How to prevent siphon 1

[SA07]

Hi
We have 4 pipes of raw water coming from different sources which enter a small tank/ filter and then the overflow fall into a 1000 m3 tank. Not all pipes bring water at the same time. We have noticed that siphon occurs sometimes in an empty pipe. Is there a method to prevent this ? Is there a small device which can be installed on each pipe which can prevent this?

The pipes size varies from 200 to 400 mm. Thks

 

[LittleInch]

usually a vacuum breaker, but if you can provide a schematic we might be able to understand your problem better.

Difficult to see how you get a syphon in an empty pipe??

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

 

[hydtools]

Are you, in fact, getting backflow into the empty pipe? May need a swing check valve.

Ted

 

[SA07]

Yes it seems we are sometimes getting backflow in the empty pipe. 2 of the pipes can also supply water to other factories in our cluster. One pipe is sometimes used to carry effluent waste in the other directions. We confirm that siphon has been observed in the MTMD pipe as in attached sketch. In another pipe we have seen the flowmeter reading negative values. We suspect there is siphon in this case also.
Swing check valve will work. Due to the size of the pipes, we want to check if there is another less costly solution.

 

[LittleInch]

Bit of a basic diagram, but you might be able to get away with a simple vent on the elbow before you drop into the overflow bucket. Pressure at that point should be very low if you're close to the end point so a pipe extending say 0.5m vertically shouldn't overflow but will allow air in to drain the pipe and prevent syphon.

A better sketch with some dimensions, levels etc would be better.

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

 

[SA07]

Thks for your advice

 

[katmar]

I agree with LittleInch's proposal. Better and cheaper than a non-return valve. An alternative would be to just cut the pipe shorter so that it does not discharge under the liquid level in the receiver tank. Depending on the setup you have this may cause splashing, but if the pipe exit is not under the liquid level it cannot run back. Another option - I have never seen it done, but cutting a slot in the pipe from below the last elbow (but above the liquid level) down to the end of the pipe would also break the siphon while minimizing splashing.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[Latexman]

I may be reading too much into your sketch, but it seems a 10 mm weep hole in each pipe at an elevation halfway between the left, inlet side and the outlet weir would do the trick. As mentioned, a dimensional drawing would be better.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[SA07]

Thks Katmar & Latexman

 

[LittleInch]

So what are you planning to do?

Feedback is always useful and helps close the loop.

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

 

[Compositepro]

The question is unclear and so is the problem.

"We have noticed that siphon occurs sometimes in an empty pipe. Is there a method to prevent this ? Is there a small device which can be installed on each pipe which can prevent this?"

A siphon cannot occur in an empty pipe. And the use of the word siphon rather than back-flow is misleading. Siphon infers that forward flow continues after the pump is off, in which case, a vent or vacuum breaker is the solution.

If you want to keep the pipes full after the pump stops, then a vacuum breaker is not a solution. In this type of system you would generally want to keep the pipes full at all times to prevent water hammer, flow surges, and pump trips. The pipes dipping into an overflow weir points to the intent being to keep the pipes full. For this you need a check valve. A simple solution would be a float ball on the discharge of each pipe.

I can see that siphoning could conceivably be causing water from other pipes being siphoned back through the stopped pump. But, in that case, the pipe could not be empty.

 

[Dhurjati Sen]

Dear Randhir,

There is a thing called NRV.

Regards,

DHURJATI SEN

 

[SA07]

We will consider all possible solutions and their costs and choose the best one. I cannot say what we will do right now.
We will have to present the solution and cost to the management and then decide.

We do not need to keep the pipe full after a pump is stopped.

On 3 pipes there is a pump which pumps water while on the 4th one water flows by gravity.

We want to enquire if there is another solution less costly than the NRV.