||Bellow Seal Valves
|Primary stem seal
|Secondary stem seal
||Not Possible since Metallic Bellows are designed to last several thousands cycles
||Occurs as soon as the ring wear out.
||Very common. Due to friction between stem occurs within a few cycle no matter which make valve or quality of gland packing
||Rings need to be changed frequently
||Packing needs to be replaced very often
||Zero Loss. As the isolation is by metallic bellows, leakage (in ppm) is not possible.
||Large in case of leaks
||Considerable amount through gland leakages. Normally large amount when leakage remains unattended.
||Very High for replacing rings
||Very high for replacing gland packing
|Maintanance Cost often
||High as rings need to be changed atleaset once in six months
||Very high, Gland packing needs to be replaced / repacked. The cost along with equipment down tme, man hours spent act is very high.
||VeryLow - in -months. Due to leakage through gland, certain parts erode, making the valve irreparable after some months.
||Can be used safely for almost any media
||Can be used for limited medi like steam, hot water
||Highly unsafe when the media is hazardous / poisonous
||Comparatively higher initially but lowest total cost of ownership
||High compared to the benefits
||Initially low but very high after some years if cost pf packing, down time, man-hours spent, number of valves replaced act. are taken in to account.