Water pump airlocked?

[samwise]

I cannot get any flow from the taps in our pressurised fresh water system. The pump runs, there are no leaks that I can see and the accumulator also looks ok.

The problem arose after the tank ran dry when a tap was left running ( at a comparatively low rate) for about three hours. It is a Flojet diaphragm pump, so I don't think it has burned out.

I refilled the main tank and opened all the taps in the system before running the pump. It makes all the right noises, but the taps remain dry.

I suspect an airlock. What's the best way to clear it and how can I establish that the pump is not damaged?

 

[Monique]

Happened to me.

Change the diaphragm and if it was me, I would get the pressure switch also. I seem to remember that they come as a unit. Mucho dinero too..

GL

 

[vyv_cox]

I suspect an airlock. What's the best way to clear it and how can I establish that the pump is not damaged?

It would be extremely difficult to get an airlock in a system with a positive displacement pump, which a diaphragm pump is. It will self prime up to about 32 feet above the water and will always drive water ahead of it to the taps.

If the pump is running very quickly there is no water in it, suggesting that the inlet is blocked. If it runs more slowly, around normal pumping speed, it is likely that the suction valves are being held open with something. There is also the possibility that something else in the pump is faulty.

 

[AIDY]

Ha Ha... sorry it's not funny as it did the same yesterday too.

it caused me a lot of swearing.... in the end ihad to take the pump apart and fill it manually to get it to go. still must have an airlock in the system somewhere.... it always seems to happen to me when the tanks are low and i'm on port tack healing over, go down to check the chart and all i can here is the pump wortking overtime.

 

[VicS]

You do not say exactly which Flojet pump you have but generally diaphragm pumps are self priming even if located a couple of feet or more above the water level in the tank (Vyv's 32 feet is a bit optimistic, that's the theoretical maximum that any pump can suck up water). They can also be safely run dry. That does not necessarily mean that they can be run, even pumping, for prolonged periods.

Since it runs and makes no abnormal noises assume that it has suffered no damage from a prolonged period of running.

Very likely cause of the trouble is that some dirt has entered the pump and is preventing one or more of the valves from sealing properly, although this should not happen if you have a filter on the inlet. The filter could be blocked of course!

The trouble shooting for these pumps generally reads along the lines:

Failure to Prime - Motor operates, but no pump discharge
• Restricted intake or discharge line
• Air leak in intake line
• Debris in pump
• Punctured pump diaphragm (pump leaks)
• Crack in pump housing​

Check the filter ( if you dont have one put fitting one on the "to do" list)
disconnect the inlet pipe to check for a flow. If the pump is above the water level in the tank lower the pipe and ensure water will flow.

Dismantle the pump and clean the valves ... refer to the on line technical data sheet for your model of pump.

Rebuild with new parts as appropriate. There may be a kit .... see The Flojetshop for parts etc.

 

[samwise]

I have disconnected the feed from the tank and there is water coming through. There is a filter and it may be that having run the supply so low, there is some crud in it. I am always optimistic that there is a simple fix for these things that does not involve dismantling -- I am usually disappointed! Many thanks guys.

 

[dingdongs]

just a thought but can you get at the pump and instead connect a hose pipe instead and extra pressure may force the air lock out by leaving furthest tap in system open.alternativly try to connect a bleed tap into the point of the highest pipework.may also be able to blow air locl the opposite way back towards pump if you leave pipe dissconnected at this end.you have a similar situation as a heating system in which you bleed rads of air to get it circulating around the home.cracking a joint may help to get rid of air too.good luck

 

[vyv_cox]

You do not say exactly which Flojet pump you have but generally diaphragm pumps are self priming even if located a couple of feet or more above the water level in the tank (Vyv's 32 feet is a bit optimistic, that's the theoretical maximum that any pump can suck up water).

I confess I have never actually tried it at 32 feet, but a 'couple of feet' is somewhat on the pessimistic side. Assuming no leaks on the suction side I think 10 feet is realistic.

 

[NormanS]

You can have a lot of fun using a dinghy pump on the air breather pipe for the tank. It creates a slight artificial head, and IF the problem is really an air lock, it might clear it. Requires pumping with the dinghy pump at the same time as running the electric pump.

 

[VicS]

I confess I have never actually tried it at 32 feet, but a 'couple of feet' is somewhat on the pessimistic side. Assuming no leaks on the suction side I think 10 feet is realistic.

It depends on the pump. Most of the Flojet ones are spec'd to self prime up to 2.4 m but not all. (one is only spec'd at 2.5ft /1.76m )
So even 10 feet is optimistic or unrealistic depending on the pump.

I did say a couple of feet or more

If we had been told the pump type I could have quoted the specified figure

Whatever, the pump should self prime ... hardly likely that it is mounted too high to do that. If everything is in good working order then games with dinghy pumps or manually priming should not be necessary. If it is then it is time for an overhaul.

 

[NormanS]

The suggestion re the dinghy pump was based on personal experience. My boat has a "grey" tank for the galley and shower well. On one occasion when the pump wouldn't lift, rather than attack the relatively inaccessible pump, I pressurised the tank with the dinghy pump, while blocking all the possible vents. This forced water through the diaphragm pump, which presumably dislodged the foreign body which was holding a flap valve open. The pump has worked perfectly ever since.
I wouldn't reject an easy possible solution, without first trying it.

 

[rogerthebodger]

I had a similar problem with the pressure system on my new boat and it took several months to find a small leak in the suction side.

The problem I had was that I could get the system to work by priming the pump but when I connected the tank feed pipe the pump started to pump air in the water and the pump would cycle as if a leak in the pressure side.