evacuating a pipeline by using a vacuum pump 2

[aweerak]

I have to select a vacuum pump to evacuate air in a siphon system, equivalant to 15 cubic meters in one hour.The length of the 400mm dia steel pipe line is 75 m and the height difference between water intake and vacuum pump is 13m.Can anyone give me a guideline to find a suitable pump and air seperation chamber.

Aweerak

 

[bimr]

Is this a one time thing, or will the siphoning happen infrequently?

 

[chief]

why not use an eductor,if you have an air or water supply available to activate it.

Offshore Engineering&Design

 

[SteveWag]

You show the water surface as 49.25 meters and top of dam at 51.39, say 49 and 52. The lift is 49-52=3 meters. Lets add 1 more for the sensing tank, or 4 meters. This equates to about 11.5"/Hg or 300 mm/Hg. 15 CM/Hr is about 8.25 CFM. Either way, check out this link;

http://www.gastmfg.com/pdf/rotvane/70_series.pdf

1.5 HP, using the Single Function machine.

I have used PVC pipe, sometimes clear, for the chambers.

Steve

 

[cvg]

it may be easier to close valves, pump water into siphon and allow the air to exit through a vent at the high point. Then close the vent, open the valves and the siphon will start.

 

[cvg]

note that evacuating a steel pipe using a vacuum could risk collapsing the pipe. Pipes are not generally designed to support a vacuum. This is a good reason to consider priming your siphon by filling with water instead of trying to suck the air out...

 

[SteveWag]

The negative pressure on the steel pipe (pressure outside less pressure inside) is very much the same no matter how the siphon is primed. A vacuum pipe and water detection in a tank is the most reliable way, in my opinion. The drawing looks pretty well thought out.
Steve

 

[bimr]

There are a number of problems with the proposed siphon control system. This is not really a good application for a siphon either. A siphon system should be used when you want to water to flow continuously for irrigation type projects.

1. It seems that you are wasting 10 meters of static head with this scheme by placing the sump at the bottom of the slope. If you are pumping 12 hours per day, that would cost an additional $4-5,000 per year in energy costs. That means that you are wasting 20% of the power cost.

2. Your discharge line is oversized. The pump is shown as 60 l/s and you only need a 250 mm pipe to carry that flow rate.

3. It seems that submersible pumps are proposed from the schematic. This is not a good application for submersible pumps. Submersible pumps are also somewhat less energy efficient than other pumps. Submersible pumps are more commonly used on sewage, not water treatment applications.

4. How do you propose to keep the sump from overflowing? If the valves fail, the sump is going to overflow.

5. Is it possible that the sump is located in a flood zone? If the area floods, will the sump be contaminated? The electrical components would have to be mounted above flood level.

6. The valves SCV-1 and SCV-2 will not function as planned because the operating water head is so low. Throttling valves should be sized such that the flow rate is within the valve’s optimum operating range.

7. Steel piping is not going to stand up to the corrosive effects of the water in this application. You will also be susceptible to MIC (microbiologically influenced corrosion). You need disinfection as well.

8. Why not put the pumps at the top of the slope?


You need to carefully evaluate other water intake structures. Nobody would build a siphon structure like this.