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Old 06-06-2019, 03:03   #1
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Gray water tank with electric actuators

So I just got a gray water tank for my 40 feet sailboat, but I am unsure how to hook it up. The tank comes with a macerator pump, same does the electric toilet.

I have wires run from both the gray water tank and the toilet to the main fusebox where there is a relay board located. So I was thinking about installing electric valves since I already have two switches installed for the toilet.

So single press on the left switch will run the toilet for 60s directly to the ocean, right press will run the toilet 60s to the tank. long press left button will empty the tank to the ocean with gravity, long press right button will empty the tank to the ocean with tank pump, double button long press will empty tank to shore with pump.

This was my idea, has anyone done something similiar? Attached is a sketch of how I think the setup can look like.
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Old 06-06-2019, 05:20   #2
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Re: Gray water tank with electric actuators

I believe you're actually talking about a BLACK water (toilet waste), commonly referred to as a "holding" tank. GRAY water is "galley,bath and shower water."


And as long as I have the floor for a moment...there are several flaws in your plan.

1. a 60 second toilet flush is at least twice as long as 99% of people would keep their finger on flush button or pump a manual toilet and would fill up a 40 gal. holding tank very quickly if a toilet were wired to flush that long after every use, even after urine only.

2. The entire tank must be well above waterline to be capable of dumping via gravity. And because gravity is what causes liquids to run downhill whether you want them to or not, gravity doesn't require any help from a pump. The simplicity of a gravity dump tank is its appeal. 3. If your tank isn't high enough in the boat to use gravity to dump it, an automatic timer on the macerator is not a great idea unless there will always be the same amount in the tank and the timer can be set to run only long enough to remove that amount. More in the tank, it won't be emptied...less in the tank will cause the macerator pump to run dry...and running dry "fries" the impeller in a macerator pump.

4. Dockside pumpout equipment has strong pumps that PULL waste out of a tank. A pump in the pumpout line would just create a blockage that would make pumpout impossible.

So I think you're trying to waaay over-engineer a fairly simple system...and in doing so, creating problems instead of solving 'em.


--Peggie


p.s. Sorry but I can't resist adding: Most people believe "if it ain't broke, don't fix it." But to an engineer, if it ain't broke it doesn't have enough features yet."
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Old 06-06-2019, 07:00   #3
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Re: Gray water tank with electric actuators

0 yes it is black water
1 ok, so 60s when directly to ocean, and 10s otherwise? It's just a line of code to change time when the button is pressed once..

2 tank is located 30cm above waterline

3 will run until feedback from tank level says it's empty..

4 ok, my tank came with a pump, use it or simply skip it?
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Old 06-06-2019, 07:12   #4
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Re: Gray water tank with electric actuators

Are you using a Rasberry PI to control this?
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Old 06-06-2019, 08:57   #5
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Re: Gray water tank with electric actuators

Quote:
Originally Posted by capn_billl View Post
Are you using a Rasberry PI to control this?
Yes, its running Openhab, and also control secuirty, lights, heat, keep track of engine etc...

So controlling the black water tank is easy for me, to manually operate valves requires a bit more work, because then I need to take out two drawers to get to them. And when you live on the boat its nice not to fill it up with urine.

So my idea was to use the macerator pump on the tank, just to make sure that things doesn't get stuck at the 1 inch hull through, in case something builds up in the tank.
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Old 21-06-2019, 07:31   #6
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Re: Gray water tank with electric actuators

So based on the input from @peghall I have now updated the PID for how the instalation can look like.

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