High Points Vents and Low Point Drains

[indimech]

All,
Let me start my quest with this subject.
My question is does the location of high point vent depends on flow direction? And does the number of H P vents depends on the length of piping?
To be more precise, attached file is part of routing for Amine Oxide. Which is suitable location for a high point vent in the piping point A or Point B to place a H P vent after the first riser starting from right side.

And Is one H P vent sufficient in horizontal run of 40' near point B or in point C segment?
Does it require more H P vents or L P drains?

Thanks
Disciple

 

[racookpe1978]

Consider that vents are almost always used under startup and after shutdown conditions of very low flow => rarely - though not "never" - at high flow conditions when flow direction matters.

Drains frequently require flow backwards down pipes after the pump/pressure vessel/pressure is "off" => again, which sometimes causes problems when check valves actually really work and prevent the fluid from actually draining out.

 

[0123654789]

the vents and drains are correct on your routing. we don't need more.

 

[indimech]

thanks for the contribution

My context of refering to flow direction is like when the flow is from left side of pipe in attached iso, the air inside the pipe will be pushed and displaced by the fluid. If the vent is just after the top elbow of riser there will be less possibility that the air will be released from the vent completely most of the air will go further. If we keep the elbow at the end of horizontal run after the riser it may allow more air to escape. This is my thought process only.

Again I have doubt whether keeping the vent at the end of horizontal run will make any difference because the air can travel after that point in the pipe as it travels from the top of riser position.

I would appreciate if somebody can elaborate the concept of positioning the high point vent.

Thanks

 

[vpl]

indimech

Most of the cases I've seen have the vent right at the top where the pipe changes from vertical to horizontal.

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[0123654789]

air will be released completely as long as the vent is on the highest point.
fluid level raises evenly on horizontal part, air will be pushed to the highest point.

 

[pennpiper]

indimech,

The location of the vent (or Drain) is important and should be given careful consideration BUT not for the reason that you stated. It has nothing to do with flow direction.

The criteria for the location of High Point (Hydro-test) vents and low point (Hydro-test) drains is access.

The Installation contractor is normally responsible for doing the Hydro-test and need to get to the vent or drain. They do not think very kindly of piping designers that put vents (or drains) in locations that are not accessible.

 

[indimech]

@ vpl
I have also seen most of the vents just after the riser. But I don't know it is just a practice followed in piping or is there any logical technical reason.

@ 0123
Your reply leads me to think whether the fluid fills a pipe level by level like a tank or it fills like displacing the air, like a pig pushing the product, and filling the pipe completely in a cylindrical manner.
If flow velocity is less it would fill level by level but at high velocity also will it fill level by level?

@ pennpiper
Do you mean that as long as the vent is on highest point, assuming that highest point is on a horizontal section of pipe, position of vent doesn't matter whether it is start of horizontal run or end or in between if it is accessible to the personnel?

Doesn't a high point vent have any other use apart from pressure testing ? Say during start of another batch ?

 

[0123654789]

indimech,

High point vent is used for hydro-test and start-up.

In hydro-test, fluid level would fill level by level.

In start-up, I only know for steam line, steam will mix some air acting as a piston. Air would not be vented completely even putting a vent at the end of horizontal run after the riser. Normally a vent is placed at the remote end of each line.

So, pennpiper is right, we only consider accesibility for the location of high point vent.

 

[indimech]

If we consider a process which goes through 4 batches per day and CIP cycle after each batch then during start of every batch doesn't the conditions are same as startup or hydrotest.
If we don't use vents during start of each batch why do we need to use vent in hydro test?

Sorry for asking too much but whenever I start thinking lot of questions come to my mind..Please bear with me.

And thanks for replying.