Automated Refilling of Gravity Fed Humidifier *SOLUTION*

by Lcstyle on Mon Feb 10, 2014 1:20 pm

***Updated: solution works*****
See posts: p251270 and p251282

Hi all,

So I have a gravity fed humidifier. I tapped into the 1/4" Ice Maker water line and created a simple circuit with a flow meter and solenoid valve to automatically refill the tank. That all works great when the tank isn't installed onto the unit (tank is removable for refilling using regular tap).

JUST ONE LITTLE PROBLEM: the tank feeds/operates on a vacuum/gravity principle. Normally the tank maintains a vacuum, and only allows water to flow when the level gets low enough in the water reservoir underneath the tank that air is allowed to backflow into the tank, releasing some of the pressure and allowing the humidifier to feed.

Image

To accommodate automatic refilling, I drilled a hole in the tank to feed my 1/4" line in, as well as two vent holes at the top.

THAT WAS A BAD IDEA.

As soon as there is no vacuum the tank will flood the humidifier reservoir. So the tank must maintain a vacuum at all times to avoid this problem. So I tried adding one way check valves and sealing the tank again. That stopped the humidifier from flooding. Then I realized that even if I release the pressure and maintain a vacuum while filling using one way check valves, because the tank's valve at the bottom is open while the tank is installed in the unit, water will just run out and overflow anyways, and the water level in the tank will never rise to full, instead it will just overflow.

Cap with valve automatically opens when placed onto unit, allowing water to feed from tank into reservoir well during normal operation:
Image

So now I need to seal off the tank from the rest of the unit while refilling.

Whatever I do, it's going to have to be done inside the tank itself. I am thinking of sealing off the tanks feed valve at the bottom and then using a float valve that would cut off the flow from the tank to the reservoir when the water level in the tank gets low, and only open it again when the tank's water level is topped off. That seems to be the easiest solution.

Any suggestions?


***Updated: solution works***** this post: viewtopic.php?f=8&t=49627&start=15#p251270
Last edited by Lcstyle on Sat Feb 15, 2014 10:56 pm, edited 5 times in total.
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by jcgoodman on Mon Feb 10, 2014 3:11 pm

Lcstyle wrote:Any suggestions?


Remove the tank entirely and make your refill circuit work on the small reservoir inside the humidifier?
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by Lcstyle on Mon Feb 10, 2014 3:27 pm

jcgoodman wrote:
Lcstyle wrote:Any suggestions?


Remove the tank entirely and make your refill circuit work on the small reservoir inside the humidifier?


The reservoir is so small, its meant as just an immediate feed platform for the ultrasonic transducer. That would cause the solenoid to have to constantly turn on and off, also the flow rate is too high, and flow sensor not accurate enough to dispense such small amounts.
Thanks for reading through and your suggestion though :D

Here are pics of the platform:
Attachments
20140210_151822.jpg
reservoir tank and humidifier
20140210_151822.jpg (127.86 KiB) Viewed 195 times
20140210_151746.jpg
humidifier platform
20140210_151746.jpg (155.71 KiB) Viewed 195 times
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by 1chicagodave on Mon Feb 10, 2014 3:27 pm

What if you connected a pump on the top of the tank to 'suck' the air out of it, maintaining negative pressure, and allowing water to flow in when needed....then sealing it off again when full? As long as pressure in tank is less than atmospheric pressure (and/or gravity)....it should prevent water from escaping the reservoir and into the well.

*Not sure what might work for this. Some calculations and testing may be necessary. :?
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by Lcstyle on Mon Feb 10, 2014 3:34 pm

1chicagodave wrote:What if you connected a pump on the top of the tank to 'suck' the air out of it, maintaining negative pressure, and allowing water to flow in when needed....then sealing it off again when full? As long as pressure in tank is less than atmospheric pressure (and/or gravity)....it should prevent water from escaping the reservoir and into the well.

*Not sure what might work for this. Some calculations and testing may be necessary. :?


I thought about this option intensely, if I can pull a vacuum on the tank in the air space at the top, it might work, though I have no idea what kind of math would be required here to calculate how much vacuum I would need in inches to defeat gravity flow of water column. What would that math calculation entail? surface area, volume of liquid, dimensions of container holding body of water? A cool experiment indeed, however, I am thinking of going the easier option and just sealing off the bottom valve using a piece of pvc tubing and then attaching a float valve to that assembly in reverse, so that when the reservoir is empty it closes, and when full it opens again, allowing flow.

