Caution! Jabsco 18590 macerator wired backwards!

[charris]

Cruising in Mexico, had a new Jabsco macerator as a spare, installed it after my original unit was slow to pump (found impeller needed replacement, missing blades). Installed in a marina, did not activate to pump out until offshore on a 10 hour passage. Flipped it on, watched the amps come up as the pump primed, stood watching the ammeter to flip it off when it started sucking air, when a terrible bang ensued and the floorboards jumped up a couple of inches. Poopy water everywhere. A nightmare. Volt meter confirmed +12V on red input, neg on black. Confirmed pump orange wire was wired to red +12V and black wire connected to black. Pump was running backwards, so instead of evacuating the holding tank we were sucking in seawater and pressurizing the holding tank to the point where it burst. Lovely.

Reversed the wires, so orange to black and black to red, pumped out what remained in the holding tank, fortunately it was the top of the poly holding tank that had blown, along the longest seam, with a palm sized piece flying all the way across the galley. Spent a lovely afternoon at anchor washing, bleaching, cleaning, pumping (the bilge pump became a poop pump for a while). Dremeled out the joint along the burst seam and used a couple of tubes of 3M 5200 fast cure in the groove. Should be enough to seal against sloshing. Long term - tank will need to be replaced $1000.

Purpose of the post is to try to help this from happening in the future. If you replace one of these macerators, better check and make sure it is rotating correctly, hopefully I was the lucky one and this is not a pattern. Hit the switch briefly and make sure the smaller hose (discharge) is discharging and not sucking. This was not a red letter day...

 

[Peggie Hall HeadMistress]

Are you sure that it WAS wired backwards...that you didn't set it down backward? 'Cuz that would certainly cause it to pull in sea water instead of pulling out tank contents. If that's the case, YOUR reversing the wires would have it running backward pulling waste out of what's left of the tank..
And speaking of the tank...it shouldn't have pressurized. All that sea water the macerator brought in SHOULD have just caused the tank contents to overflow out the vent...unless the vent was blocked. And $1000 seems like a LOT for any tank, especially one thin enough to explode that violently.

 

[charris]

Are you sure that it WAS wired backwards...that you didn't set it down backward? 'Cuz that would certainly cause it to pull in sea water instead of pulling out tank contents. If that's the case, YOUR reversing the wires would have it running backward pulling waste out of what's left of the tank..
And speaking of the tank...it shouldn't have pressurized. All that sea water the macerator brought in SHOULD have just caused the tank contents to overflow out the vent...unless the vent was blocked. And $1000 seems like a LOT for any tank, especially one thin enough to explode that violently.

Hi Peggy - thanks so much for your reply. The tank is a custom made poly replacement for the original Hunter aluminum tank. Was $800 5 years ago when we installed it. It is a thick, quality welded seam natural polyethylene tank, I guess the custom nature of it makes it that expensive. As to the pressure - I agree with you that the pressure should not have built up and it should have gone out the vent. I will have to check that, but hard to believe that the vent would plug to point where the amount of pressure that built would not clear the vent. As to the wiring - I don't understand "set it down backward". Can you expand on that? The install is an inverted position, in that the motor is below the pump, which is not desirable in the case of leaks I know, but all the plumbing is set up that way. But I don't see that this changes anything. Regardless of physical orientation, should not the pump rotation dictate which port is discharge and which is intake? Installed macerator orange to 12V and macerator black to ground, the 1" port sucked seawater and pumped out the 1 1/2" port into the tank. Would love to hear more from you about this if you feel something is not right. Thanks again Peggy for your input. Have seen your posts for years. What a wealth of information!!

 

[charris]

Hello again Peggy. Been thinking about the vent issue. As per most boat manfs - vents are never large enough. The vent on my holding tank is perhaps only 1/2" hose going to the typical 90 degree hullside fitting. After giving it some thought, my theory is that during the 2 or 3 minutes I was waiting for the tank to empty, it was filling at 10 gpm which I think is the rating on the macerator pump, and the vent could not release sufficiently to keep up with that volume. Pressure built, and then the tank finally blew. Cannot confirm that yet but seems logical. The holding tank pumps out rapidly, seems like this would not happen if the vent was plugged as the pump would be pulling a vacuum. Thank goodness it blew the top off only, this also seems logical as that is where the air is, and it let go on the longest seam which also seems to me logical that this would be the weakest point. With the tank 1/2 or more full, the liquid in the bottom half could not compress like the air above, so the bottom seams were protected. Pretty sure we are good to go in the morning, got a few hundred miles to cover to complete our passage so crossing our fingers that the sealant on the tank's top seam will hold against the sloshing. Will be keeping the holding tank as empty as possible. Our install permits head discharge only to the holding tank, so pretty critical that it "holds"

 

[Peggie Hall HeadMistress]

hard to believe that the vent would plug to point where the amount of pressure that built would not clear the vent.

