Macerator Pump - Why do they only work once?

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Shawn R.T. Severn

The macerator pumps (fore and aft) on our P450 have both been replaced twice. Both pumps have failed again. They simply refuse to work more than once or twice. They have got to go!!!! What would be a good mechanical, reliable pump to replace the electrical pumps? The second problem is the sensors in the tanks. Since there is no way to get a visual look at the volume. The sensors last about as long as the pumps. They are the floating type. The semi-solid nature of the material pretty much fouls them in short order! Any suggestions?
 
Dec 2, 1999
15,184
Hunter Vision-36 Rio Vista, CA.
Plastic or Metal tanks?

Shawn: If you have plastic tanks you can just purchase the Acugage system that is here on the site. Good reviews and they are external to the tank. If you have metal tanks then they have a solution for that too. Check out the HOW Store. There has got to be some problem with the installation of your pumps if they are failing so quickly. I am wondering if the salt water is corroding something in the pump? You may want to contact your mfg to see what they say about these pumps.
 
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James Taylor

Check your macerator pump installation

If your pumps fail so readily it suggests an installation fault. Check that the outlet of the pump goes to an "open" seacock. Operating a pump against a closed seacock will surely damage some types of pumps. Also make sure that the hose size from the pump to the outlet seacock is compatible with the pump. One designed for an inch and a half outlet may suffer damage if only 3/4 inch hose or seacock is used.
 
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Shawn R.T. Severn

Pumps are installed correctly

The pumps are installed correctly. I had this checked after the first pumps stopped working. I think I would like to switch to a mannual pump. Any ideas? Thanks for information about the pump indecator. I have aluminum tanks, so I will need the internal installation. I am still not sure that is will improve the situation. The installation sounds complicated.
 
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Peggie Hall/HeadMistress

I'm betting that your macerators...

are above the top of the tank and several feet away from it. Macerators are impeller pumps...when impellers spin dry for more than a second or two, the friction heat fries 'em....even that second or two degrades 'em. If a macerator isn't used for a while, the seawater and waste dry in the impeller housing, "gluing' the impeller to the housing. If it's stuck tight enough, the force from the motor will break a vane and the impeller can't impel anything with a broken vane. So either move your macerators to a location that's level with or below the discharge fitting on the tank, and within a couple of feet of the tank...or replace 'em with diaphragm pumps (the SeaLand pump is my choice for an electric). Diaphragm pumps CAN run dry without harm.
 
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Peggie Hall/HeadMistress

A couple of afterthoughts...

Sooner or later--prob'ly sooner--you're gonna have to replace your aluminum holding tank...metal holding tanks (doesn't apply to water or fuel) typically start to leak at a seam or a fitting within 2-5 years. So I wouldn't bother with a gauge till you replace the tank...and then I'd go with the Snake River guage. And it occurred to me after reading James' response to wonder if you ever start the macerator before turning the y-valve in the pumpout line from pumpout to dump out. 99% of macerator failures are due to a "fried" impeller...and since you've had to replace your macerator twice, that's GOTTA be your problem. Find out why the macerator runs dry long enough to fry the impeller, make whatever modification is necessary to keep it from happening, and you'll solve the problem.
 
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Shawn R.T. Severn

They are above the tank

Both of the macerator pumps are above the tank. As you know the tanks in the P450 are well below the water line. I am sure the blades are running dry. I think I will end up replacing the pumps with the SeaLand versions. I am a little worried about the leaking tank. Removal and replacement would be a major construction project on this boat. Has anyone come up against a tank replacement yet?
 
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