Will probably try both, test, and report results.
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by adafruit_support_bill on Mon Feb 10, 2014 3:55 pm

The reservoir is so small, its meant as just an immediate feed platform for the ultrasonic transducer. That would cause the solenoid to have to constantly turn on and off, also the flow rate is too high, and flow sensor not accurate enough to dispense such small amounts.

I think that is a solvable problem. First, I would add an adjustable valve to restrict the flow. Then I would replace the flow sensor with a level sensor. It could be a small float that rides up & down in the inlet tube and blocks a photo-interrupter sensor when full.
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by Zener on Mon Feb 10, 2014 4:02 pm

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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by Lcstyle on Mon Feb 10, 2014 4:16 pm



You couldn't because it would still result in the overflow. The only thing keeping the fluid from leaking out is the vacuum.
When the water gets low enough, air backflows into the reservoir allowing more to feed.

You can test this for yourself by putting a hole in the lid of a glass jar, filling the glass jar 3/4 of the way full.
Turn the jar upside down and place it just far enough into a volume of water to seal the hole in the lid.
Slowly lift the jar out of the water in a perfectly vertical movement, when the opening in the lid reaches air, it will suck air and allow water to flow out.

If you try to fill the jar from the top via a tube inserted through a sealed hole, it will increase the pressure of the air space inside the container (decrease the vacuum) and water will come out. The water level may rise, fall, or stay the same, (probably depends on flow rate of liquid), though I am not sure because I haven't performed this test myself. I am not a physics person so I could definitely be wrong, yet this is what I've deduced the behavior to be from my observations so far.
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by Lcstyle on Mon Feb 10, 2014 4:19 pm

adafruit_support_bill wrote:
The reservoir is so small, its meant as just an immediate feed platform for the ultrasonic transducer. That would cause the solenoid to have to constantly turn on and off, also the flow rate is too high, and flow sensor not accurate enough to dispense such small amounts.

I think that is a solvable problem. First, I would add an adjustable valve to restrict the flow. Then I would replace the flow sensor with a level sensor. It could be a small float that rides up & down in the inlet tube and blocks a photo-interrupter sensor when full.


I think I'd rather keep my original idea (and refill the reservoir) and struggle with the problems at hand. I'd like to retain the OEM look and finish of the product I'm working on.
Also, at this point It's more than just a project, now it's becoming a challenge and a learning experience.

That said, thank you for the remarks, which I believe certainly could work.
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by 1chicagodave on Mon Feb 10, 2014 5:06 pm

(I have a similar humidifier)

Just had another thought....

If you can get underneath where the reservoir sits - there's that plastic 'pin' which pushes the plunger/valve up when reservoir is inserted. If that could be replaced with solenoid or 'servo-plunger' (I just made that up), you may be able to lower it, thus closing the plunger/drain whenever it's time to refill.

....this could probably be done with magnets alone (push to open, pull to close) to help maintain water-proofness.
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by Lcstyle on Mon Feb 10, 2014 5:16 pm

1chicagodave wrote:(I have a similar humidifier)

Just had another thought....

If you can get underneath where the reservoir sits - there's that plastic 'pin' which pushes the plunger/valve up when reservoir is inserted. If that could be replaced with solenoid or 'servo-plunger' (I just made that up), you may be able to lower it, thus closing the plunger/drain whenever it's time to refill.

....this could probably be done with magnets alone (push to open, pull to close) to help maintain water-proofness.


DID YOU SAY MAGNETS?
http://www.youtube.com/watch?v=EwVDDxoKBk4&hd=1

But seriously, I have performed the following test:
plastic bottle, made hole in bottom, feed water line into this hole, sealed pretty tight.
Plastic Pan, with a level of water in it.
Filled plastic bottle about halfway.

Placed mouth of plastic bottle into water in plastic pan, not touching the bottom, just on the surface to seal.
Result: Volume of liquid holds.
Great!
Next: Turn valve on to feed line.

