Macerator "stalling out"

[smokey73]

I don't use the macerator much since I do not often get greater than 3 miles offshore.

When I last used it (earlier this year) it seemed to work fine and emptied the tank (legally)

Now, when I open the seacock and start the pump, it seems to run for a minuite or so and then just "stops". It doesn't seem to pump anything out. If I leave it off for awhile and try again it runs for a shorter time but again stops. I am thinking it sounds like a thermal cutoff to protect the motor to me. Any thoughts?

 

[Ralph Johnstone]

I am thinking it sounds like a thermal cutoff to protect the motor to me.

Does the motor feel hot to the touch ?

Does your boat have a battery monitor in your electrical system ? If so, check the amperage draw and compare to the macerator specifications. Something may be caught in the macerator impeller such as dental floss.

As a last resort, you may want to have a look at the internals of the pump section to see if there are any problems which leap out at you. At the least a repair kit, at the worst a new macerator.

 

[Sailor Sue]

Look for a big slotted screw on the ends of your macerator. If you find one stick a big screwdriver in and try to turn it back and forth a few times. Since your macerator gets used infrequently crap can dry out in the impeller so it sticks to the housing. When this happened in our boat it tripped a breaker and we lost all 12 volt for a bit.

 

[smokey73]

@Ralph Johnstone Don't know why I didn't put my hand on the motor when it stalled out I'm an engineer, ought to know that is something to check. I'll check the amperage draw next time I try to use it. Do you think it would damage the motor if I ran the macerator for a few seconds with the thruhull seacock closed. I don't envision being offshore in the very near future.

@Sailor Sue when I ran it I put my finger on the point where the screwdrover goes (like on a garbage disposal) and could feel the shaft turning and I could hear the pump running.

Maybe my discharge valve wasn't actually opening and I was trying to pump against shut off head? Would that cause it to stall out or trip the thermal overload. It doesn't trip the breaker, it just stops running. I can go for a dive in a few days and open the vavle inside and try to put something like a weedeater cutter up the overboard and see if it is actually opening? The seacock is relatively new (less than 5 years) and I cycle all the valves periodically, including the waste overboard (then I zip tie it closed to meet USCG requirements to disable the overboard discharge path.

 

[Rich Stidger]

Dan,
Definitely check the current draw. Mine draws about 20A when actually pumping and when the flow is done the current drops to about 10A and the sound changes dramatically. There is no harm running it dry for 5-10 seconds to check the current draw. It sounds like it isn't pumping and the thermal switch is opening. I have no idea how quickly the thermal switch trips with a dry impeller.
I put a short piece of clear vinyl tubing in the output of the macerator so that I can visually see when it is pumping. A flashlight shows the flow easily.
If your seacock is a bronze unit and not a plastic one, I would expect that a failed seacock is quite unlikely.

 

[JamesG161]

Do you think it would damage the motor if I ran the macerator for a few seconds with the thruhull seacock closed.

No!

No flow = minimum Amps pulled.

Jim...

 

[smokey73]

My seacock is bronze.

No flow, with the seacock open (ie tank is empty and pumping "air") would be minimum amps. However, if the seacock is actually not open or there is a clog in the line, then it would be trying to pump against shut off head and would be drawing more amps.

 

[JamesG161]

it would be trying to pump against shut off head and would be drawing more amps.

so you point is pumping air is less amps than water?

Ok true.

What is amp pull when pump is packed up with.... ?

Jim...

 

[JamesG161]

Cost now $190

Jim...

PS: I got one in 2021, $110

 

[smokey73]

First step is to check the currents and see if the pump is "hot" when it shuts down. Affter that, if not conclusive for any problem, guess next step is to remove the pump and inspect. Not a job I look forward to but

 

[smokey73]

Is the "run dry protection" that the pump shuts down? If so that brings up a whole host of other possible things to check. Maybe the pickup tube that goes to the bottom of the tank is not attached so it is drawing air. Maybe the tank is empty or below the level where the pickup tube does.

 

[Ralph Johnstone]

with the seacock open (ie tank is empty and pumping "air") would be minimum amps.

Yes, as P X V is at a minimum because :
- the discharge pressure P = 0
- the discharge volume V = 0

if the seacock is actually not open or there is a clog in the line, then it would be trying to pump against shut off head and would be drawing more amps.

No, as P X V is again at a minimum because :
- the discharge pressure P is now high
- but the discharge volume V = 0

The small amperage draw against a stoppage in the line is entirely due to friction in the pump body as it churns the water.

So amperage is not going to be much of a help unless there is a large friction in the pump due to bad bearings, the impellor is encased in , or something else causing higher friction rather than just water.

Do you think it would damage the motor if I ran the macerator for a few seconds with the thruhull seacock closed.

Nope, the only concern with the pump is that the mechanical seal is wet at all times.

I can go for a dive in a few days and open the vavle inside and try to put something like a weedeater cutter up the overboard and see if it is actually opening?

Excellent idea. Is it possible to use a coat hanger if you get a coat hanger and use it after measuring the length so that you don't jam it into the macerator pump ?

Do you think you could take the boat out past 3 miles (one anyway) and check the following :

1. Amperage draw with the discharge open and record.
2. Amperage draw with the discharge closed and record.

Can anyone think of any other exercises while he's out there ?

 

[JamesG161]

Can anyone think of any other exercises while he's out there ?

Yes !

Jog in place for 15 minutes.

Then buy a new one and fix the old one with the repair kit.

Jim...

 

[Ralph Johnstone]

Yes !
Jog in place for 15 minutes.

Yes, I guess a few deep knee bends wouldn't hurt either.

 

[Ralph Johnstone]

I put a short piece of clear vinyl tubing in the output of the macerator so that I can visually see when it is pumping.

Eeeew. That's disgusting .
I like it !

 

[smokey73]

Seems it would be okay since the discharge valve is shut when not in use. Kind of like the clear vinyl on the pumpout hoses I normally see. Still, though, one more connection for a possible failure point and a nasty one at that. @Rich Stidger what kind of hose did you use?

 

[jibes138]

What size wire is feeding the pump and how long is the run. These pumps pull a lot of amps and if the voltage drop is too large it can cause troubles. You could be right on the edge of it running or not and a little overheating kills it.

 

[Rich Stidger]

@Rich Stidger what kind of hose did you use?

It is just 1" ID vinyl hose from the hardware store with 1/8" walls. Not reinforced, nothing special. I have had it in place for almost 25 years with no issues at all. It has a smooth bore so nothing sticks or accumulates. One of these days I plan to put a small LED to backlight the hose when the pump is running so I don't need to get my flashlight.

 

[Rick D]

I don't use the macerator much since I do not often get greater than 3 miles offshore.

When I last used it (earlier this year) it seemed to work fine and emptied the tank (legally)

Now, when I open the seacock and start the pump, it seems to run for a minuite or so and then just "stops". It doesn't seem to pump anything out. If I leave it off for awhile and try again it runs for a shorter time but again stops. I am thinking it sounds like a thermal cutoff to protect the motor to me. Any thoughts?

Just FWIW, I had the same happen. Replaced the pump. Same thing. Checked for clogs on the input and outlet hoses. Clear. Finally, I found that the through hull was not opening. The handle turned with normal resistance but the ball was not turning and it was staying shut. Ergo, It was shutting off since it was running against a block. I had the through hull replaced the next haul out and all is well. I'm sure the fact that caustic mixtures get pumped through with a flush shortens the life of the through hull substantially.

 

[Rich Stidger]

Finally, I found that the through hull was not opening.

Was your failed thru-hull a bronze unit or a nylon-plastic type?