Comparison Between Bellow Seal & Traditional Valves

  Bellow Seal Valves Piston Valves Conventional Valves Primary stem seal Metallic Bellow Piston Ring Gland Packing Secondary stem seal Gland packing None None Stem Leakage 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 Packing Replacement Not applicable Rings need to be changed frequently Packing needs to be replaced very often Replacement Cost Not applicable Very High High Media Loss 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. Equipment Downtime Nil Very High for replacing rings Very high for replacing gland packing Maintanance Cost often Nil 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. Valve Life High-in years Low VeryLow - in -months. Due to leakage through gland, certain parts erode, making the valve irreparable after some months. Safety 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 Cost 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.