Guess what happens? Even at full flow rate, volume of liquid remains constant in container.
This is probably obvious to a lot of people but, I think if I pull a vacuum on the bottle the liquid level will rise instead.
we want to pull a slightly negative pressure, just over what would be considered constant during filling.

Option 1: (will work and you can vary the length of the pvc tube so that the float sits at just the right levels)
required : 1 way air release "check valve" in reservoir.
place a piece of PVC tube over the reservoir cap and valve to seal it off from water in tank, then attach this valve (in inverted configuration, so that float closes when empty, and opens when full)
http://www.usplastic.com/catalog/item.a ... &catid=569
OR
http://www.usplastic.com/catalog/item.aspx?itemid=23234

Seal off by using some pvc pipe and pvc cement.

Problem with this method? the valve body inlet may rest too high from the floor of the tank to allow usage of entire volume of liquid in reservoir.

Option 2: (my preferred method that hopefully will work: haven't tested yet).
Pull a vacuum on the reservoir and fill.
If the pressure level remains constant or negative while filling, you should see the fluid level rise without overflowing the tank.
This option obviously wouldn't require a 1 way check valve to bleed air pressure.

I will test both and return results.
Last edited by Lcstyle on Mon Feb 10, 2014 6:15 pm, edited 1 time in total.
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by jcgoodman on Mon Feb 10, 2014 6:01 pm

As everyone's starting to realize, the problem is not just that there's not enough water in the tank, it's that there's too much air. Any solution must both add water and remove air simultaneously: you're going to need a suction pump.

Not that I think you should use one: I think removing the tank and installing a little bitty float sensor in the reservoir is the only sane way to go. If the reservoir isn't deep enough, put the sensor in a a U-tube. I know you want to preserve the look of the original equipment, but if you can actually pull that off you're a better builder than I. Whenever I try something like this, I know it's going to look like the Borg mothership when I'm done with it.

I say, the best use for the water tank is as a convenient case to pack the electronics and valves in. Preferably with a gratuitous blinky blue LED display inside.

But that's just me. Good luck!
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by Lcstyle on Mon Feb 10, 2014 6:05 pm

jcgoodman wrote:As everyone's starting to realize, the problem is not just that there's not enough water in the tank, it's that there's too much air. Any solution must both add water and remove air simultaneously: you're going to need a suction pump.

Not that I think you should use one: I think removing the tank and installing a little bitty float sensor in the reservoir is the only sane way to go. If the reservoir isn't deep enough, put the sensor in a a U-tube. I know you want to preserve the look of the original equipment, but if you can actually pull that off you're a better builder than I. Whenever I try something like this, I know it's going to look like the Borg mothership when I'm done with it.

I say, the best use for the water tank is as a convenient case to pack the electronics and valves in. Preferably with a gratuitous blinky blue LED display inside.

But that's just me. Good luck!


You're not too far off from the truth here, problem is I'd rather not have a solenoid opening and closing that often, as the reservoir area for the transducer is tiny! How often would it need to open close? A LOT.

The other solution is to use a float valve, but, that isn't cool :(
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by adafruit_support_bill on Mon Feb 10, 2014 6:45 pm

Preferably with a gratuitous blinky blue LED display inside.

The most important part of any project. :D
How often would it need to open close?

That depends on the flow rate - which could be reduced to a trickle with a small aquarium valve.
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Re: Automated Refilling of Gravity Fed Humidifier - PROBLEM

by Zener on Mon Feb 10, 2014 9:22 pm

jcgoodman wrote:... installing a little bitty float sensor in the reservoir is the only sane way to go. If the reservoir isn't deep enough, put the sensor in a a U-tube.

I think this is along the lines of my latest idea. But I don't know the nature of the "reservoir" or the U-tube. I do see the second, lower water level in the first picture, and I am guessing that is the reservoir. It seems to me the thing is basically similar to this:

http://www.ebay.com/itm/PETMATE-CAFE-WATERER-DRINK-WATER-DISPENSER-3-4-GALLON-PET-EASY-CLEAN-PEARL-TAN-/201027826662?pt=Dog_Dishes_Feeders_and_Fountains&hash=item2ece3133e6

For example, if you wanted to add water to this, you could try adding to the tank, and you would have the problems you encountered - the dish would overflow. Or you could just add to the dish itself. Then as jcgoodman pointed out, the tank itself isn't doing much.
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