Do end-users really care about fugitive emission, or do they only want cheaper valves? Part 2
Do end-users really care about fugitive emission, or do they only want cheaper valves? Part 2
The braided packings are to be cut to fit the packing groove, whereas the die-formed are produced as finished rings. The Graphite packings can be high density, hard rings that can be compressible within 10-12% of its thickness, or low density, soft rings that are compressible up to 40% of its thickness.
Fig. 7
Fig. 8
Fig. 9
To be able to seal, the packing rings must be into good contact with both the spindle-side and the bonnet-side of the packing, shown with blue arrows on fig. 7. Because graphite fibres are very coarse most of the compression of the packings will go down-wards and very little will go out-wards to the sides as illustrated in fig. 8. Because of this fact, it is important that the packing rings fits perfectly into the packing groove, before compression starts. The reason why Garlock 9000 packings was so successful in the 90´s was the fact that the packings expended outwards due to the construction illustrated in fig. 9, when relatively little force was applied down-words the packings expanded to fill the hole packing groove and gave a good contact between the packing and the spindle/bonnet. The rest of the commercial I will leave to others. I am not saying that the low density, angel shaped, die formed packings, are better than braided packing rings. You just have to use the low density reinforced braided packings the correct way.
First of all the packing has to fill the whole groove within the 1/10 of a millimetre, just like the 9000 packings. To be able to do that the braided packing have to be rolled by a rolling pin like the one on fig. 10a.
Fig. 10a
Fig. 10b
In fig. 10b there are three braided packings, in fact it’s the same one being rolled. The one in the middle is the original 7.9 millimetre cross-section, witch have been rolled down to 6.9 millimetre; shown by the upper packing. And the packing in the bottom is the one from the top tilted 90 degree. As you can see that one is somewhat wider, it is 8.9 millimetre. This shows that the pacing is not compresses, because the one millimetre with graphite is moved outwards. This is done with carefully rolling. You cannot do this with a hammer or in a vice, then the packing material will get compressed and destroyed. If you do this right, the low density braided packings will have the same advantage as the low density angled packings illustrated in fig. 9.
Fig. 11
Next question! How many layers of packing should there be in one stack? It all depends on who you ask. I have been talking to packing producers, not valve manufacturer. The idea is that there should be enough but not to many. Five times the cross-section of the groove is a good base. Then the packings will be evenly compressed against the spindle. If you are putting too many packings into the groove, as indicated in fig. 11 you will get a higher degree of compression and wear on the upper most packings and less compression down in the packing-stack, then the packing rings on the bottom will not function as intended. This goes for all compressed spindle packings. So what about die formed high density rings? We will look into that matter in the next issue of Valve World.
To be continued in next issue.
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