SeaLand Macerator Pump - Inverted Duckbill Valves

[Capt.Don]

9 months ago I replaced a rotted out Jabsco macerator pump with a SeaLand T12 macerator discharge pump. It has worked well for us until this weekend. For those unfamiliar with this pump, it is a bellows type pump with 2 inline duckbill values on the macerator and sea discharge sides. Usually this controls the flow of pump - discharge holding tank through seawater thruhull valve.

This weekend I found the holding tank side duckbill valve was inverted (confirmed after taking apart the pump). I also properly reoriented the valve 3 times (at which point I gave up), and the both times I disassembled, the valve was inverted. I also found the pump flow was reversed and I ended up pumping seawater into the holding tank. This tells me BOTH duckbill valves were inverted, thus reversing the flow of the pump. I didn't think to check the seawater side valve (I will tomorrow).

I'm trying to figure out how the duckbill valves could become inverted. Other internet threads indicate that if you attempt to pump with the seawater thruhull closed, the pump will invert the seawater side valve. I don't believe we used the pump with a closed thruhull, but anything's possible.

In talking with SeaLand customer support, they were surprised that the holding tank valve would also be inverted. This would indicate a reverse flow under a lot of pressure.

A couple other considerations,

1) We were under sail, the boat was heeling over quite a lot, choppy seas, 6 knots boat speed - a lot of pounding. Could the boat's pumping motion cause enough pressure to invert the seawater side valve?
2) It is possible that the holding tank's air vent was under water. Could this effectively seal off the air intake, causing a vacuum in the holding tank and cause the duckbill valve to invert? Could this be the source of the water flow into the holding tank?
3) The contents of the holding tank were sloshing around - could this motion cause enough pressure to invert the duckbiill valve?

I'd like to understand what could cause this. Any ideas or thoughts are most appreciated!!

Thanks
Don

[donradcliffe]

Assuming the valves were open, it could be a blockage between the pump and the tank. My guess is that the tank would rupture before the pressure built up enough to invert the joker valve.

[Capt.Don]

Before this became a nasty situation, I also thought it was a block in the holding tank. In sorting through this, I did not find any physical block (e.g., TP or such). There might have been an airlock situation, as the contents were sloshing around in the tank.

Another thought - a couple weeks ago we used a shore based pump-out. Another claim on the internet is if the macerator thuhull is open while pumping out might cause the valves to invert. The SeaLand rep didn't believe this was a possibility. I can't be certain this did/didn't occur.

I'll diagnose this further tomorrow, looking at the tank's air vent and both sets of valves. Very strange behavior....

[Seawindii]

Don, I am considering adding a sealand pump to my system so I am interested in learning what you come up with in the investigation.

When I read the Sealand manual online they recommend a vent loop on the discharge side of the pump for certain installations. Did you install it this way?

/att.
3. Vessels with an underwater discharge seacock or thru-hull must have a vented or anti- siphon loop installed well above the water line between the pump outlet and the seacock or thru-hull fitting. The vented loop should be plumbed with hose to a thru-hull fitting well above the water line.

[Capt.Don]

Yeah, I read that too. I know there's an antisiphon loop from the head to the head discharge thruhull, but there's not one on the macerator thruhull. The SeaLand installation diagrams do not show this antisiphon loop. I understand this on the head circuit; I need to think about why I'd need this on the macerator circuit. After this weekend's experience, I now understand their recommendations for (a) pump installed above the holding tank, (b) shutoff valve, (c) dip in the hose.... In all cases, I don't have room between the holding tank and the pump mount, so I'm taking my changes with future repair and maintenance.

Regarding the pump, I was tired of dealing with the Jabsco macerator pumps and their rotting out on a regular basis. This pump doesn't macerate, 100% plastic, so no parts to rot out. It was recommended by friends. It is around $100 more than the Jabsco, and I was hoping it would work flawlessly. I've used it regularly for the last 9 months without issue. Takes about 3 minutes to pump out our 17 gallon holding tank. There are some pump comparison videos that show this pump having trouble passing a blockage. I didn't think this would be a problem for us and I don't think a blockage caused last weekend's problems.

Off to the boat tomorrow to confirm all the fittings, duckbill valves, any blockages,....and do more tests. Hopefully I'll figure out what happened. Again, I appreciate everyone's ideas and comments.
Don

[HopCar]

"Another thought - a couple weeks ago we used a shore based pump-out. Another claim on the internet is if the macerator thuhull is open while pumping out might cause the valves to invert. "

When I read your first post my first thought was that your holding tank vent was blocked or partially blocked and a shore pump out had made a vacuum in the holding tank.

