Help understanding how a siphon works?

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In summary, the image shows a classic siphon where water is transferred from one container to another. If the reservoirs are of equal height, the siphon will not work due to the water's downward momentum being greater than the uphill flow. If the reservoirs are of different height, the siphon will still work as long as the downward momentum of the water is greater than the uphill flow.
  • #1
AdamX
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Hello everybody. I am somewhat confused about how a siphon works. Attached is an image which will hopefully help me explain. In the top left corner of the image, a classic siphon is shown. My question is however directed at the second image. If i was attempting to siphon water over a fence from one swimming pool to another, and the pool reservoirs were equal in height. Would that hinder the process? Or would the siphon still work so long as the downward momentum of the water was greater than the uphill flow due to the downward section of the siphon tube being longer than the uphill section of the siphon tube?
 

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  • #2
One reservoir must be lower than the other.

You can bluff this initially by having one end of the hose lower than the other (suck water from the top of the full pool and have the hose in the bottom of the other, but once the pipe's reach equal height it will stop (and reverse).

Your description regarding "uphill / downhill" is irrelevant, it is the vertical height difference that matters only. Horizontal distance only comes into play with resistive losses, in which case the longer, the worse it is.
 
  • #3
Thank you sir i now understand.
 
  • #6
Yeah, that link has nothing to do with how a siphon works. It's simple gravity is all. The weight of the water in the tube exerts a greater amount of force on the water coming up the tube than gravity does, which sucks it up. If the two resevoirs are equal in height, then the force equalizes and water will not flow either way.
 
  • #7
As long as the water level in the source reservoir is higher than the destination reservoir, the water will flow through the siphon towards the lower reservoir. If the siphon rises above the water level in the source rreservoir, the flow will not occur if there's is an air gap at the top of the siphon. There's also a limit as to how high the siphon can rise above the water; if it's 33 feet or higher, the pressure drop versus altitude results in the water turning into vapor, and a near vacuum at the top.

The reason the water can flow upwards and then back down again is because the pressure at some height (altiitude above ground) on the "downflow" side of the siphon is lower than the pressure at the same height on the "upflow" side of the siphon, as long as the "downflow" side exits below the water level of the upper reservoir, or exits into a reservoir with a lower water level. This pressure difference results in a net flow towards the lower reservoir until the reservoirs level equalize, which will result in equal pressure versus height within the siphon on the "upflow" and "downflow" sides and the flow stops.
 
  • #8
I just want to say that you can't siphon water in a vacuum.
 
  • #10
JaredJames and Drakkith: would you like to enlighten me why am i wrong?
 

1. What is a siphon?

A siphon is a simple device used to transfer liquid from a higher point to a lower point without the use of a pump. It consists of a tube or pipe with one end placed in the liquid and the other end lower than the liquid surface.

2. How does a siphon work?

A siphon works by using atmospheric pressure to push liquid from a higher point to a lower point. When the liquid in the siphon is pulled down by gravity, it creates a vacuum that pulls the liquid up and over the top of the siphon and into the lower container.

3. What are the main components of a siphon?

The main components of a siphon are the tube or pipe, the higher container, and the lower container. The tube must be airtight and have one end in the liquid and the other end lower than the liquid surface. The higher container must be higher than the lower container to create the necessary pressure difference.

4. Can a siphon work with any type of liquid?

Yes, a siphon can work with any type of liquid as long as it is able to create a vacuum and maintain an airtight seal. However, the rate at which the liquid flows through the siphon may vary depending on the viscosity of the liquid.

5. Are there any limitations to using a siphon?

Yes, there are some limitations to using a siphon. The height difference between the two containers should not exceed a certain limit, usually around 30 feet, to maintain the necessary pressure difference. Additionally, the siphon may not work if the liquid is too viscous or if there is any air trapped in the tube.

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