450: Lagoon 450 water pressure pump will not prime when switched over to other tanks

[Sparky55]

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?

[donradcliffe]

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.

[Bean Counter]

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.

[Shrew]

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.

[Bean Counter]

Normal Lagoon 450 valve is a three way, when you open one tank feed it closes the other.

[Sparky55]

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
Sparky55

[bobfromcanada]

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 ....

[riv33]

Originally Posted by Bean Counter

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