close pipeline siphon connecting open canal at both the ends

[jbbr]

- I need to measure the water from an open channel getting into the pipeline siphon (1 meter dia, 800 meters long) and the discharge coming out. As the water head of the open channel at the inlet will be higher then the pipeline orifice - it looks air pockets are creating problems (resulting into vacuum). Any suggestions / advice please.
JBBR

 

[chicopee]

Were you able to remove all the air from the syphon before the air pockets developed? If so, how are air pockets introduced into the syphon? If turbulence in the flowing water within the open channel entrains air before entering the syphon then you have to have enough standing time for the air to escape before entering the syphon. Application of Bernoulli's equation in the syphon should help you figuring out the minimum amount of water in the open channel.

 

[LittleInch]

Can you provide a sketch / profile of this system and any photos you have to understand what it is you have.

How deep is the entry of the syphon?

how do you start the syphon in the first place?

What are relative levels ( this is where a sketch would work wonders), invert levels, high points, low points etc.

To avoid sedimentation ( your other post), you normally need to be flowing at > 0.75 m/sec.

what is your flow / velocity in the pipe?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[KevinNZ]

Hard to understand the problem.
Why do you need to measure flow into and out of the pipeline, they are the same.
If air is getting behind a measuring orifice plate drill a vent hole in the plate.

 

[bimr]

A continuous wave Doppler ultrasound may be used to measure the flow:

http://macemeters.com/solutions/agricultural/

 

[cvg]

you could put a parshall flume in the canal upstream and then downstream of the pipe lateral. measure the flow in both locations and subtract. a check drop or undershot gate could also be used for flow measurement in the canal.

if you dont have sufficient velocity in the siphon, than air (dissolved, bubbles) from the canal will get trapped in the siphon. your only solution to this is to increase the velocity in the siphon to move the air through.