Vent At Higher Point In Piping

Without a vent at the top, how do you ensure that the piping is completely full of the hydro test fluid?

Maybe this is an attempt to kill two birds with one stone; i.e., pneumatic and hydrostatic tests thrown together as one. ξ

And, wouldn't that be a pretty good test? Can air leak out easier than water?

These tests are looking for somewhat different things, and are not really interchangeable.

Good design should always include high point vents, to eliminate any air in the system, remember that air is compressible and if system is under high pressure liquid you could have a serious issue of air building up during the initial filling of the system.

High point vent is to open during filling, when liquid is present you know the system is full and the air is eliminated, but besure it is truly the high point.

Air in the system can cause havoc with instruments, pumps and many other devices.

Get the air out !!!!!!!!!!!!

And note that there may be more than one high point. Piping configuration may dictate several local high points

While all of the previously mentioned "values" of one or more high-point vents are valid- the results of the hydrostatic test is/was not compromised by potential air presence.

Any air would have been compressed to the same pressure as the fluid in the test. Any leak would have caused a loss of pressure. IF you saw no pressure drop- absolutely NONE- then you have a "tight" piping system.

If you saw ANY pressure drop- whether you saw water or not- then your pipes are not sound.

Net effect- Yes, air vents are useful (only if they are capable of holding the test pressure) AND- if they are automatic, you must run a drain pipe from them to a "safe" place because they will ultimately fail and start dumping water. BUT- they are not needed to do a valid hydrostatic test so long as the observation time is adequate and the gauges used are precise enough to verify that there is NO pressure drop.

Air being compressible, it will take more time to raise the pressure. Also, during pressurization, air may find its way through gaskets. Vent is essential to avoid it.

Please specify application whether this is recirculation of water(like HVAC system) or supply to building onlywith open outlet(like house plumbing)

your missing the whole thing, house plumbing is normally a closed loop system, air in any liquid system is a problem. If you have done any design/build in industrial or commerical systems you would have not asked such a question.

Hydrostatic test is basically a strength test for piping and if it is already conducted successfully as per the provisions of code B31.3, may be with little air pockets, I think retest may not be required. Sometimes retest may be damaging, particularly for gas pipes by enhancing rate of corrosion. Also you may loose water, power and efforts in addition to delay in project without any appreciable gain.

I can"t believe all the misguided information being stated, If your client wants an high point vent put it in. First mistake was not ensuring all the air is out of a liquid system, when hydo testing lets say you are looking for leaks in the system, how do you find an air leak in any major piping system? you cannot see it but only look at the system pressure dropping, and where do you start looking?

Water will leak and you will be able to see it very easy and find all the leaks specially in a threaded pipe system vs welded.

As I stated before air in a liquid system will only cause problems with instruments, get the air out so you can be certain that when hydro testing you have no high point air pockets that may leak but cant find the leak . case in point, would you like to fill the system with a very strong caustic or acid and then find a leak.

in closing if you do not understand why high point vents are needed why are you involved with the installation and testing?????????? it sound like your unqualified.

Dear Mr.Shavessels,

The Client is RIGHT.

For any Hydro Static Test, AIR VENT is a MUST, and NO AIR should be allowed to remain inside the Pressure parts to be tested. This is possible only when AIR IS VENTED OUT from the top most point.

If 3 crests are there in the vessel to be tested, the vent also should be 3. In other words, each CREST should have one vent and water should flow out which confirms Air is removed from the vessel to be tested.

If by chance air is remaining inside, it will also under go COMPRESSION which will take more time to reach the Test Pressure. Generally Water is used for Hydro Static Testing which is IN-COMPRESSIBLE, and the VOLUME Reduction is very small, during compression. Air is is HIGHLY COMPRESSIBLE to such an extent of 1/85 of its original volume at Atmospheric Pressure and Temp.

DHAYANANDHAN.S