Mechanical Seals vs Gland Packings

The argument for Mechanical seals vs Packing glands has been lenghty since asbestos related packing glands fell out of favour in the mid 90's. Since then both have experienced favour in the industry but in reality they both have a place and time to be used. We have tried to sum this up into an easy to interpret table below.
 

Comparison Packing Mechanical Seal
Initial Cost One Unit Cost 10 Unit Costs
Reliability Ample warning of impending faulure with good possibilities of correction Little or no warning of end of working life with the possibility of sudden failure
Installation Very simple, little skill needed. Correct procedure to be followed by manufacturer Skilled fitting and controlled environment needed for precise alignment
Running Maintenance Extended service life is achieved by adjusting gland at maintenance intervals None between seal refurbishment
Spares Cut to lenght. Relatively low cost and readily available Specific seal components can be tricky to get. Cost of holding stock can be substantial
Shaft Wear Can be signifcant in highly abrasive slurries None between seal refurbishment
Operating Costs Friction losses sllightly higher with packing. Slight media leakeage needed for fluid film lubrication Usually very low leakage of fluid media. Clean fluid is often needed at the seal faces for satisifactory performance
Absorb Eccentric Forces Yes No
Typical Operational Paramaters Up to 25 Bar 25m/s Up to 35 Bar 25m/s
Temperature Range Typically More Limited to spring & seal

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