Poor Man's Float Valve?

[Chucker]

I've got a CPR MRT, and want to upgrade the lighting on it. I've been toying with the idea of putting a 70w MH over it. If I put a halide over the MRT, it's gonna evap like a sonuvabitch. (They have a cover to lower the evap rate, but I'd prefer to leave it off for cooling purposes.) I'll need careful attention to topoff, but that's kind of a PITA, especially since salinty would vary widely if I just dump in the 1/4 gallon it might evap every day when I get home from work. Here's what I've come up with-

I can take my current evap vessel (old 1 gallon juice bottle), and place it on the top shelf of my desk to get a nice gravity feed. Tap the bottom of it to fit a barb, and put a piece of airline tubing on it. Drill a small hole in the cap so I don't create a vacuum. Run the airline down to the skimmer on the intake side where the water level normally drops from evap. Take a nice stiff 6" piece of fishing line (like 50 lb. test), and tie a big knot in the end of it. Insert the line through a hole in a small styrofoam block, and then thread it up the tubing.

The block can float freely in the intake section, and as water level drops, the styrofoam will unseal from the end of the airline, allowing water to flow to top off. Once the level is reached, the foam will seal off the airline again.

Problems I see-

Ensuring a good seal between the airline and the foam. Possibly add a small rubber ring gasket around the airline to help it seal better.

Skimmer tuning- if I add FW to the intake side, the skimmer normally goes nuts, and skims off really foamy water, so I lose what I topped off. Not really sure about solving this one. I can hope that the top off goes in slow enough that it won't really make any difference.

Flow around the block to the powerhead running the skimmer. Trial and error experimenting with block size.

Comments and suggestions?

 

[Enkidu]

my first thought is that you have to make sure the jug isn't too high above the water line. You don't want the effect of the pressure to be greater than the bouyant force of the foam block.

 

[Chucker]

Ahh, something I hadn't even considered.... Kinda sucks, because the only other shelf I have is below tank level.

 

[MadMorf]

The height of the jug isn't the problem...

The amount of water in it is....

The only thing the height will do is add more length to the tubing and add the weight of water in the tube...

If you find that the float won't stay closed with a full jug try lesser amounts of water...

Something else you might try:
If the lid on the jug has a tight seal just run the tube into the tank without a float. The vacuum (relative to atmospheric pressure) at the top of the jug will keep the water inside as long as the end of the tube is under water. When the water level drops air will go up the tube and start to equalize the pressure allowing some water to come out...
Works just like a weekend watering dish for your dog or cat...
And, no moving parts...

Chuck

 

[fishfarmer]

Madmorf's has a good idea with the vacuum topoff. Here's a bit of advice if you go that route. You will want a fairly large diameter tube coming out of the jug, airline tubing won't work. Try 1/2 to 3/4 inch. It also will probably need to be a straight shot from the jug to the water level, no 90 degree angles, which may cause airlocks.

My 4 gallon kalk doser topoff works on this principle. I have a valve fitting coming from the bottom of the jug, with 3/4" tubing going to the level of my sump. The unit had a sealable top and sits next to my sump. Works great.

 

[Kenzy]

How much space is in a MRT(sump part). I've seen some furnace humidifier float valves that are smaller than a Kent float valve (and a fraction of the cost for the same !@## thing)
that might be able to fit in a MRT. IMO this would be more reliable and less fiddley. Simply plumb it to a bucket of what ever size and let gravity do its thing.

Just a thought.

 

[Chucker]

Kenzy, the float valve would have to fit in a space that is less than 2.5" wide, 3" long, and 4" deep. I'm going to have a friend build me a nice acrylic topoff, and make my life simple ;-)