Tank Pump Out problem

[wislon]

Good Morning, I own a Jeanneau NC11 which is now just three years old. We have had consistent problems with the Jabasco pump which empties the blackwater (sewage) tank. It will work fine for several days even weeks and then, just when we need to empty the tank, it will grind to a halt, just as though it is blocked or, as if the battery is flat. Neither of these obvious faults are the problem and over the last two years we have thrown an awful lot of money at the problem. Electrical tests, pipe checking/cleaning etc etc, completely new pump - nothing resolves the problem and nobody including some very capable marine technicians where we are based, has a clue - including Jeanneau dealer and Jabasco. The guaranteed way to resolve it when it happens is to temporarily disconnect the main pipe from the blackwater tank into the bottom of the pump. The pump then immediately bursts into life, flat out and empties the tank as it should. This would point to a "vacuum" problem however, we have had another inspection hatch cut into the tank at an accessible point so that we can/could relieve any vacuum - no great rush of air and doesnt resolve the problem. Only by disconnecting the pipe as described above can we solve the issue temporarily. Could this be a "priming" problem?  Please if anybody has any ideas they will be very gratefully received. This issue has wrecked some of our holidays - I cannot remove the pipe myself - hands too large and a VERY restricted area, so we have in the past have to head back to home port to get it resolved. We have now, at more expense, had a diverter installed so we can bypass the tank, however that cannot be used in a Marina.

Help!!

Wislon

[rene460]

Hi Wislon, that sounds like a real pain in the behind.  

I am am trying to picture the system.  We sail on a lake system, so always use the pump out, but we seem to have a different system.  Black water enters our tank at the top, and our pump outs use an internal pipe from the deck fitting to near the bottom of the tank, which allows a vacuum pump on shore to empty the tank.  I am having trouble picturing which pipe you have to disconnect, it sounds like a very unpleasant job unless I have the picture wrong.  Is that pump a mascerator and centrifugal pump combined or some other type?

My first thought is a bit of a blockage which is freed when you remove that pipe.  Perhaps a very short radius bend in the pipe at the outlet of the tank.  A blocked vent also comes to mind but you seem to have excluded that possibility by opening an inspection hatch.

 I am wondering what sort of chemical treatment you use.  Some are little more than perfume, or biocide, but we use a locally available product which is supposed to have a biological action.  It certainly breaks down solids, and our local hire operator has had almost no blockage problems since he started using it.  We took his suggestion and it seems to work.  Look for chemicals which are environmentally friendly and which also use a biological action to break down the solids.  And always observe the old adage nothing in the toilet until after you have eaten it (and cherry stones, not even then)!

In the mean time, a simple temporary fix to avoid spoiling your days out is to purchase a porta-poti.  Quite cheap and very reliable.  Just check that your pump out points have a hopper to allow you to empty it.  It’s not really satisfactory to tip it down a shore based toilet.

Perhaps a picture would help us all understand your installation. This would make it easier to understand what is going on.

rene460

[ForGrinsToo]

Rene,

What is the product you find works so well?

Thanks,
Geoff

[rene460]

Hi Geoff,

Sorry I can’t recall the name at the moment.  I am about fours the wrong way from the boat for a funeral, but will try searching around and find it for you.  I think it is manufactured by a small Brisbane company so don’t know world wide availability.  I will endeavour to find out and come back when I have some information for you.

rene460

[zaphod]

What kind of pump is it? Jabsco makes both Diaphragm and macerator pumps. Diaphragm pumps are positive displacement, meaning that restriction on either inlet or outlet could cause the pump to lock up. An inherent design flaw in the discharge piping could be creating enough restriction to lock up or overload the pump.

A macerator pump is not positive displacement, so if there was a blockage preventing movement of the fluid the pump will still spin. It takes something physically jamming the impeller to make it stop.

Are you sure the problem is not electrical? Is the pump motor getting really hot before it stops? Many motors have overload protection built into them that will stop current flow if they are being overloaded. They will then restart once the motor cools down.

If it is a diaphragm pump you should consider switching to a macerator as it will deal with solids and wads of toilet paper better. A macerator also counts as stage 1 sewage treatment since it purees the sewage.

[wislon]

Thank you all for responding. We also have a deck fitting for a pump out facility but have never used it. The pipe we disconnect from the Jabsco pump which is a macerator as well, is the pipe from the holding tank which is under the floor in the bilges. It is 1" (25mm) internal diameter and rises almost vertically about 1.5 metres to the pump. The Jabsco electric toilet also has a macerator so everything in the tank is pretty much liquidised. This layout is common to all Jeanneau NC11's.

Yes we have tried an alternative power supply when the pump has ground to a halt. It has no effect. We have taken both the original and new pump apart to check the macerator blades for blockage and again never a problem. Always when put back in situ it works. Now we just disconnect the pipe from the tank for a moment and it works again. A total mystery!

We also use a holding tank cleaner called "One Chem". It is biologically friendly and does not contain any formaldehyde. It is manufactured here in the UK. One 25mill dose per 100 litre tank lasts for 14 days.

We don't need a Porta Potti as now have fitted a diverter. 

Any other suggestions for our problem will be gratefully received. 

Wislon

[rene460]

Hi Wislon, that description makes it a bit clearer.  If I understand you correctly, it is an intermittent problem, you pump out many times without problems, then one day you connect up and the stoppage occurs.  

