Sink water pump airlock woes

[kjohnr2001]

Morning all, drained my water tank via the bottom drain a couple of weeks ago and stupidly opened the tap to make sure it was fully drained. I appear to have got an airlock in the system - having read the threads on here, the advice seems to be to switch on the pump, open the tap, suck through the tap, close tap, repeat etc until the water flows.
I have tried this and even tried using a wet-vac without success. The pump is definitely running and if i put my finger over the end of the water spout I can feel air pressure building up but no water, no matter how long I leave the pump running for. My other problem is that I can't locate the pump - the van was converted when we bought it and I assume the pump will be either external or mounted behind the fridge, apparently installed by someone who never wanted it removed. I will try to get the van on a ramp over the weekend to have a look above the cover plate where the water filler and feed pipes disappear behind the body panels, but short of this, anyone got any other ideas?
Sorry this is a bit long winded but I would like to get this sorted before we go away agin, hate having to buy bottled water!
Thanks in advance,
K

 

[DXX]

It sounds like you don’t have a submersible pump but an inline pump. It isn’t positive displacement so won’t self prime.
I’m not sure how you fill water on your set up but in order to get the pump to pump water you have three options.

1. Backfill priming by putting water back through the tap to the tank via the pump, this may not work depending on the tap valve design and / or inline check valve if fitted.
2. Raising the water head to the same level as the pump or higher with an external header tank such as a portable tank raised high (on roof) with a sealed connection. The header tank would need to be vented.
3. Pressure filling the tank with a hose (don’t overpressure) with a sealed connection.

 

[The Bear78]

As above, @DXX beat me to it!
Pressurising the tank gently should force water to flow through any pipework and hopefully prime the pump. You may need the tap open to allow air to escape for this to work best. Failing that the sucking method could be improved if you can extend the tap with a length of tube.

 

[DXX]

The problem with applying a vacuum to the tap is if the converter has used cheap non reinforced hose (they will have) it will collapse and prevent flow.

 

[kjohnr2001]

Thanks both, should have said, the tap is filled via a hose through a simple filler point in the side of the van - will see if I can pressurise the tank somehow, but I have a feeling the pressure is likely to bleed through the tank overflow pipe! Will also try backfilling through the tap... Will let you know

 

[DXX]

Thanks both, should have said, the tap is filled via a hose through a simple filler point in the side of the van - will see if I can pressurise the tank somehow, but I have a feeling the pressure is likely to bleed through the tank overflow pipe! Will also try backfilling through the tap... Will let you know

You just need to have more water going in than escaping to raise the pressure, rags etc packed around will do it.
In case it happens again it’s worth having a modified tank cap with a hose connection.
Be careful that the tank vents are not inside the van or it‘s going to get wet.

 

[kjohnr2001]

You just need to have more water going in than escaping to raise the pressure, rags etc packed around will do it.
In case it happens again it’s worth having a modified tank cap with a hose connection.
Be careful that the tank vents are not inside the van or it‘s going to get wet.

Will do, have a try later today, thanks...

 

[kjohnr2001]

Update - just tried the tank pressurisation method, water flowing from the tap whilst the tank was under pressure with the pump running, took the hose out of the tank, no flow from tap. Tried pressurisation with the pump off, no flow. Tried the pump again, little spurt, then flow stopped, pump still running. Didn't want to try the backflow way yet as I am on my own at the mo and dont want to wash the interior - swmbo would be distinctly unimpressed....
Looks suspiciously like I need to find and bleed or replace the pump.

 

[kjohnr2001]

tiny air leak in the pre-filter cap - new o-ring and sorted...