Run a macerator backwards? - SailNet Community
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post #1 of 11 Old 07-26-2012 Thread Starter
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Run a macerator backwards?

I want to be able to rinse my holding tank out easily and efficiently. Filling it up three times and sucking the water out to rinse it clean isn't my idea of a good time.

I was thinking about wiring my macerator to a switch which would reverse the polarity and run the pump in reverse, pulling water in.

Has anyone done this before, or heard of anyone who has a setup like this?

I have Y valve installed that would keep the water from coming out of the deck pump out, so seawater going everywhere is not a problem.

-Nate

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post #2 of 11 Old 07-26-2012
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Re: Run a macerator backwards?

DON'T DO IT! Macerator pumps are not self priming, and with some models there are valves to contend with. Nice idea, but the best you can hope to accomplish by running it backwards is to burn out the pump and blow the valves.

The best method I've seen to scour the tank clean was on a Morgan 32.5. The owner installed a standard inspection port in the top of the tank, one that had a clear, removable port. It was a 6-inch diameter flush-mount deck plate with a clear center that screwed in place. West Marine has them for $14.95 (part #11743051).

After the tank had been pumped dry, he then removed the inspection plate, rinsed down the inside with a garden hose and spray nozzle, while at the same time the pump was turned on at the pump-out station. Within a few minutes the tank's interior was spotless, then the inspection plate was screwed in place.

Good Luck,

Gary
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post #3 of 11 Old 07-26-2012
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Re: Run a macerator backwards?

I'm not going to play engineer on TV, but that doesn't sound like a good idea to me. No access panel to just hose it down?


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post #4 of 11 Old 07-26-2012
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Re: Run a macerator backwards?

In brewing we used 360 degree sprayers that could be mounted with standard hose or npt fittings to clean large fermenters and kegs. It would be interesting to do as noted above with an access port that you could replace with the sprayer mounted on replacement cover. We used to do this to keg bungs (welded in) and such.

So, when you wanted to clean, you would empty the tank, then remove the access cover, replace with the cover with the sprayer and connect to a hose or we used to use hot water pumped from a tank with cleaner added.

Worked like a charm and removed VERY grungy gummy residues. Also, no need to touch anything. I think this would work great on at 10 gal holding tank as we were cleaning much larger vessels with them.

EDIT: Oh, and I agree on reversing the polarity on the pump, don't do that.

Last edited by AlaskaMC; 07-26-2012 at 09:50 PM.
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post #5 of 11 Old 07-26-2012
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Re: Run a macerator backwards?

I hear that if you run your macerator backwards, you stomach suddenly seems fuller...

David

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post #6 of 11 Old 07-26-2012
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Re: Run a macerator backwards?

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Originally Posted by djodenda View Post
I hear that if you run your macerator backwards, you stomach suddenly seems fuller...
LOL! That makes me want to cross my legs in fear

So, most definitely don't hook that baby up backwards!
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post #7 of 11 Old 07-27-2012
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Re: Run a macerator backwards?

Once the tank is pumped out, why not just fill it with water through the pump-out fitting (hose, buckets of sea-water, etc). Let it slosh around while you sail far enough to allow use of the macerator to empty the tank. From an eco viewpoint, there will be almost nothing in the tank to contaminate, but you won't be able to prove that if someone reports you for using the macerator close to shore. i know that there is no obstruction or valve on mine that would prevent filling the tank from the pump-out fitting, as that is how I clean it for winter storage in the boatyard (into a bucket under the macerator through-hull).

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post #8 of 11 Old 07-27-2012
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Re: Run a macerator backwards?

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Originally Posted by travlineasy View Post
DON'T DO IT! Macerator pumps are not self priming, and with some models there are valves to contend with.
His Jabsco "Leak-O-Matic" is self priming and even though it probably wouldn't hurt the motor to run in reverse I still wouldn't try it for several reasons.

The nut on the end of the shaft could back off, ruining the pumphousing.

The pump efficiency would be greatly reduced in reverse, if it pumped at all. You would probably fill the tank quicker by flushing the head.

If the pump did work in reverse would you really want to risk putting the blackwater tank under pressure?

On our RV we have a water flush attachment that connects to the discharge fitting and flushes the tank with fresh water during tank discharge. It would not be all that difficult to plumb a similar flushing device into the deck pump out of a marine sanitation system.

Or, of you have an extra fitting on your tank (or weld one on with a cheapo Harbor Freight plastic welder) you could attach an adapter to add water to the tank either from an auxiliary wash down pump or muni water.

Still seems like a complicated fix for a noncritical problem to me though.
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post #9 of 11 Old 07-28-2012
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Re: Run a macerator backwards?

Our RV has a built in holding tank flush that connects to a water hose. I see no reason that that would not work in a boat holding tank. The tank flush has a spinning head that washes the entire tank down inside. I run the pump when rinsing.
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post #10 of 11 Old 07-28-2012
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Re: Run a macerator backwards?

Quote:
Originally Posted by SJ34 View Post
His Jabsco "Leak-O-Matic" is self priming and even though it probably wouldn't hurt the motor to run in reverse I still wouldn't try it for several reasons.

The nut on the end of the shaft could back off, ruining the pumphousing.

The pump efficiency would be greatly reduced in reverse, if it pumped at all. You would probably fill the tank quicker by flushing the head.

If the pump did work in reverse would you really want to risk putting the blackwater tank under pressure?

On our RV we have a water flush attachment that connects to the discharge fitting and flushes the tank with fresh water during tank discharge. It would not be all that difficult to plumb a similar flushing device into the deck pump out of a marine sanitation system.

Or, of you have an extra fitting on your tank (or weld one on with a cheapo Harbor Freight plastic welder) you could attach an adapter to add water to the tank either from an auxiliary wash down pump or muni water.

Still seems like a complicated fix for a noncritical problem to me though.
Just to add to these excellent points. These macerators are designed with a directional flow head and means they are designed to flow best in just one direction. Sucking water in through the outlet and out through the inlet may not even work due to the head design. The motor control circuit would also need to be rewired as they won't spin backwards by reversing polarity.

Just fill & flush through the pump out... Each fall before haul out I fill our tank with a strong bleach & water mixture and let it sit for about a week on the mooring. We have a valve on the outlet so the bleach is not sitting in the macerator just in the plastic tank. I then pump it out and re-fill with fresh to do a final rinse. After a week of the bleach mixture sloshing in there the tank is spotless and smells like a hospital..

One trick with macerators is to keep them mounted just above the level of the tank fluid and have a valve between the tank and macerator inlet.. The acids in the tank can do a number on the macerator. Once ours is drained out the valve is closed and the macerator sits dry. When we need to drain the tank the valve is opened and the macerator pumps it out.

Our Jabsco macerator is about 18 years old, I have the receipt from the PO, and it is still going strong but it always sits dry without black water in it......

This is what the inside of our 33 year old holding tank looks like at the end of each season before winter storage... The dark spot near the top is the tank label on the outside of the tank. The hole at the bottom is the tank outlet that goes to the pump out and macerator.

I have never physically scrubbed it just blasted the insides with a hose and used the bleach/water trick each fall...

If you can valve it off and used the bleach/water trick I highly recommend it...


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Last edited by Maine Sail; 07-28-2012 at 08:44 AM.
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