Ohhhh, it can...as many a boat owner has found out when he was hit with a geyser upon opening the deck pumpout cap, or worse yet, had a tank imploded by a strong pumpout...or even managed burst a tank by continuing pump a toilet that had become increasingly hard to pump. Your tank must have already been so pressurized by continuing to use the toilet against a blocked vent that it only took a little more pressure from the macerator to finish the job. We prob'ly should have some one-on-one conversation about modifying your vent--diameter and thru-hull--before you order a new tank.

As to the wiring - I don't understand "set it down backward". Can you expand on that? The install is an inverted position, in that the motor is below the pump, which is not desirable in the case of leaks I know, but all the plumbing is set up that way.

By "set it down backwards" I meant oriented and plumbed it backward. Not likely if you installed it yourself, but who knows what "grunt" labor in a Mexican marina is capable of! Now that Jabsco is mfr'g everything in Mexico with materials from China and other offshore sources, it could very well have been wired backwards. You might want to upgrade to a SeaLand electric diaphragm pump:
SeaLand T-Series discharge pump A bit more expensive than an impeller macerator, but can run dry for quite a while without harm and lasts forever with no maintenance except replacing 2 duckbill valves every couple of years. I had one on one of my own boats that was 11 years old when I sold the boat and still working fine.

 

[charris]

Thanks for the further input Peggy. Checked the vent and it is clear. I didn't think it was going to be plugged as we have had multiple suction pump outs this winter in marinas and had no problems, and pumping the head - waste disappears rapidly, no hesitation due to back pressure. I checked the specs on the macerator = 12 gpm which is a pretty strong flow. I am now convinced that with the macerator running backwards and filling the tank at 12 gpm that all the air went out the vent and then the silly little 1/2" vent hose simply could not handle the flow, especially once you throw some partial solid waste into the equation. I'll take a look at the pump you mentioned - got a feeling that I won't be making this mistake again - but I think the Jabsco's are rather high maintenance by design. In 5 years I have gone through 2 of them, always attended in use and turned off immediately upon current fall off due to sucking air (tank fully pumped out). When I order the new tank I think I will spec a larger vent, can't go wrong with that and will help odor control as well I guess. Thanks again for all your input. Will have a look for your book - Amazon?

 

[Peggie Hall HeadMistress]

Will have a look for your book - Amazon?

Amazon if you want the Kindle edition...but if you want a hard copy, support this site by buying it from the sbo.com store! There's a link at the bottom of this page, and there may even be some signed copies left in stock.

(hit send too soon)...
Amazing that your vent isn't blocked....I'd have bet real money on it! I suspect that the issue is less the diameter of your vent line than it is the design of your vent thru-hull..."vent" thru-hulls are all designed for use on fuel tank vents, so they really restrict air flow. You want to go with a 1" vent and a straight open "bulkhead" thru-hull...the kind you can stick your finger in. That will allow you to stick hose nozzle up against it and backflush the vent line to keep it clear. You'll also want to put the vent fitting away from the hull, on a surface--preferably the top of the tank--closest to the boat's centerline, not next to the hull. By putting it inboard, you prevent tank contents from spilling out the vent when the boat is heeled.

 

[Ron20324]

Peggy probably did not mean to put the nozzle on/in the vent thruhull, as that is probably the same nozzle you use to fill the water tanks and such. I carry a 3-foot hose extension with no fitting on the end that I put nto the thruhull.

 

[Rick D]

Peggy probably did not mean to put the nozzle on/in the vent thruhull, as that is probably the same nozzle you use to fill the water tanks and such. I carry a 3-foot hose extension with no fitting on the end that I put nto the thruhull.

Good point. This is what I made to go over the vent cap.

 

[Peggie Hall HeadMistress]

Actually Ron, I did mean put the nozzle up against the thru-hull...'cuz I always removed the nozzle from my dock water hose when I filled my water tank so I could stick the end of the hose into the deckfill instead of standing there holding it. I thought everybody either does that or has a separate dedicated hose to fill the water tank.

The nozzle, unlike Rick's gizmo or the end of a hose, puts water into the thru-hull and down the vent line under enough pressure to wash out whatever is in it. However, anything that floats y'all's boats is fine as long as it works.

 

[Terry Cox]

Hey Rick, nice tool that you fabricated. Very similar to the one I made as a way to make sure the tank vent remains clear after each pump out. My last step is to run city water through the vent scupper using that tool while running the pump out system until clear water appears through the pump out hose.

I have followed this procedure since 2002 and the system has remained trouble free ever since. Plus, everything on our boat that is sanitation related is original including the Jabsco heads. Thank you Peggie Hall.