The function of Mechanical Seals is to retain liquid product inside equipment which in turn prevents product entering the motor and escaping to the atmosphere.
I like how you mention the pro's and cons of gland seals, and then don't mention any of the cons of mech seals. like they're super expensive, and then they do fail, and they will,they fail detrimentally, causing massive leaks and possibly completely destroying the shaft they're on. unlike gland seals, where they, drip, and as they wear, just drip more.
Diamonds can cut diamonds. Diamonds can cut sapphire. Sapphire can not cut diamonds. Sapphire can not cut sapphire. SAPPHIRE CAN NOT CUT SAPPHIRE! Are we missing something here because somebody found a phenomenon they do not like?
