Mechanical seal is a sealing fitted on the shaft of the centrifugal pump to prevent fluid leakage from the pump impeller. Mechanical seal act as a check valve and a slider bearing. The obvious function of check valve is to prevent liquid under pressure from leakage out of the pump or from drawing air into the pump ,when under a vaccum condition.
--Mechanical seal is pressed up in the top of the impeller vane and fitted to the pump shaft by circlip.
--It has many part Rotary seal and stationary seal. The rotary seal has a spring.
--The rotary part of a seal has a ceramic porcelain or carbide material.
-stationary part seal are made of highly finished carbon and rest on mechanical seal cover while is bolted to pump casing and this seal does not rotate. The stationary seal ring are brittle and can be easily chipped or damaged so it should be handled with care.
- Spring in the rotary. seal is there to compensate for microwear down of the rotary part carbon surface and rotary part carbon material.
- The o-ring is there in both stationary and rotary seal and are made up of rubber like substances called an elostomers. This type of elostomers material is selected to match the temperature limit and types of material being pumped. Should the temperature limits exceeds o-ring becomes hard and cracks sometimes.
MECHANICAL SEAL INSTALLATION
1) check the rotary full length and marking note down.
2)Mark where to put stationary and rotary to shaft and fit it.
MECHANICAL SEAL LEAKAGE
1)Incorrect type of mechanical seal
2)Bent shaft
3) mechanical seal improperly installed
4) O-ring damaged
5)mechanical seal runs dry can cause the faces to become hot without lubrication and the carbon faces can turn to a dull black powder.
DAMAGE TO MECHANICAL SEAL
1) due to abrasive particle in the liquid being pump(ex.mud in sea water) infiltrates with the liquid between the seal faces and grind away the carbon priming rings.
2) heat damage- excessive heat can damage primary ring and the elastomer parts.
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