Macerator filling with seawater

[Steve_in_lex]

I see there's a thread from 2012 on "why is my macerator filling with water?" but am starting a new slightly narrower thread.  My macerator stopped getting a prime toward the end of the summer.  Then yesterday, after running it for several minutes, it finally got primed and pumped things out.  It worked great afterward through several cycles, verified by looking through the viewing port at the top of the waste tank.

The problem is this: now (since the priming issue went away) the holding tank fills up with seawater pretty fast -- like, in 15 minutes or so -- when I don't run the macerator.  I checked on the head input end of the flow, and that's not
the problem.  Playing with the discharge seacock indicates that it's clearly coming from that end.  Any ideas on what could be causing this?  My suspicion is that something was blocking the macerator so it couldn't prime, which eventually got through there, but the foreign object is somehow causing the inflow of water.  Any ideas?  Could it be a siphoning thing?  Is there some kind of valve in the macerator to prevent back-flow, which might have broken or jammed?

Thanks....this is unsettling!

[KWKloeber]

 Steve,

Why is your sea cock open when not operating the macerator?

[Steve_in_lex]

Not sure there's any right answer to this, especially now.  But in the past, including the PO (and our boatyard), the seacock has been open without any problems.  I'll close it going forward, but am curious about what might have changed since the macerator stopped priming and then started again.

[KWKloeber]

 I've never ever had that problem of the backflow. Did have the problem of not priming.

I would look towards servicing the pump head, possibly the impeller is missing a fin or two 

kk

[mark_53]

But in the past, including the PO (and our boatyard), the seacock has been open without any problems.  I'll close it going forward, but am curious about what might have changed since the macerator stopped priming and then started again.

Maybe the line to the seacock has been obstructed since the PO and you finally unclogged it?

[Steve_in_lex]

I think a broken impeller in the macerator might fit the evidence best.  The boat's going to be hauled soon so I'll have them check it.

[Ken Juul]

The way my '90 is plumbed (tank-macerator-thru hull) back flow into the holding tank is normal.  The macerator seacock must be opened and closed each time.  I was told the acid in urine is very hard on the macerator pump.  The few times I have been far enough at sea to use it, I always let the holding tank partially fill with sea water then pump that overboard to clean the macerator.

[Stu Jackson]

Not sure there's any right answer to this, especially now.  But in the past, including the PO (and our boatyard), the seacock has been open without any problems.  I'll close it going forward, but am curious about what might have changed since the macerator stopped priming and then started again.

Steve,

There is a right answer to this.  There was some serious blockage if you were actually sailing around with the macerator thru hull in the open position and you weren't getting big time back up into your holding tank.

That explains it.  The manual says: "Close the macerator valve immediately after emptying the holding tank."

The manual, if you don't have a hard copy, is on this website.  I recommend that folks not only have their printed copy but also download a copy to their hard drive of their chosen computer device.

Then it helps if one reads it occasionally.  And especially when an issue like this arises.  And regardless of what some (dumb?) PO and a (dumber?) boatyard told you.

RTFM always helps.   

To end your curiosity, what happened was some major big clog got cleared for some reason none of us can possibly imagine or ever know for sure, and you started back-flowing because you didn't close the valve.  Mystery solved.