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Author Topic: Black Tank Macerator Pump Flow Rate  (Read 593 times)

Paul M

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Black Tank Macerator Pump Flow Rate
« on: May 10, 2017, 11:39:36 AM »
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
« Last Edit: June 26, 2017, 07:33:32 AM by John Canfield »
Paul & Carol
St. John's, Newfoundland, Canada
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John Hilley

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Re: Black Tank Macerator Pump Flow Rate
« Reply #1 on: May 10, 2017, 11:53:54 AM »
That's about right, one of the downsides of a macerater.
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Molaker

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Re: Black Tank Macerator Pump Flow Rate
« Reply #2 on: May 10, 2017, 01:14:13 PM »
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.
Tom & Joyce and Ditto the "don't tell her she's a dog" Westie
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Paul M

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Re: Black Tank Macerator Pump Flow Rate
« Reply #3 on: May 11, 2017, 11:20:42 AM »
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.
Paul & Carol
St. John's, Newfoundland, Canada
2014 Winnebago Vista 35F
2016 Honda Fit Toad on ACME EZE Tow Dolly

John Canfield

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Re: Black Tank Macerator Pump Flow Rate
« Reply #4 on: May 11, 2017, 04:24:20 PM »
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.
--John
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Paul M

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Re: Black Tank Macerator Pump Flow Rate
« Reply #5 on: May 12, 2017, 07:32:08 AM »
Good point John - thanks.  I will also try the pump with the engine running to ensure full battery voltage is being supplied to it.
Paul & Carol
St. John's, Newfoundland, Canada
2014 Winnebago Vista 35F
2016 Honda Fit Toad on ACME EZE Tow Dolly

Buggy-Bumpers

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Re: Black Tank Macerator Pump Flow Rate
« Reply #6 on: May 14, 2017, 11:24:24 PM »
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.
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AStravelers

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Re: Black Tank Macerator Pump Flow Rate
« Reply #7 on: May 15, 2017, 03:57:30 PM »
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. 
Al & Sharon
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John Hilley

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Re: Black Tank Macerator Pump Flow Rate
« Reply #8 on: May 15, 2017, 05:15:09 PM »
They could have routed it with sever 90 degree bends in the discharge hose.
2003 Winnebago Adventurer 38G
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Paul M

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Re: Black Tank Macerator Pump Flow Rate
« Reply #9 on: May 15, 2017, 08:21:39 PM »
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.
Paul & Carol
St. John's, Newfoundland, Canada
2014 Winnebago Vista 35F
2016 Honda Fit Toad on ACME EZE Tow Dolly

Gary RV_Wizard

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Re: Black Tank Macerator Pump Flow Rate
« Reply #10 on: May 16, 2017, 10:35:24 AM »
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.
Gary
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Kevin Means

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Re: Black Tank Macerator Pump Flow Rate
« Reply #11 on: May 16, 2017, 02:38:23 PM »
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
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John Hilley

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Re: Black Tank Macerator Pump Flow Rate
« Reply #12 on: May 16, 2017, 06:26:21 PM »
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.
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John Canfield

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Re: Black Tank Macerator Pump Flow Rate
« Reply #13 on: May 17, 2017, 07:03:17 AM »
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.
--John
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Buggy-Bumpers

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Re: Black Tank Macerator Pump Flow Rate
« Reply #14 on: May 23, 2017, 04:24:23 AM »
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.
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2014 Itasca Sunstar 35F; 2014 jeep Cherokee

Paul M

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Re: Black Tank Macerator Pump Flow Rate
« Reply #15 on: June 25, 2017, 02:10:58 PM »
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 & Carol
St. John's, Newfoundland, Canada
2014 Winnebago Vista 35F
2016 Honda Fit Toad on ACME EZE Tow Dolly

John Canfield

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Re: Black Tank Macerator Pump Flow Rate
« Reply #16 on: June 26, 2017, 07:32:53 AM »
....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.....
Most excellent and thanks for the update!
--John
2005 Horizon 40AD, 2006 Jeep Rubicon Unlimited
Our Horizon projects
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