Jump to content



Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

3-Stage Propane Ref Performance

3

High Point Vent Size

vent size vent requirement

9 replies to this topic
Share this topic:
| More

#1 Sherif Morsi

Sherif Morsi

    Gold Member

  • Members
  • 159 posts

Posted 29 July 2017 - 01:15 PM

Hi,

 

We have a 2" open drain line that will be used to drain a main seawater header. I believe this will require a high point vent connection in order to allow draining of the main header (this drain line will be used after the header is disconnected from the system and depressurized).

 

What are the criteria for sizing this vent connection? Any resources I can look at?

 

Thanks

Sherif



#2 Bobby Strain

Bobby Strain

    Gold Member

  • Members
  • 2,226 posts

Posted 29 July 2017 - 03:12 PM

You can perform a calculation using various vent sizes. Should be quite quick to do. Drain time and minimum header pressure with an open system.

 

Bobby



#3 Napo

Napo

    Gold Member

  • Members
  • 290 posts

Posted 31 July 2017 - 08:53 AM

Sherif,

 

You can use the following "rule of thumb":

 

Vent diameter = pipe diameter/4

 

I attached related information.

 

Napo.

Attached Files



#4 Sherif Morsi

Sherif Morsi

    Gold Member

  • Members
  • 159 posts

Posted 01 August 2017 - 02:18 PM

You can perform a calculation using various vent sizes. Should be quite quick to do. Drain time and minimum header pressure with an open system.

 

Bobby

 

Sizing the drain header and determining the drain time is not a problem.

 

I meant, for example if I have a 1.5" drain time and it would take an hour to drain the main header, what would be the proper vent size required to achieve this? 3/4" or 1" or 1.5"? Where can I find a procedure to determine this size?

 

Thanks Napo, Have a question, the procedure on page 6 is for Vacuum relief not just atmospheric vent (high point vent). Can I use it for high point vents? If yes,

- the flow is in cubic feet per second?

- what's the pressure limit?

- Do you know of a reference for this question?

 

 

Regards,

Sherif



#5 Napo

Napo

    Gold Member

  • Members
  • 290 posts

Posted 02 August 2017 - 06:09 PM

 Sherif,

 

The procedure on page 6 is for vacuum relief only.

 

Other recomenndation says: "Drains, vents, and simple connections shoud be 3/4 in. minimum." from the book Pipping Design for Process Plants of  H. Rase, edited by John Wiley And Sons, New York, 1963.

 

If your main head pipe is pressurized the first step is drain (this to do low pressure), after you can employ vent, this is for safety.

 

I havenĀ“t found a reference for to calcul exactly your question.

 

Napo.



#6 Bobby Strain

Bobby Strain

    Gold Member

  • Members
  • 2,226 posts

Posted 02 August 2017 - 10:16 PM

If I didn't know what to do then I would provide a 1 1/2 inch vent. Can't go wrong.

 

Bobby



#7 Alexsandres

Alexsandres

    Junior Member

  • Members
  • 27 posts

Posted 03 August 2017 - 11:58 AM

Hi,

 

We have a 2" open drain line that will be used to drain a main seawater header. I believe this will require a high point vent connection in order to allow draining of the main header (this drain line will be used after the header is disconnected from the system and depressurized).

 

What are the criteria for sizing this vent connection? Any resources I can look at?

 

Thanks

Sherif

 

Hi Sherif,

 

In one project which I was involved, free draining velocity criteria was considered as 0.9 m/s. For 2" drain valve, maximum allowable flowrate would be around 6.6 m3/hr.

 

If I were you, I'd check hydrostatic from header whether flowrate could go higher than 6.6 m3/hr or not. In case I could have higher flowrate, thus some limitation is required. Let say, additional globe valve (by certain opening) or consider smaller drain valve to limit maximum flowrate as 6.6 m3/hr only.

 

Related to vent line, my understanding is that this vent line would act like inbreathing (air would be sucked due to volumetric displacement of drained liquid). If vent line is too small, actual volume air entering seawater header would be slower than liquid draiing rate. This would cause vacuum on the seawater header.

 

So, vent line (or inbreathing line) should be designed by actual volumetric displacement of the liquid draining rate. An 3/4" vent valve should be okay in this case (for 6.6 m3/hr volume displacement).

 

Alex



#8 Sherif Morsi

Sherif Morsi

    Gold Member

  • Members
  • 159 posts

Posted 04 August 2017 - 11:35 AM

Hi All,

 

Thank you very much for your feedback, very informative. 

 

This vent connection is gonna be the high point vent. When the 4" header is off service (valve closed + pump is not running), there will be no pressure in the line. The header will be drained from the lowest point via a sloped line. That's when we need the open the vent connection to avoid vacuum in the header.

 

So given a 2" line with a flow of around 6.6 m3/hr, would I need a 3/4", 1" or 2"? I though about 3/4" actually given what I have seen around the facility.

 

Your thoughts?

 

Sherif



#9 Napo

Napo

    Gold Member

  • Members
  • 290 posts

Posted 07 August 2017 - 10:05 AM

Sherif,

 

What is the length of pipe header?

 

This moment we know the pipe header diameter (4")and drain diameter (2").

 

Napo.



#10 breizh

breizh

    Gold Member

  • ChE Plus Subscriber
  • 3,670 posts

Posted 08 August 2017 - 07:28 AM

Hi ,

Consider the resource attached.

Breizh

Attached Files






Similar Topics