6 replies to this topic

[GavinH]

Hi
I am new and have been following this other topic;


http://www.cheresour...ipeline-design/

and have been asked to submit a separate topic.

I have lost my mathematical ability (!!) and am struggling to follow the formula in the other topic. I have attached a sketch showing my particular problem and am attempting to derive the correct pipe size needed to achieve the flow rates required based on the worst case water levels. Does anyone have a simple formula or can provide guidance on what pipe size would be appropriate based on the use of HDPE or similar?
Thankyou very much
GH

Attached Files

•  Holden Wood Siphon Details.pdf   160.17KB   115 downloads

[breizh]

Let you consider the resource given in the previous post ( hydraulic formula -example 7) , it is very similar to your query .
hope this helps

Breizh

[TS1979]

Based on my calculation, you need an 18" HDPE piping. The fanning friction factor will be smaller than I used. For the conservation, 20" HDPE piping will work

Attached Files

•  Hydraulic Calculation 1.xls   18KB   114 downloads

[GavinH]

Breizh - sorry I am not sure which formula you refer to. I have tried to use a couple of the formulas in the other topic and got a pipe size of 300mm diameter. I think this did not allow for any losses though.

TS1979 - thanks for the spreadsheet. Although I cant follow the calcs within it but can only accept your calculation of 18" (450mm diameter). Perhaps this sounds reasonable based on my calculation of 300mm with no friction losses etc allowed.

However, I would assume the various formulas etc would give different results anyway?
Thanks

[katmar]

Gavin, the circumstances of this question are very strange. If you are a student then you need to go back to your notes and revise this material, or make an appointment with your lecturer/professor and explain your difficulties. If you are in an industrial environment it would be very strange for someone with so little experience or knowledge to be allocated this task. What resources do you have at your disposal? Do have a Perry, or a Crane 410 manual, or any other fluids text? Are there other engineers in your department?

Whatever the situation, the problem at hand is too complex to just "throw a formula at it". You need to spend some time with the books to develop an understanding friction and fitting losses. It is not going to help you at all if someone here does the calculation and presents you with an answer and you do not understand where it came from. If you just want an answer then you need to engage a consulting engineer locally.

If you are prepared to be a bit more open about your circumstances and what you are actually trying to accomplish you may get more help here.

[vinnay1999]

Hello 

 

We have a 21 metre high tank which has an  incoming pipeline connection that is connected on the roof top with a 1000 dia HDPE pipe and continues to go down into the tank for 20 m.The top of the pipe is @ 23 m height. We have two pumps @ 5500 m3/hr each that are supposed to send water into this tank . We get a flow of around 8000 m3/hr (with both pumps operating) . We expected that we would get a siphon with this arrangement and thereby helps the pump with the flow rate.However we find that while the pumps are started the water is falling freely into the tank creating an air pocket on the top.We have a vent connection at the top of the tank , but when it is being opened to vent off the air , we actually find vacuum that is withdrawing more air into the pipe. We tried to suck air with a vacuum pump but without much improvement. Is there a way to remove the air from this pipe. Now we think to throttle the pump discharge to generate more velocity at the top so that we can have full diameter flow. Am I thinking in the right direction. Please throw some light

[katmar]

Vinnay, you should not attach a new question to an existing thread - especially not an old one like this that has not been posted to in over a year.  Repost your information as a new thread and you will find you get much more interest.  In addition to the information you have already given you should show the calculation that caused you to believe you will get a siphon.  A sketch is always helpful as well.  The sketch should show the position of the vent (it is not clear whether the vent is on the inlet pipe or the tank) and also show the range of operating levels in the tank.