An unusual syphoning observation

[alchemysa]

I have no gutters on my house. In one corner the rainwater runs off the roof and collects in a large plastic rubbish bin. Normally i just bucket this water onto plants or the lawn but a week ago, feeling lazy, i decided to syphon it off with a 1/2" garden hose. The hose carried the water about 30 feet away up a very slight incline and terminated at a spot thats about 12" higher than the bottom of the plastic bin. As expected, the hose syphoned off most of the water from the full bin and then stopped running when the water level dropped to 12" from the bottom of the bin. (So the water level and the far end of the hose were level)

I hadnt got around to moving the hose before it rained again. I was surprised to see that the syphon emptied the bin 'automatically'. It has rained a few more times since and each time the bin empties itself except for the last 12". Maybe I'm missing something but I always thought that once a syphoning action stopped it was 'game over', but it appears that if the water level in the barrel never drops right to the bottom, and if the far end of the hose is at the correct level then a permanent 'self activating' syphoning action can be created.

Assuming this is correct I wonder if theres any practical use for this observation. Such as a no-power, no-maintenance way to keep a sump in a celler, or a car pit, empty - provided that the far end of the hose can be terminated outside at a point thats just above the elevation of the bottom of the sump, and some water can always be kept in the sump.

Maybe this is common knowledge to you guys but this 'permanent' syphon was a surprise to me.

 

[Egon]

Somehow the rainwater in the tank has to be above the top of the hose for siphoning to start without help.

Perhaps turbulence and splashing from the gutter will do this.

 

[SPYDERLK]

Maybe I'm missing something but I always thought that once a syphoning action stopped it was 'game over', but it appears that if the water level in the barrel never drops right to the bottom, and if the far end of the hose is at the correct level then a permanent 'self activating' syphoning action can be created.

Assuming this is correct I wonder if theres any practical use for this observation. Such as a no-power, no-maintenance way to keep a sump in a celler, or a car pit, empty - provided that the far end of the hose can be terminated outside at a point thats just above the elevation of the bottom of the sump, and some water can always be kept in the sump.

Maybe this is common knowledge to you guys but this 'permanent' syphon was a surprise to me.

Your original setup included a necessary condition to preserve the siphon prime during quiescence. With tubing as large as 1/2" the output end must be inclined upward by at least 1/2" at the end to prevent the water flowing slowly out by slumping. This would spoil the prime. Small tubing is resistant to this due the surface tension of the water being the prevailing force over the small D.

You will probably have good long term results with this in your barrel because of the large change in water level allowed. In a sump - maybe not. The slight vacuum in a quiescent line slowly pulls dissolved gases from the water. The bubble grows at the high point of the hose and after a fairly short time with no, or very slow flow it will grow to fill the hose diameter. A good quick water level change at this time will flush it, but if conditions remain nearly stagnant the bubble can get pretty big, completely filling many inches of the hose. Now you need a big water level change to overcome this lightweight area and flush it. Maybe more than provided for in a sump system. If you try this, use clear tubing so youll know when its time to do a preventive flush.
larry

 

[RonMar]

Sounds like both ends were able to trap the water and maintain the water in the siphon. Having the far end of the hose in a bucket would also have the same effect, and forstall evaporation lowering the level in the hose end and allowing air to enter. Flow will occur whenever the barrel level rises enough to overcome the surface tension of hte water in the hose. My irrigation system works just like this. The upper end draws from the middle of a barrel fed by an irrigation ditch at the top of my property. The pipe flows slightly uphill from there and then down to the main part of my property to several garden spigots. Once primed, it usually stays all season and feeds my sprinklers unless I do something to break the siphon and introduce air.

Another way to make a self starting siphon is as shown in the attached pic. The hose exits the side of the barrel somewhere below the top. This feedthru must be sealed. Once the barrel level raises above the hose outfeed point, water begins to flow out thru the hose and the siphon begins and will empty the barrel. I saw this on a automatic raingauge many years ago. The gauge would empty as each inch of rain collected, and the outflow would trip a microswitch and count another inch of rainfall in the display module. I have used this same principle to make automatic drip pan drains on a few occasions, the smallest being with a paper cup and some automotive vacume hose

 

[alchemysa]

Somehow the rainwater in the tank has to be above the top of the hose for siphoning to start without help.

Perhaps turbulence and splashing from the gutter will do this.

Egon. The hose clears the top of the barrel by a couple of inches so theres no way the water in the barrel can ever rise above the level of the hose. But i agree that turbulence (pressure) created when the rainwater hits the barrel could be helping to kick start the process each time.

Spyderlk and Ronmar. Yes it appears that i've just fluked upon the ingredients of a self maintaining syphon. The hose on the ground, being on a slope, continues to hold water even when the syphoning action stops.

 

[TedLaRue]

Wow. The stuff you find on this forum. SPYDERLK is explaining why an apparent permanent siphon could fail (dissolved gases?? Ah, he's a mechanical engineer.). I found that explanation very interesting.

And RonMar provides an interesting configuration for a self-starting siphon. (But RonMar, next time consider saving that kind of pic as a GIF instead of a BMP. Your picture was a 111KB BMP, but exactly the same picture is only 2KB as a GIF.)

So I learned some things tonight. Thanks to all.

 

[Egon]

For some reason I'm all confused right now?

 

[aczlan]

(But RonMar, next time consider saving that kind of pic as a GIF instead of a BMP. Your picture was a 111KB BMP, but exactly the same picture is only 2KB as a GIF.)

I second that, please save pictures either GIF or JPEG, in addition to the size difference BMP will not open in a browser and has to be opened by another program (ie: paint)
from Paint in a XP computer select GIF or Jpeg from the list of filetypes.


Aaron Z

 

[RonMar]

Sorry, that is my old school showing thru. I got in the habit years ago of sketching things in paint. I also ran win98 for a long time, and those were not options to save as like they are in the paint that now comes with XP. That is why I typically put up small drawings

 

[SPYDERLK]

For some reason I'm all confused right now?

Perhaps it is an unrelated issue.
larry