pump. Let it run for about 1 minute - you should get hissing and spitting of water and will then come good.. If still no good, could be clogged strainer or it could be an air leak in the system. We had similar problem and found the in line water strainer at the pump had a crack in the lid.
I have to second Bean counters answer as 100 per cent right for the solution to the problem ( for us)

-we have had our L450 for just over three years and that procedure has worked every time
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Old 12-01-2025, 07:35   #9
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

Hi folks, first off after info on Lagoon 55, if I’m on wrong thread please let me know and direct to correct one if possible. I’ve followed this thread about fresh water supply problem, followed all the tips and still can’t get supply to stop surging. Both starboard and port water tanks are full and showing 100%. Have tried purging air as recommended, switching over both tanks at pressure pump location valves, pump is working. Does same purging from both tanks. Is it possible the bladder in the pressure tank under pump has lost its air pressure, if so any idea of what that pressure in the bladder should be? If I turn pump off at control panel then back on it seems to work fine for a minute or so. Sorry about the long winded question but it’s getting frustrating.
Regards Dan
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Old 12-01-2025, 09:43   #10
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

If bean counter's advice doesn't work, then suck the air out of the faucet in the bathroom. It won't take much if the pump works.
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Old 12-01-2025, 14:13   #11
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

The accumulator may have a split bladder. What model accumulator is it? The manual should contain all the detail you need to fix, replace and adjust air pressure.
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Old 13-01-2025, 03:50   #12
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

Greetings, and welcome aboard the CF, Dan.

Typically, the accumulator precharge is set to somerhing less than of the minimum system [pump cut-in] pressure.

See “Accumulator Tank pressure” https://www.cruisersforum.com/forums...re-263319.html
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Old 13-01-2025, 04:00   #13
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Re: Lagoon 450 water pressure pump will not prime when switched over to other tanks

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Originally Posted by Dan1961 View Post
Hi folks, first off after info on Lagoon 55, if I’m on wrong thread please let me know and direct to correct one if possible. I’ve followed this thread about fresh water supply problem, followed all the tips and still can’t get supply to stop surging. Both starboard and port water tanks are full and showing 100%. Have tried purging air as recommended, switching over both tanks at pressure pump location valves, pump is working. Does same purging from both tanks. Is it possible the bladder in the pressure tank under pump has lost its air pressure, if so any idea of what that pressure in the bladder should be? If I turn pump off at control panel then back on it seems to work fine for a minute or so. Sorry about the long winded question but it’s getting frustrating.
Regards Dan
Thank you all, turns out burnt out pressure switch relays on fresh water pump
Dan
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