Metal Bellows Mechanical Seals Design Features
1. Wide service range from cryogenics to heat transfer liquids and corrosive chemicals.
2. Long service life—only one moving part.
3. Flexible bellows construction eliminates seal hang-up due to solids or dirt in pumpage.
4. Metal sealing wedge eliminates temperature restrictions of elastomers or plastics.
5. Built-in hydraulic balance eliminates step in shaft or sleeve*.
6. Available for either inside or outside mounting.
7. Stabilizer tabs prevent possible damage to the metal bellows due to vibration and excessive shaft run-out.
Nested Ripple design with advanced welding techniques insures maximum bellows strength and fatigue resistance. It all but eliminates stick-slip failures.
Hastelloy "C" is used in both the MB and the MBFG bellows. It is far superior to 316SS, AM350, and Alloy 20 in corrosion resistance, stress corrosion cracking resistance, and yield strength. Alloy 20 has a yield strength of 35,000 psi while Hastelloy C has a yield strength of 58,000 psi, a 66% increase! That is where it counts; in the bellows.
Drive set screws are Hastelloy "C" on both the MB and MBFG Hastelloy "C" set screws reduces galling problems that result with 316SS set screws. The 66% greater yield strength also insures that your Allen wrench will not "strip out".
Metal bellows mechanical seals will not fret the shaft or sleeve because it has no dynamic (sliding) "0" ring. All pusher seals (seals with springs) have dynamic "0" rings. This means that you can mount either metals bellows seal directly on the shaft and save the cost of a sleeve.
Because the bellows spring does hot have to overcome "0" ring friction drag, as does the pusher seal, the spring load can be lighter in the MB (Metal Bellows) and MBFG (Metal Bellows - Flexible Graphite) mechanical seals bellows then in the pusher seal design. Some common pusher seals have spring loads of 35 to 45 psi, while the metal bellows load is approximately 25 psi. This can result in up to a 50% decreased seal face wear rate. The Metal bellows produces even face loading, superior face tracking and less frictional heat.
*Built-in Hydraulic Balance: balance diameter lies within the bellows itself. This provides the ability to handle pressures to 300 PSI (21.1 KG/CM2) and, in certain environments, up to 500 PSI (35 KG/CM2) without the time and cost of cutting a step in the shaft or sleeve.
Metal bellows mechanical seals are also made into single and double cartridge configurations.
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