Black Tank Macerator Pump Flow Rate

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Paul M

Paul M

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Joined
Nov 17, 2016
Posts
29
Location
St. John's, Newfoundland, Canada
My front black tank is emptied using a factory installed macerator pump that discharges into the gravity sewer drain.  The tank capacity is only 21 gallons but it takes the pump about 15 minutes to empty the tank even when it is only filled with water.  My question is do others with this set-up experience the same thing or should I be looking for a blockage or other problem with the pump and/or discharge line.  The motorhome has only been in service for 1 year and the pump has always been very slow (not good if others are waiting for the dump station!).  Appreciate any comments or advice you can offer.

edit by staff - changed message icon to topic solved
 
My Winnie Era has a macerator, too, and it has always been slow pumping out the gray tank.  But, because it pumps the black water much faster (flow rate is higher), I'm convinced it is just slow drainage from the gray tank.  I haven't investigated further, but I suspect a shallow slope from the tank to the pump (there's not much room under there).  It seems the pump gets ahead of the gray drainage, but not the black.
 
Thanks for the comments. 

I think my Shurflo pump should be faster than it is (currently about 1 gpm).  It is rated at 13 gpm @ 0 head and 6 gpm @ 19 ft head (8 psi).  The pump is located below the black tank so it should have a positive suction pressure.  It discharges thru a relatively flat 1 inch discharge hose that is less than 15 ft long.  I will investigate further to see if there is an obstruction in the suction or discharge line or perhaps a worn pump impeller is the culprit.
 
Also, check the voltage as close to the pump as possible. Manufacturer's specs for the pump might be rated at 13.8 volts. Drop a volt or two and that's a significant loss of performance.
 
Don't feel bad, I have the same setup and yes it takes mine awhile to empty the Front Black tank.  It does have a tendency to work much better with more solids than water.
What you might want to do is raise the front of the MH some to help with the flow of the Black Tank.
You should also go ahead with checking the discharge side of the pump and the impellor also.  Those 2 things I still need to do. 
I have filled the Front Black Tank with nothing but water, and yes it takes awhile for it to empty.

I have thought about having the Front Black Tank discharge into the rear Black Tank then emptying it because I put a macerator on my system and like the NO mess setup much better.
 
For what its worth, my Flojet Macerator pump, pumps at 4-5 gallons a minute down a 100 foot 3/4" water hose.  This pump just connects to the 4" black/gray drain connector. 

It seems strange that a factory installed macerator pump is so slow. 
 
For what its worth, my Flojet Macerator pump, pumps at 4-5 gallons a minute down a 100 foot 3/4" water hose.  This pump just connects to the 4" black/gray drain connector. 

It seems strange that a factory installed macerator pump is so slow.

Thanks for the post.  I'd be happy with 4 or 5 gpm. I have an appointment to have it checked out under warranty this week.  Will provide an update after that.
 
For some reason the factory installed systems all seem slow compared to aftermarket. Gotta be plumbing, since I think the pumps are all at least 10 gpm. The discharge hose size & length is a major factor, though, as is the voltage that John mentioned. RV factory wiring is often undersized and the pump needs large amperage to function at 100%. The portable Sanicon that I had ran at about 20A with 13+ volts applied, so at least 12 gauge wire should be used.
 
Just curious... I understand the need for a macerator pump if you've got to pump your waste uphill, or over a distance, but is there a benefit to using one at a dump station? Can they be bypassed at a dump station or are you stuck with using it, simply because it's installed? We were in line behind a couple with one the other day, and it was quite a slow process compared to just pulling the handles. Forgive my ignorance, I've never owned one.

Kev
 
The main benefit of the macerator is convenience of use. You connect a 1" hose and turn on a switch. However, they are slow. In the case of the OP, they use it because the waste has to be pumped to the discharge tank and not gravity dumped.

Much easier to pull out and put back a "slinky" 1" hose than the 3" hose. Also convenient for longer distances.
 
My brother-in-law sold his Dutchstar a few years ago and gave me his macerator pump system but I've never used it. There's been about two or three times in 110k miles I could have used it, but that's all.
 
On this system the macerator is required for the Forward Black Tank due to its location forward of the rear axle and on the passenger side of the MH.  This unit is a bath and 1/2 with the 1/2 bath on the passenger side.
I have found that if you raise the front slightly when dumping the front black tank will actually empty completely, with patients.
 
Update on my macerator pump issue.  I checked the supply voltage, wire size, and discharge hose for bends, obstruction etc and no problems found.  On our current month long trip, the pump stopped pumping altogether despite the motor running fine.  Not a good situation with a full forward black tank and no gravity dump option.

I decided to remove the pump and install a drain fitting to allow gravity dumping.  A messy job but successfully completed.

I took the pump apart and found that the macerator cutter blades had come off the shaft.  Without the blades, the pump had gradually plugged up with solids until there was no flow at all.  This explains the low flow rate I had been experiencing.

I'm still working with the dealer and Winnebago to try and obtain warranty coverage for this pump failure.
 
Paul M said:
....I took the pump apart and found that the macerator cutter blades had come off the shaft.  Without the blades, the pump had gradually plugged up with solids until there was no flow at all.  This explains the low flow rate I had been experiencing.....
Click to expand...
Most excellent and thanks for the update!
 
OP here.  I wanted to provide an update on the macerator pump.  Winnebago replaced it with same Shurflow model under warranty in August and the new unit has worked flawlessly since then.  Time to empty 21 gal front black tank is consistently under 2 minutes which equates to approx 10 gpm.  Very pleased with performance.
 
Wanted some correct info along his topic. I am under the impression that our electric toilet in the Adventurer has a macerator device in its inner workings. Ours quit working and after shop repair the tech warned us about putting female foreign objects and baby wipes in there. So I think anyone with a newer Winnebago has a macerator device onboard..Correct? Merry Christmas people!!
 
I'm not familiar with the workings of an electric/macerator toilet.

My rig has regular rv toilets that drain by gravity into the black tanks.  When full, I pump the front black tank out to the sewer discharge by using the installed macerator pump located just below the tank.  To my knowledge, this arrangement is generally only factory-installed on RVs where gravity drainage cannot work due to tank location.

I would recommend that nothing other than rv-safe toilet paper be flushed in any rv toilet (especially if there is a macerator pump anywhere on the system).  Unclogging or repairing a damaged macerator pump is more involved than clearing a gravity sewer drain.
 
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