The symptoms you describe sound rather like a blockage at the tank outlet leading to more vacuum than the pump can handle and the motor stalls out.  A bit surprising that it does not blow a fuse if there is one, or flatten the hose a bit, so I am not 100% certain.  It could be caused by something floating in the tank that occasionally is drawn into the outlet and blocks everything up.  When you disconnect the pipe, there is the pressure from 1.5 m height of fluid which is enough to push the obstruction back into the tank.

Considering the lack of other responses and the time and money already thrown at the problem, I would go one step further and install a tee fitting immediately under the pump.  This will give you a side tapping at that point, to which you can connect a simple vacuum gauge.  It can be something from an automotive supply store, which could easily be read every time you pump out, or even a simple plastic tube manometer, either probably best with a ball valve for isolation.  Make it full line size, so if all else fails, you can let a decent inrush of air by opening the valve, without having to disconnect that hose every time.  Each time you pump out, watch that pressure.  A very low pressure (high vacuum) certainly confirms a blockage scenario.  The hatch in the tank will not see the low pressure, as it occurs between the blockage and the pump.  The tank pressure will always be at atmospheric pressure unless the tank vent is blocked.  

It is very hard to think of something else that would fit your description.  Note that the normal pressure at the pump inlet will be a bit more than 1.5 m of vacuum, but at the point the pump stalls, if that is what is happening, it will be considerably more until you let some air in by releasing that hose.  Though a tiny leakage could quickly equalise the pressure without enough flow to dislodge anything, so you will need to be watching while you pump out.

If it is such a “floater”, getting it out is the next issue.  That extra hatch might help.  I would pump in lots of clean water and pump out to flush the tank until you have some chance somehow of seeing what is going on with a low level, inspection mirror and light, and devise some way of fishing it out.  Unfortunately if it is clear plastic it will be hard to see.  Not a fun job.  You could try using the suction pump out if one is available in your area to see if you can entrain it and remove it that way.  Just a possibility.

rene460

[wislon]

Hi Rene, Thank you for your response. I think your suggestion that the vacuum is in the pipe, rather than the whole tank makes sense. I had already thought about putting some sort of valve in the pipe just below the pump/moderator so that I could easily release any vacuum pressure, but haven't yet worked out how to do it. Your suggestion to also insert a pressure quage is a good idea but I haven't a clue what I need. I will discuss with my local engineers. I am conscious that whatever I do I don't want to reduce the bore of the pipe which may happen if I insert a tee section.

Thank you for your contribution - it gives me confidence that I am going in the right direction to find a solution.

Wislon

PS - forgot to say that it does sometimes blow the fuse which I suppose indicates the pump is under pressure?

[rene460]

Hi Wislon,

It sounds like progress is still slow.

A bit more description, I would not worry too much about the pressure gauge, it is what I would do to definitively prove the vacuum theory, but my wife would say I was making a research project of it, and with some justification.   The more important suggestion is to put that tee fitting in with a valve on the side branch, so you can open the valve instead of having to remove that pipe.  From what you have said, it will not be an easy job, but you would do it once, then the valve makes the pipe removal unnecessary.

I expect that some level of flush and drain cycles to clean out the tank will eventually reveal the cause.  If you can use a conventional vacuum pump out, the problem may disappear up the pipe.

A normal tee fitting with the straight through path connecting the existing pipe to the pump will be a minimal obstruction if it is the correct size for the existing pipe, but it is a reasonable issue to think about.  The side branch can be smaller if necessary, or equal size, just whatever will best fit the space.

The current the pump draws depends on the differential pressure across the pump.  When the inlet is blocked, that diaphragm pump can in principal draw enough vacuum to boil the water, though usually some physical limit will occur before the water boils.  In any case the maximum possible vacuum is one atmosphere, so about 14.7 psi or 101 kPa or about 10 meters of water column.

However, the amount by which the pump inlet pressure falls below atmospheric pressure just adds to the differential pressure across the pump.  And the current draw is about proportional to that differential pressure.  I don’t know the precise specifications for that pump, but my memory is that it is not a very high differential pressure.  Trying to draw vacuum will significantly increase that differential, compared with the normal discharge pipe pressure drop perhaps plus one metre or so of vertical lift.  Hence the current rises and will likely blow a properly sized fuse.

I hope that is a little help.  It is always helpful to be looking for the right problem, and I think you have properly eliminated tank vent blockage and so on.   Something in the tank has to be highly likely, a plastic bag or something similar.

rene460

[Hanzel]

Hi Wislon, reading your old post now for first time and can mention I have something same problem.
Our macerator empties normally without problem (due to environmental reasons at sea only 😝 of course), but sometimes it is running without pumping out.
I started to remove the one-way valve just before the through hull outlet, no succes unfortunately.
Than we found out that when we put some water from the outlet in direction of the pump, so on the outlet side of the macerator, the macerator starts to work proper. My idea in this is that at some moment after a specific time of no use, sometimes many weeks, the macerator is too dry to achieve the needed vacuum, once the flow from the tank side is in the macerator, it goes like hell.
As it is not easy to fill the outgoing tube to wetten the macerator, I found another solution, when pumping out doesn’t start, pump the waste tank so full that there is a pressure on, than remove the small hatch above the waste tank, put with your feet or hands some pressure extra on the topside and start the macerator. 100% effective, once it is going is continues!

Knowing above solution is effective but not normal……
Did you find another permanent solution?