Do end-users really care about fugitive emission, or do they only want cheaper valves? Part 4

Do end-users really care about fugitive emission, or do they only want cheaper valves? Part 4

 

In the first part of this article I asked the following question: Is the situation different to day, then back in the 90´s? The answer was: Yes and No. One of the things I did not mention, witch is the best thing happened are the: Certified low-leaking valves packing technology in accordance with the EPA (United States Environmental Protection Agency), tested in accordance with API 622, witch has a maximum allowable leak-rate of 100 ppm. Yes, the situation is improving! When the Certified low-leaking valve packing technology require a written guarantee that the valve packing technology will not leak above 100 ppm for five years. This is a step in the right direction. Yes, the packing technologi has improved tremendously the last two decades. The packing itself will not leak for the next 5 years. But, what about the valve? What about the were and tear of the packing material from the operation of the valve, with a coarse spindle surface. What about bad tolerances on the valve parts? The API 622 specifies a test stand witch will use a 1/4 “ (6.3 mm) packing, the test stand itself are equipped with a spindle 25.4 mm +0.0/-0.2 mm with a surface finish of 0.40 – 0.80 mm Ra. The packing groove ID is specified to 38.1 mm +0.25/-00 with a surface finish 3.20 mm Ra + 1.25/-0.625 mm. The groove ID 38.1 – stem OD 25.4 : 2 = 6.35 mm cross-section on the groove. This is in compliance with fig. 12 recommendations from one packing manufacturer. The packing technology is fine. But if there are no specifications and demands regarding the valve packing box dimensions and tolerances within all sizes and pressure rates, the valve manufacturer are free to produce cheep valves with bad tolerances and it will be up to the end-user to control all the dimensions when repacking a valve.

 

Fig. 15

Fig. 15

Fig. 15 indicates 6 measures on the stuffing box, where the most important measures are 1) depth of the bonnet groove 2) ID in the bonnet groove 3) OD on the spindle and 6) compression height of the packing compression ring. Measures 4 and 5 are important too, with regards to the packing extrusion illustrated in fig. 13 and 14.

To be able to get the benefit from the Certified low-leaking valve packing technology, you must treat the packings right. You have to role the low density lace to fit the measures of the packing groove within 0.1 mm. You have to cut the packing lace in 450 angles, at the right length, with a packing cutter, illustrated in fig. 16. You have to install the packings with the cut angel as illustrated in fig. 17, then the split will be close. You should install the packing split with 1200 between them. The personnel working with the valves needs to be trained in how to repack valves. It does not help with excellent packing material, if it is used in the wrong manner due to lack of competence.

 

Fig. 16

Fig. 16

Fig. 17

Fig. 17

 

 

 

 

 

If you are using die formed high density Grafoil rings, the packings itself can still be within the Certified low-leaking valve packing technology requirement. The packing itself is OK, now it boils down to the dimensions indicated in fig. 15. And the tolerances on the parts indicated in fig 12.

 

If the next goal could be standardisation of the construction itself, making the six measure illustrated in fig. 15 identical within the same dimensions and pressure range. If the measures and tolerances were right, you could choose between Chevron rings, die formed or braided packings in the same valve. To day that is not a possibility. You could not replace graphite packings, with a stack of Chevron rings into a wedge gate or a globe valve. The surface finish and packing groove dimensions is not within the tolerances needed by Chevron rings.

 

If the dimensions and tolerances were as requested in this article, you could use less force when compressing comprisable packings. By using less compression, the result would be less friction and less wear with an expanded lifetime.

 

What is in the end-users interest? Answer: Better valves, safer valves, valves with less fugitive emission, valves within Certified low-leaking valve technology. I think, the end user really do care about fugitive emission, but some of them want cheaper valves too. Better valves with standardized stuffing box parts will unfortunately lead to some increased price on the valves. But with better valves (not only better packings), we all will become the winner.

THE END

 


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