Siphon

[Thuba]

l have a tank 2m ×2m×2m. So my volume is 8m3. l want to be able to to siphon the liquid at 16m3/h, using it as a purge line for my hotwell. l could have installed a pipe and a valve at a bottom of the tank, but the problem this will need a shutdown. My question is there any equation to calculate the right pipe diameter and height of the siphon. Attached is the schematic diagram

 

[pierreick]

How will you create the siphon? driving force?
Pierre

 

[LittleInch]

Height of the top part of the syphon just needs to be less than 7m above the lowest level of the water.

In terms of pipe there are any online equations size your pipe.
One issueyiu face is that if the end point of the drain is less than 7 or 8m below the bottom of the tank, your driving head keeps cha ging as the water level goes down unless you're, keeping the level constant.

Unless you put a non return valve on the inlet into the pipe you will never fill the pipe with water to create the syphon.... Plus you need a valve on the primer to create the syphon.

 

[crshears]

If a valve is placed at the outlet and closed during priming, cannot an aspirator be used at the top of the siphon to extract the contained air? This would obviate the need for a foot valve at the inlet.

 

[LittleInch]

If a valve is placed at the outlet and closed during priming, cannot an aspirator be used at the top of the siphon to extract the contained air? This would obviate the need for a foot valve at the inlet.

Yes, but a bucket of water is a lot cheaper.... And you wouldn't fill the leg downstream of the high point...

You have to assume the pipe is empty at the start.

Aspirator are OK when used with pump suction, not syphons.

 

[crshears]

LittleInch: And you wouldn't fill the leg downstream of the high point...

Why not?

If lower valve is closed and aspirator draws water up from the upper reservoir, will it not spill over the saddle of the apogee and prime the downstream side as well?

Or am I missing something?

 

[LittleInch]

Well to be fair it might, but it will only do this really quite slowly and is not the normal way people fill syphons like this. Also its really difficult to know when the downstream bit has completely filled.

It works on pump suction lines for sure, but syphons are better filled from the top.

A lot depends on the relative volume and where the syphon is. If it is in say the first 10% of the line then its a long time to drag liquid up to the high point then allow it to dribble over the high point, which may not be a short sharp peak, into the downstream section.