WHY VENTS AND DRAINS REQUIRED 2

[stuarte]

Please can someone explain to me in laymans terms in general when would you implement the use of drains and vents on a piping system.I am told at all high points for vents and all low point for drains.But why? please help

 

[01101998]

you need to test the integrity of the piping system by hydrotesting it . To fill the lines you need to remove all the air from the system to avoid air pockets.That's why high point vents are requird. After hydrotest you have to empty thr line.That's why low point drains.

 

[MortenA]

Drain and vent could also be required during normal operation for almost the same reason e.g. if you need to modify the piping.

Best Regards

Morten

 

[zdas04]

For explosive products, you need vents to purge the lines after maintenance. For condensing products you need drains to remove condensation. Some thought into location of these fittings can save your pipeline operators untold effort over the life of a line.

 

[dbrechko]

Pneumatic testing is an alternative to hydrotesting. Although more dangeraous due to the compressible nature of air, it does not require high point vents or low point drains.

 

[KenRad]

In order to completely fill OR completely drain a piping system, both high point vents and low point drains are needed. Over the life of any piping system, there will be a need at some point to drain the system to replace a piping component, repair a leak, add a connection, etc. Completely draining a system requires manual vent valves at one or more high points, since the system fluid must be displaced by air in order to drain out. Without a sufficient path for air to enter the pipe, the system becomes air locked.

Low point drains are also useful for blowdown of accumulated sediment where needed.

The price of a few 3/4" weld-o-lets and ball valves is negligible in comparison with the benefit of having a system with adequate vent and drain connections.

 

[lago]

Almost everyone mentions the use of vents and drains as an aid to testing and blowing down the system, but you need to look at the process side also.
If you are designing a piping system for a compressed gas you will have to expect condensing of liquid from the gas stream as pressures / temperatures change. Low point drains, either automatic or manual, can get rid of this liquid load and reduce carryover.
As for high point vents, any liquid system that is filled and emptied on a regular basis has a need for venting to displace the air in the system as the liquid enters.

 

[owlscreech]

Anytime you intend to operate a system that pumps a liquid such as water in a power plant you must have a water solid system or you will end up with waterhammers and pump air binding (as well as other problems). Therefore after ensuring the piping lineup is correct, you "fill and vent," i.e., you fill the system witht the operating fluid while concurrently venting the system at the high points.

Obviously when you want to shut a system down for repairs that require opening the system, you need to drain the low points. This is almost always done with the vents open to faciliate (or even allow) draining.

Another reason for a solid system is mentioned above, i.e., to ensure that the hydro test is, in fact, just a hydro test and not a pneumatic test which as mentioned above can be very dangerous due to the explosive effect of air when released rapidly when the test fails.

Yet another reason for a solid system is for proper system lay-up, that is to put it in standby when not needed. Removing all the air, i.e., the oxygen, is needed to ensure corrosion is minimized. Sometimes O2 scavengers are used, e.g., hydrazine, to facillitate the process.

 

[11echo]

AS everyone has indicated, normally hi point vents and drains are either used for hydro testing the system prior to start up ...OR they are use as a requirement for the process or function of the piping system. And on rare occasions they can be used for both testing and operation.
It has been my experience that we let the contractors locate and install vents/drain as required for hydro testing. They can determine where they would like to see and readily use these connections. Then after testing, these connections are normally "seal welded" shut, with the exception of vents and drains needed for system operation. My 2 cents. Good Luck! ...Mark

 

[uthaya]

Hi stuarte,

The purpose of giving drain in lower points is to take out the drain where all liquid matter will be deposited. This will lead to disturb your flow rate and affect your system
efficiency.

The same way, the purpose of giving vent in upper points in pipeline is to takeout all gases( including vapour, air)
which will try to stay in the top of the pipe. This also will create so many problems like corrosion in pipes, non-
uniform flow.

The above said reasons are the purposes to give drain & vent in the pipelines.

I hope this will be a answer for you.

thanks,
uthaya.

 

[MortenA]

uthaya

I dont think it very common to use low point drain for your purpose. That would require something like a steam trap and a return line - not the way a low point drain usually is hokked up.

If you expect large quantities of condensate your piping should be designed with a slop towards a KO drum - no low-points!

Best Regards

Morten