Siphon theory

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Old 12-10-04, 07:44 AM
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Siphon theory

Need info on how a siphon works in order to determine placement of discharge of an exterior drainage pipe.

Can/does a siphon continue to work, once started, if the discharge end is higher than the intake end, if (1) the discharge end is lower than the crest point of the siphon and (2) the volume between the crest and the discharge end is greater than the volume betwen the crest and the intake end. Thus the greater volume on the discharge side of the crest causes the siphon continue to pull the lesser volume on the intake side of the crest?

I am presently using a hose to siphon water from one location to another but a drainage pipe would be better. I would confidently place the discharge of the drainage pipe the same place as the hose discharge if I could be certain the hose discharge is actually lower than the hose intake. (The hose setup may be as described above, most of the hose is between the crest and the discharge side.) However, if a siphon can continue to function even if the intake is lower than the discharge, as described above, then my hose discharge location could be higher than the intake, and thus not a good place to put the drainpipe discharge.

I wasn't sure where to post this, so I put where the water flow experts likely are. Thanks for any replies.
 
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Old 12-10-04, 08:08 AM
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A siphon will not continue to work, once started, if the discharge end is higher than the intake end.

If you replace the hose with a pipe, how are you going to get the siphon started each time it is needed?
 
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Old 12-10-04, 08:23 AM
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Thanks for the info. The drainage pipe would go underground, flowing downhill, whereas the hose presently is routed on the ground surface with a crest between the intake and the discharge.
 
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Old 12-10-04, 02:41 PM
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So, If you replace the hose with a pipe, how are you going to get the siphon started each time it is needed? Are you going to dig up the pipe to suck on it, put an in-line vacuum pump, or what?

There are no auto-syphons that I know of.
 
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Old 12-13-04, 04:55 AM
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Well, if the discharge end is lower than the intake end, and the pipe is a straight line, then I assume gravity would cause the water to flow.

I raised my initial question because it appeared to me that when using the hose to siphon that the discharge end was not lower than the intake although it was lower than the crest of the siphon, and maybe 80% of the hose was bewteen the crest and the discharge end. If a siphon could actually work under these conditions, then it would not work to place a the underground drainage pipe discharge at this same location (I did not want to figure this out after installing the drainage pipe). Since you tell me that the discharge end of a siphon must be lower than the intake then I can confidently plan to put the discharge end of the pipe where the hose discharge is, and know it is all downhill.

Hope this clears it up for you, sorry for any confusion. Thanks for your help.
 
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Old 12-13-04, 05:20 AM
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A siphon will draw water up over a crest, but the siphon action stops when the water level at the 'supply' side is equal or lower that the discharge end.
 
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Old 12-13-04, 05:46 AM
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Originally Posted by dave houlihan
Well, if the discharge end is lower than the intake end, and the pipe is a straight line, then I assume gravity would cause the water to flow.

Hope this clears it up for you, sorry for any confusion. Thanks for your help.
What you are describing is a drain pipe. But your original post was about a siphon. Water will not flow uphill, without mechanical assistance, unless it is being siphoned. You either have to have a vacuum on the discharge end to suck water over the crest, or you must have pressure on the intake end to force water over the crest.

It would surely clarify this thread if you would post a description of what you are trying to do, i.e. what problem are you trying to solve?
 
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Old 09-29-10, 08:31 AM
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The discharge end (where the liquid comes out) MUST be lower than the liquid free surface on the intake end for a siphon to continue flowing. The entrance of the intake may be lower than the exit but the liquid free surface MUST be higher than the exit. This means it does not matter how far down into the liquid you stick the entrance end. It's only a matter where the free surface is.

Simply put if the elevation of the exit is lower than the elevation of the free surface of that which you want to drain, then the siphon will flow.
 
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Old 09-29-10, 10:04 AM
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Thanks for clarifying this nearly 6 year old post
 
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