Automated Refilling of Gravity Fed Humidifier - PROBLEM

//Mods please feel free to move this to the appropriate sub-forum, if "project guidance" is not correct.

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.

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.


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:

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?

lift the lid on your toilet.
the problem you have is that you need to maintain a level. if you have a similar float, you can do it easy.

lift the lid on your toilet.
the problem you have is that you need to maintain a level. if you have a similar float, you can do it easy.

The humidifier relies on vacuum inside the reservoir to prevent the water from flooding into the vaporization chamber. If you add any kind of pressure line into the reservoir you're going to wreck that vacuum and make an awful mess -- as OP has already seen.

Personally I can't think of any feasible method of refilling the tank automatically. Nothing that doesn't involve a vaccum pump, at least.

I dispute the premise that one has to have a vacuum.
besides, you cannot easily fill a chamber AND hold a vacuum at the same time.

a simple float on the chamber that is connected to a valve in the tank. like a lever arm. the float falls with the level, the arm lifts and more water is allowed into the resovour and the float lifts, closing the valve.

how about making something fun ? a water wheel in reverse, the wheel lifts buckets of water up and pours them into the chamber ?

OK, the original system is based on the "animal feeder" model - there is a partial vacuum in the reservoir which (exactly) balances the weight of water remaining. The vacuum is normally "replenished" by actually disconnecting the reservoir (with the outlet closed by the valve shown) and completely filling it, leaving no space for air. There is no (other) way of partially filling it; you neither need nor could employ a vacuum pump.

The suggestion to use a float valve (or a level sensor and electric valve, though no Arduino is relevant to this) on the lower pool presumes you do this instead of the original reservoir "air lock" feed - which would work. If using a pump, you need a level sensor also on the source of the water to avoid the pump running dry.

Since the original reservoir is sealed, it could be used (with the demineraliser) with gravity feed into it.