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Old 07-29-2004, 12:58 PM   #1
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1973 31' Sovereign
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Valve before or after macerator pump?

I am giving serious thought to installing a macerator pump. The input side would be 3" and the output side is 1". Is there any reason that a dump valve on the 1" output side wouldn't be just as good as a dump valve on the 3" side? It seems like it should be less expensive. As it turns out it would also be more readily accessible in my case. The only downside I can think of is that the macerator would have fluid in most of the time rather than having a chance to dry out from time to time. Is this an issue? Also I see that dump valves seem to be readily available for 3" and 1-1/2" but what about for 1"? Would the valve have to be especially for a dump valve or could it be a typical 1" plumbing valve?

Thanks,

Malcolm
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Old 07-29-2004, 01:03 PM   #2
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My understanding is that there are two types of macerator available, one for submerged install. and one for non submerged

The ones that are normally sold for RV use are not the ones designed for submerged use. If the impeller is kept in a submerged state they will fail or the seals will in time. All of the documentation I have read (RV Models) say to rinse and llow to dry after each use. Last thing you want to do is have to replace a submerged pump with a full tank

Look at the models designed for marine use. These are normally designed to be installed before a valve.
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Old 07-29-2004, 01:42 PM   #3
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My plan is to use one after an electric dump valve. That way when, not if, it needs servicing there is no problem with stuff. Also don't have to get under ot turn or open anything. I think standard parts will be less expensive. The standard plumbing value will introduce further restriction in the line I.
When in doubt you could ask the company that makes them.
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Old 07-29-2004, 01:56 PM   #4
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I wasn't aware of any submerged or non-submerged issues with the Jabsco macerator pump. Is there another brand?
Regardless, I would either have a valve ahead of the pump, or a capped tee, so that there is a back-up way to empty and rinse the tank, if you need to remove the pump.
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Old 07-29-2004, 02:37 PM   #5
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Here's what I did on the MoHo

I tee'd into the dump line after both of the Thedford valves.

I also installed a valve at the macreator outlet. All the valves and the caps insure I don't get any "Brown drips on my white shoes".
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Old 07-29-2004, 03:08 PM   #6
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Good point about service...

That is a good point about being able to shut off the tank side if I need to remove the macerator for any reason. If I only have one valve it sounds like it should be on the tank side of the macerator rather than on the output side.

On another note I notice that the Jabsco macerator pumps are available with 3" input and in versions that neck down to something like 1-1/2" input. It looks like the actual input to the pump is in the neigborhood of 1-1/2". So the question is does it really make any difference what size pipe I have from the black water tank to the macerator?

Also I have been looking at various tank options to fit the space that I want to install my tank. There are some holding tanks that have a built in slope which, of course, seems like a good idea. Other tanks of various kinds are available that do not have a built in slope. Some of them seem to be holding tanks and some are just rectangular tanks (such as water tanks). The original BW tank on my unit was above the floor and did not have a built in slope as far as I know. The question is how much does the slope matter when using a macerator pump? Would there be any serious issues using a flat bottom tank other than the fact that I may not be able to get the last 1/4" of water out of it? What if I used a flat bottom tank and installed it at a slight angle for better drainage? By the way the main reasons for considering a flat bottom tank is cost savings, better fit in the space that I have available and the option to put the fittings anywhere I want them.

Malcolm
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Old 07-29-2004, 03:44 PM   #7
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Inlet, outlet sizes, mounting, tank drainage.

Most of the Jabsco pumps have a 1 1/2" NPT male fitting to attach to. The outlets are 1" barbed. I stuck with 1" ID on the outlet since I carry a 20 foot discharge line. You could get by with a smaller ID, but don't go too small or too long, or the pump will overload (hopefully blow a fuse, and not burn out the motor).

On the mounting, most all of the Jabsco Marine installations I remember the inlets are constantly flooded. I don't think it makes any difference at all to the seals. I honestly do not remember any warning with the pump to avoid a constantly flooded suction. -- Mine stays flooded.

If you place the center line of the pump slightly below the bottom of the tank, no slope would be required. I have had no issues with the macerator pump set up, and am quite happy with it. Only down side the discharge of the pump is slightly below axel height, but whatever is not protected from road gators is mostly rubber, so not a lot is likely to get damaged.

FWIW, I would avoid a single tank, and manifold the discharge of your existing BW tank into the pump with a good valve, along with a valve on the discharge of the Gray Water tank. Both tanks staying separate from one another make for a much "cleaner" and sanitary installation, besides offering a bunch more versatility.
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Old 07-29-2004, 05:20 PM   #8
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Malcolm,
I think you're right about the inlets. You can buy one with no inlet pipe, where the OD of the impeller housing is 3" and clamps directing into a 3" Fernco type boot, or the 1 1/2" fitting. I think I would prefer the 3" design. The inlet tube might restrict the flow of some of the 'solids', especially if you eat a lot of cheese.
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