Siphoning with air in tube?

[soboness5]

So undoubtedly that title didn't explain my question very well, so let me try again:

I recently built a MLT out of a 48 qt. cooler - i'll spare you all of the details, but on the outside there is a 1/2" ball valve. I bought a 1/2"to1/2" barb to connect a 5/8" hose to the 1/2" valve.

One other critical detail - the CPVC manifold inside of the cooler lays almost flat against the bottom (slits down), and is connected to the exit hole of the cooler which is about 1" off the bottom of the cooler (about one pipe-diameter above).

Upon testing, half the time (2 out of 4 times) the water emptied to the bottom of the manifold, leaving only about 1 pint of water in my MLT - awesome! The other two times, however, the flow stopped at the bottom of the hole of the cooler, indicating there was no siphon-effect pulling the water out. All 4 tests I had the pipe dropped into the bottom of my brew kettle which was well below the bottom of the cooler, and the end of the pipe was under water after about a gallon had drained. Due to the inside diameter of the pipe, there is always air in the dead-space of the exit piping.

My question: If there is air in the pipe (not to be confused with a full-on air bubble), is a siphon possible? My guess based on my experience is 'yes'...however i'm a little perplexed as to why the siphon seemed to break 2 of the 4 times.

Any physics/fluid dynamics guru's out there have an explanation? I can take some pictures if anything is unclear. Thanks!

PS - anyone have any good tricks to sand the burrs off the inside of CPV pipes caused by slot-cutting?

 

[tchuklobrau]

It sounds to me like u dont always have the manifold connected quite right and siphon stopped where the air was entering the manifold. Not an expert but thats what it soundl like to me. As far as deburring goes i glued some sandpaper to a woden dowel worked good for me.

 

[DeafSmith]

I don't know if this applicable since I use a false bottom, not a manifold, but a trick I've found useful to clear air when transferring from my MLT to brew kettle (by gravity) is right after I get the flow started during the vorlauf, I momentarily lift up the end of the tube so that it is higher than the MLT outlet. This seems to let the liquid in the tube flow back into the MLT and push out the air from the ball valve and tubing inside the MLT. Then I lower the tube and continue - after the vorlauf, once I am draining into the kettle, I keep the outlet end of the tube submerged, especially during the siphoning at the end of the runoff.

EDIT: Actually, I lift the end of the tube as high as I can - just lifting it higher than the MLT outlet might not be sufficient, you probably need to get it higher than the liquid level in the MLT. Just for a few seconds is long enough.

 

[SKMO]

Read this a couple times and I'm still not sure what the "Pipe" is.

Making some assumptions, it sounds like an air leak to me. You can get air leaks with hot liquids that do not show up with at ambient temperatures.

Still not sure what the "pipe" is, but nobody ever accused me of being too smart.

 

[soboness5]

Read this a couple times and I'm still not sure what the "Pipe" is.

After making fun of myself for being vague in my title, I didn't do the best job of being careful with my nomenclature. 'The pipe' in my question should've been 'the tube' leading from my ball valve to the kettle. That's the only area where i'm sure there is air once I start draining, since I can see it.

I tried to not interchange 'pipe' and 'tube'...but guess I had too much home brew

 

[soboness5]

Making some assumptions, it sounds like an air leak to me. You can get air leaks with hot liquids that do not show up with at ambient temperatures.

Also - the testing was done with cold water...so i'll have to keep an eye on it at high temp.

As far as deburring goes i glued some sandpaper to a woden dowel worked good for me.

I'm going to give that a shot...otherwise the only thing I could think of is buying a super-thin file, which is the more expensive option.

I don't know if this applicable since I use a false bottom, not a manifold, but a trick I've found useful to clear air when transferring from my MLT to brew kettle (by gravity) is right after I get the flow started during the vorlauf, I momentarily lift up the end of the tube so that it is higher than the MLT outlet. This seems to let the liquid in the tube flow back into the MLT and push out the air from the ball valve and tubing inside the MLT. Then I lower the tube and continue - after the vorlauf, once I am draining into the kettle, I keep the outlet end of the tube submerged, especially during the siphoning at the end of the runoff.

EDIT: Actually, I lift the end of the tube as high as I can - just lifting it higher than the MLT outlet might not be sufficient, you probably need to get it higher than the liquid level in the MLT. Just for a few seconds is long enough.

This is interesting - i'm going to give it a shot. I was wondering if I could put my thumb over the end of the tube and lift a bit to allow the tube to fill-up right after i open the valve, then place it under-water to continue the siphon for the rest of the run-off. Will probably work for cold water...but not sure i want to dip my hand in 170 degree wort.

 

[tchuklobrau]

Dowel was $0.64. sandpaper i had here as well as the super glue. so i have $0.64 into my deburring tool