What will be the preferential location for tap-off to the main header for water line in pipe rack(upside or downside)..?

Water piping should exit the rack with a vertical down-and-under to avoid a high-point air pocket collection point.

Steam piping should exit the rack with a vertical up-and over to avoid condensate collection points.

Regardless of flow.

Anton,
W.r.t your answer, one more question arises, Why it is said that utility lines should be tapped above in header? And it is applicable to all utilities (Plant Air, Utility Water, Nitrogen, Steam, Potable or Drinking Water)

Thank You
Siddharth Jain

Sidjain,

Anton is quite right with the answer which he provided. This has been the generally accepted criteria since time in memorial. Liquid may have a little gas; gas may have a little liquid.

There are two qualifications which may also be applied to the above rule and could perhaps suggest the origin of your (very) particular design criteria. Very often design standards may require that utility lines are positioned on the top tier of the arterial piperacks. In such cases bottom tap-offs may lead to “ugly” layouts between two tiers. I realise that I could be taken to task in this forum for using such a non-engineering term, but sometimes aesthetics is the mark of healthy piping. If your utility consumers are positioned below the rack, from a flexibility perspective it is better to route the off take up-and-over, in a u-pattern to your consumers, as opposed to a down-across (and down), z-pattern form. The opposite is true for consumers above the header.

The second qualification relates to the possibility of solids formation / entrainment in either your air or liquid lines. If, for example in a potable water or fire water line, there is the possibility of algae formation, entrained sediment or scale in the lines or formation of ice within cold services or due to cold conditions, it is best to tap-off from above the header to reduce the carry-over of solids / semi solids and mitigate blockages. This of course does pre-suppose that no or insufficient filtration is present.

Therefore in summary, consider:

Liquid may have gas
Gas may have liquid
Caveat: Liquid or gas may have solid

2M

Thanks 2M,
It clarified things

Siddharth Jain

General rule.....
Liquid take-off from the bottom to allow draining so no low points that could freeze or plug.
Vapour take off to the top to avoid high point vapour collection which could result in the vapour condensing into a liquid.

..... and remember, these are "general" rules!

There will always be exceptions, and an exception is what makes a rule.

You may have to conect to a header with a sloping line, with no pockets allowed in the system, you may come across situations where you might encounter physical restraints to coming off top/bottom, if your header is in a trench you might find it difficult to come off the bottom etc, etc.

General rules are generally there to be followed generally, and that is why every connection must be considered on its own merits, you should decide if there is a requirement to deviate from the rule.

Very simple rule to logical understanding-------
Liquid take-off from the bottom to allow draining so no low points that could freeze or plug.
Vapor take off to the top to avoid high point vapor collection which could result in the vapor condensing into a liquid.

Of course there are constraints & we have to go for the deviation to the above logic but normally ......above logic is good enough.