Fugitive emission in valves.

Ta-Luft - Technical instruction on air quality directive item 5.2.6. VDI 2440, has set the creteria under which leakage rate the packing of valve (any type) can be accepted using helium as the medium for the test. Helium has been choosen as it is the best inert gas and excellent sensors are availabe to smell it. The creteria also includes the application temp. range.

The test can be performed only once on the prototype design of the packing in the presence of a TPI like TUV inspector. And they witness and issue the certificate which can be accepted by a purchaser as a base reference for a type of valve, particular size range and temp. range for that design of packing or a spectrum of different designs of packing.

Now coming to your question, by packing I mean the stem packing of any valve. This act Ta-Luft was enacted to reduce the fugitive emmision of the plant. Most of the valve packing are degraded after certain cylces of operation and the service starts leaking. The Ta-Luft mentioned above is for only valve packing and includes the no. of cycle of operation where mechanical arrangement during testing, strokes the valve stem from close to open position automatically with a counter.

There are other Ta-Luft laws which dictates many other different type of emmisions other than the valve packing.

Helium leak test specific to individual manufacturer's own standard, as such is not accepted in the current market. Widely  accepted are the Ta-Luft and the Shell's SPE 77/312 which calls for more stringent creteria as the individual manufacturer's testing procedure are not much reliable without any reference scale.

Just for your information, nowadays most of the well known manufacturer's have adapted the Ta-Luft as a default design and offer it, even if you don't call for it.

Though this law is applicable only for Germany, it has been informally adapted by most of the European and Asian country plant owners. In USA the equivalent law is Called as Clean Air act. The approach is different in the testing and creteria but the end result emmision is slightly less stringent than the Ta-Luft requirements. The more stringent to follow is the Shell SPE 77/312. BP in US has its own standard like the shell in line with Clean Air act.

VDI is like the Institution of Engineers of India of Germany, The association of German Engineers but very active and creactive group having strong lobby in the government even today, which is responsible in bringing the Ta-Luft law more than two decades back well before the Clean Air act.

With regards,
Kannan
Linde, Germany.

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Sandesh Mane wrote:
 
Just a query...
Where are the low emmission valve used and is it related only to stem packing or some other design criteria is also there.
 
Do all low emission valves shall be helium leak tested /TALUF certified....
 
what is difference between taluf cert valves and helium leak test ??...which one is more stringent.
 
regards,
Sandesh Mane