[Capt.Don]

HopCar - thanks - I'll be sure to check that out.....
Don

[donradcliffe]

When you replaced the Jabsco macerator, did you open up the downsteam plumbing to 1.5", or did you leave a 1" section in?? I can tell you from personal experience that having the output of the pump neck down to 1" is a REALLY BAD IDEA!!!!

[Capt.Don]

Don,
As per the installation instructions, I installed 5' 1 1/2 hose, with the supplied 1 1/2" to 1" coupling, with about 2' of 1" hose to the thruhull (item #7).
Don

[Capt.Don]

I received an answer from SeaLand that clarifies(?) this issue - their claim is my attempting to discharge while underway generated more than 17 psi on the system which inverted both duckbill valves. Recommendation is to NOT discharge while underway or to relocate the thruhull on the side or aft,or add a shield/cover. My thruhull is on the side, but no cover.

I'm still scratching my head on this - while underway, 6 knots, choppy seas. The speed alone through water only generates about 3 psi. I'd have to be moving at 30 knots to generate this type of pressure. I'm having a hard time believing that the pounding plus weight of water (@3' below surface) might generate 20 psi through 1" thruhull, which would then invert the sea-side valve.

Do you really believe that a sailboat, pounding into 4' seas, heeled could generate more than 20 psi on the 1" thruhull?

[Seawindii]

Earlier in the thread you said this happened 3 times. Was this on 3 separate occasions or on the same passage, for instance?

It would seem to me that if it happened on 3 different occasions you should be able to draw some common cause factors and eliminate those such as valves in wrong position while operating pump or during deck pump out, which would most likely be one time occurrences.

Does your SeaLand manual mention anything about pumping while underway?

Your experience seems to be a bit of an outlier based on my online research so here's hoping you find the cause and it's an easy fix. The pump has a great rep.

[Capt.Don]

I don't believe that cruising at 6 knots could generate 17+ psi to invert the valve(s). I do believe that the pump generates enough pressure to invert the valves, should there be blockage somewhere.

Since I plan on replacing the duckbill valves, I am going to experiment with discharge thruhull closed inverts discharge side valve, which in turn would invert the holding tank side valve. Before I do that, now that the holding tank is empty, I need to add a shutoff valve.

On the positive side, this feedback confirms that I'll keep the pump - I just need to configure so I can handle these odd situations, should they occur in the future.
Don

[Seawindii]

You are a warrior, my friend! Can there be anything more unpleasant than this?? I can only offer hope that your solution is around the corner. Good luck.

[donradcliffe]

Originally Posted by Capt.Don

I don't believe that cruising at 6 knots could generate 17+ psi to invert the valve(s). I do believe that the pump generates enough pressure to invert the valves, should there be blockage somewhere.

Since I plan on replacing the duckbill valves, I am going to experiment with discharge thruhull closed inverts discharge side valve, which in turn would invert the holding tank side valve. Before I do that, now that the holding tank is empty, I need to add a shutoff valve.

On the positive side, this feedback confirms that I'll keep the pump - I just need to configure so I can handle these odd situations, should they occur in the future.
Don

Cruising at 6-7 knots had nothing to do with your problems, but you are going to continue to have them. You have two options--put a macerator back in, or make the discharge plumbing all 1.5".

A couple of things you can do to minimize the problems--never put toilet paper in the toilet, and flush the toilet continually while discharging.

[Capt.Don]

I did some further testing - yes, if the macerator thruhull is closed and you run SeaLand T12 pump, both duckbill valves will invert. This could be caused by operator error, leave the thruhull closed -or- any blockage on the discharge side. In my case, as per SeaLand's recommended configuration, I have 1 1/2" discharge hose reduced down to 1" thruhull. In last weekend's situation, I don't know what caused this, but I suspect there was a blockage.

If it is true that there needs to be 17 psi pressure to invert these duckbill valves, there is no way that a cruising sailboat, at 6 knots, with the discharge thruhull on the side could generate enough pressure to invert these valves. The most I can calculate is around 4 psi (and that's generous).

Before doing anything else, I need to install a shutoff valve between the holding tank and the discharge pump and pumpout. That way I can either replace this pump or repair without emptying the contents of the holding tank into the bilge.

As a side note, I went with this pump after our standard issue Jabsco macerator pump failed and was noted that the internal screws holding the pump together rot out after a year. I was hoping this pump would be a better option; it appears that it has its own set of problems, e.g., replacing the duckbill valves each year, easily compromised,.... Any fantastic replacement suggestions??