Bulkhead/In-line Replenishment Snag...
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Old 09-25-2005, 03:56 PM   #1
scolley
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Bulkhead/In-line Replenishment Snag...


For a long time I've been lusting after a form of water replenishment that doesn't require overflows. Something that would provide not only top-off, but could eliminate large water changes. For instance, if my math is right, if I had something that could automatically drain then add just 1 gallon to my 75g, 7 times a day, I would be turning over water at the same rate as a weekly 50% water change - no more water changes! And auto top-off just happens as a byproduct.

Great idea IMO - but apparently tough to accomplish without some kind of overflow.

When I set up my current tank, I drilled bulkheads in the bottom, and left one unused to help with this problem. I went and bought a couple of these pressure switches to help. The idea was easy...

Leave a bulkhead open, connected to the pressure switch. The switch would be configured in a normally-open configuration, and would only close when the pressure (water level) was below the desired height (pressure). Then it's just a matter of putting a normally closed solenoid in-line, and on a timer to drain water returning to the tank for a few minutes. When that's done, have another timer power up the pressure switch, which would detect a low pressure condition, and would turn on a pump from a reservoir until the appropriate water level switched it off.

I bought two of the pressure switches so I could put them in series, so that if either of them thought the water was high enough, the new water shuts off. Redundance seemed like a good idea.

I've started testing these switches, and they do a pretty good job. In a test setup, over many trials, their variance in shutting off at a consistent water height is about 1/4". Good enough if for me, if used redundantly.

I'm writing because I've run into a snag though...

The pressure switches detect a "full" condition very well. The problem is state change. Once they detect the "full" condition, they open the circuit, and the circuit remains open until the pressure drops much, much lower. In my case, they won't close again until half the water is out of the tank, and then they faithfully turn on until they are within 1/4" (+/-) of the desired water height.

Bummer. So much for losing a gallon at a time, and letting these things control the top off.

I've come up with a solution, but it's so complicated, I'm not even going to post it. Too prone to failure. Any ideas? I'm stumped.
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Old 09-25-2005, 04:51 PM   #2
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So what you're looking for is a way for Mr. Bass to flush the toilet once a day? Sorry, couldn't resist.

I know one of old-time members of the SFBAAPS has a fully automated water changing system plumbed in. But his is a full out water change, not a mini one that you're looking for.
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Old 09-25-2005, 05:11 PM   #3
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Yeah, thanks. This would would do a water change too. The amount of pressure drop to get these switches to switch state (or reset) is almost exactly the number of inches of water my tank loses on a 50% water change - by coincidence.

But if I used this just for water change, the auto-top-off capability goes away. And then you have to get involved with using Prime - so it's not really unattended. With the smaller changes there are lots of possibilities, like no prime at all due to the small amounts. Or having a small (20g?) aging tank hooked up to the house water supply.
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Old 09-25-2005, 06:36 PM   #4
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Try a peristaltic doseing pump that can handle two lines. Set one in, one out so that the volume is conserved and volume is set by the time opperated. 50 % a day may not be bad though if your water is cheap...
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Old 09-25-2005, 07:02 PM   #5
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Quote:
Originally Posted by BlueRam
Try a peristaltic dosing pump that can handle two lines. Set one in, one out so that the volume is conserved and volume is set by the time opperated. 50 % a day may not be bad though if your water is cheap...
That's a great idea Blueram. But you loose auto top-off. But it is devilishly simple, and tempting...

But idea about more frequent water change is an idea though. Water is cheap here. And truth be told, in the winter (when it's so dry inside due the heaters) top-off isn't needed my often than 3 times a week. I'll bet 3 50% water changes wouldn't wast much more water than using the massively wasteful python I'm using today.

Would causes massive swings in ferts though. But I could set a different timing for my dosing pumps on "water change" days. Hmmm.....
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Old 09-25-2005, 09:27 PM   #6
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I thougt the dosing pump does "top off" service.

You might be able to rig somethink like this in the cypress stump:
http://www.bluelineaquatics.com/products/topoff_system/

My sink is lower than my tank, so I use* the python to start and then turn off the tap and let it go. *now I just mouth-syphon and dump the open end into the tub which is even lower...

Very expensive example:
http://www.kc-denmark.dk/public_html...altic_pump.htm
Check medical surplus...
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Old 09-25-2005, 09:59 PM   #7
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Quote:
Originally Posted by BlueRam
I thougt the dosing pump does "top off" service.
Not for me... and my hat's off to people trying to make that work. My evaporation rate is way to inconsistent for me to try that. All depends on the heat, and that varies significantly.



Quote:
Originally Posted by BlueRam
You might be able to rig somethink like this in the cypress stump:
http://www.bluelineaquatics.com/products/topoff_system/
Seen those. Thanks! What I'm trying to do now is quite similar, except I've got a water pressure sensor at the bottom of a tube that passes through the bottom of the tank, rather than something over the top with an air pressure sensing on top. I suppose if I had set it up initially, I could get one of those bulkhead airline connectors to make that work. But messing with bulkheads now means tearing down the tank. Not an option for a year or so.



