Starting a siphon with flow of water/ flow of water create a negative pressure?

Question

Can you make a siphon work if you add a flow of water to the down stream portion of the siphon?

Ill rephrase it another way: The entry of the siphon is in the water of a upper tank, the tube goes up and over a wall and into another tank below the first one. If I add a flow of water to the downstream portion (after the wall before the lower tank) will the siphon start to siphon again?

last way to say it. does the downward flow of water create a negative pressure at the top of a pipe if it is vertical?

here is a related question to help

What about negative Pressure?

Answer 1

I actually did an experiment and the above answer is true!

I also did notice that once the siphon started to flow, the pump flow compounded the effect of the siphon. now the siphon is stronger with the pump than without the pump.

I also took it a step further. I made the pump, pump to the upper tank and the siphon. I was able to achieve equilibrium by kinking the flexible hose of the siphon side so that water was going to the upper tank and the lower tank at the same rate. :)

If anyone wants to try to do the calculations it might be a challenge. I used a 180 gal/hr pump with 1/2" pvc and 3/4" flexible hose. find the area of the kink part and the equilibrium flow rate?

here is a picture of the set up, left side is coming from the pump. right side is the siphon.

Answer 2

If you add a temporary flow of water that forces the air out of most of the pipe, the remaining air will spread out over the rest of the volume of the pipe as the water exits it. This will create a very low pressure in the pipe relative to the atmosphere, allowing the pressure of the atmosphere applied downward on the water in the upper tank to force the water into the pipe (because there is no longer an equal air pressure resisting this push) thus resuming the siphoning process.

Of course, atmospheric pressure isn't sufficient to push the water up more than about 30 feet, so there are limitations based on the specifications of the pipes.