Quote:
Originally Posted by BlueRam
My sink is lower than my tank, so I use* the python to start and then turn off the tap and let it go.
Not an option for me I'm afraid... sink's too high.



Quote:
Originally Posted by BlueRam
Yeah, massively expensive! The dual perstaltic idea makes me uncomfortable, due to the "some of the water that just went in a second ago, is in the water going out now" problem. Kind of clouds the question of just how much turnover you are really seeing.



Thanks for the ideas though. Any ideas on how to get what I've got workind? How to get beyond that 10" of water state-cycling problem?
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Old 09-25-2005, 10:17 PM   #8
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Can you set one (or a pair) as high and the other low. Something like a drop of 1" turns the pump on until the high (the one you have rigged) turns it off?

Or are you saying it takes 10" for the high to sense.

You might be able to pump water in and use the high to open the bulkhead?
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Old 09-25-2005, 10:55 PM   #9
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First, they can set to be either normally open, or normally closed. In fact, you could put two circuits on one at the same time, and when an appropriate pressure was reached, the open circuit would close, and the other the reverse. They are pretty flexible. And pretty accurate.

Here's the problem...

Let's say it knows that the pressure threshold has not been exceeded (water column not high enough) and it closed a circuit, turning on a pump to put water in the tank. The pump will remain on until the appropriate height is reached, then the switch opens the circuit, and the pump turns off.

On the next day, you drain a bit of water out of the tank, and assume the switch will close the circuit again and start the pump to replenish water again. Nope. Once that that pressure sensor opened the circuit (the day before) it will not close it again until the water drops about 10"!

So yeah, I've figured out a kludgey plumbing mechanism to fool it into thinking that has happened. But it includes solenoids, drains, and just way too much wackiness. There has to be a simpler way.

I've thought about using both of them, as you suggest, one as a high, the other as a low... but it doesn't really work, I don't think. No matter what you rig one to do, turn on or off, at a given pressure, you still have to lower the pressure about 10", where it switches to the opposite state (off to on, or on to off) to get it to do that trick again.

It could be the solution to my problem is a refund.
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Old 09-26-2005, 03:26 AM   #10
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Float Switches!

One (or two for redundancy) wired normaly open at the top of the tank that activates when the water level drops. Instead of relying on volume and pressure the switch would activate simply upon water heighth. Auto top offs too!

Then possibly you could use your pressure switch on a timer that would drain water to a certain level. As long as you could get water out of the tank faster than you could get it in you wouldnt be wasting too much water.
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Old 09-26-2005, 03:38 AM   #11
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Quote:
Originally Posted by JimmyYahoo
Float Switches!

One (or two for redundancy) wired normaly open at the top of the tank that activates when the water level drops. Instead of relying on volume and pressure the switch would activate simply upon water heighth. Auto top offs too!

Then possibly you could use your pressure switch on a timer that would drain water to a certain level. As long as you could get water out of the tank faster than you could get it in you wouldnt be wasting too much water.
Yup...gnatster has a similar method employed on one of his tanks. He has his sump setup with a float switch so when he drains it it automatically fills up with water from his RO unit until it hits the switch again.
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Old 09-26-2005, 05:00 AM   #12
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Yup. Thanks guys. Float switches are the obvious answer. I suppose what's not so obvious to everyone is that I can't use them. I'm on an aggressive campaign to eliminate anything that hangs over the side of the tank. And I want any equipment in the tank to be invisible. That's why I'm going to all this silly pressure switch trouble.

And a float switch either has wiring hanging over the side (against the rules for me) or it could be threaded up through a bulkhead, but even then, it will be hanging out at the surface for all to see (again, against the rules for me).

Thanks for the suggestions though. It would be a lot easier if I'd back off on the aesthetics!
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Last edited by scolley; 09-26-2005 at 11:06 AM..
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Old 09-26-2005, 05:10 AM   #13
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aha, seemed to simple. Lookin at your tank now i see the clean look your goin for, and nice job of attaining that as well, thats a great lookin tank.
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Old 09-26-2005, 11:16 AM   #14
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Thanks JimmyYahoo!


WOW! I may have just figured something out...
I could stick a "T" in the pressurized water line just over the switch. Then hook a little air-pump up to the T. Just before powering up the switch (to turn on a tank filling pump), I could turn on the air pump for minute, just long enough to fill the tube with air, and hopefully reset the switch.

Kinda kludgey, and would send a few bubbles out the manifold, but it might work!
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Old 09-28-2005, 02:42 PM   #15
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Default Pressure switch range

If the switch is resetting after a ten inch drop that is pretty good for a switch of that type. The 10 inch drop is only a change of .4 psi. A quality
industrial switch that costs about 300 will only get you down to a five inch
dead band.
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