Mechanical seals are key components in centrifugal pumps that prevent fluid from leaking out of the pump casing. They consist of two faces, one stationary and one rotating, located between the impeller and rear casing. Pumps in harsh environments require more abrasion-resistant seals than regular pumps. Mechanical seals reduce leakage compared to gland packings, saving power. Proper flushing plans are needed to lubricate, cool, and clean the seal while removing particles to minimize abrasion and extend seal life. Common operational and maintenance errors that reduce seal life include dry running, suction choking, foreign materials, improper flushing plans, misalignment, stuffing box issues, and failed bearings.

1. Mechanical SealBy Mr. Om Pratap Singh

2. Parts of centrifugal pump

3. Why sealing required !Key component of the pump is its mechanical seal. This spring loaded component consists of two faces, one stationary and another rotating, and is located on the Pump shaft between the impeller and the rear casing (see figure below). It is designed to prevent fluid from seeping outside of pump casing towards motor. Pumps designed for work in harsh environments require a seal that is more abrasion resistant than pumps designed for regular use.

5. Mechanical Seal Vs Gland PackingsLoss of Material A basic comparison with the leakage rate for the compression packings and mechanical seal yields the followings: (25 drop/minx60x24)+45 drops/day=800 a leakage ratio of packings to seals of 800:1Power saving: 50% Less power consumption in Mechanical seal.

6. Cross-sectional view of mechanical seal

8. Gland packing

9. How Mechanical Seal Works !

11. Secondary Sealing Elements

12. Need of API Flushing PlanTo lubricate and cool the pumps mechanical seal.To remove foreign particles to minimize abrasion.To remove carbon deposition on compression unit.To dilute ingresses material between Seal faces.It could provide safety to the seal from dry running to the some extent.To maintain the operational parameters of mechanical seal for which it is designed.

13. PLANT 11Plan 11. A line is connected from the discharge side of the pump and recirculated through an orifice into the gland flush connection. Orifices are hard to size and since many pumping fluids contain solids orifices are easy to clog

14. PLAN 62The quench gland. Often called the API gland

15. To cool the product we are sealing

16. To dilute any leakage that might migrate across the seal faces.

17. To introduce low-pressure steam behind the seal to put out a fire.

18. The Quench connection is labeled (Q). A close fitting bushing (DB) in the end of the gland directs the quench fluid down a drain hole on the opposite side of the seal gland

19. Steam is the most popular quench medium, but care should be taken that the steam pressure is very low, or the hot steam will penetrate through the nearby bearing seals and contaminate the bearing oil. API PLAN 32

20. API PLAN 13

21. Operational and Maintenance ErrorsOperation error is the single most cause in seal failure in throughout industry today. Some are mentioned below :Dry running.Suction chocking.Foreign material.Material Incompatibility.Abnormal process parameters.Flushing Plan Off.Maintenance fitting errors are also affects the mechanical seal Life :Misalignment < 0.02 mmStuffing Box Concentricity or gland register <0.1 MMShaft Run Out < 0.07 MMStuffing Box To shaft Perpendicularity < 0.07 MMEnd Play (Hold b/w 0.02 MM – 0.1 MM)Radial Deflection < 0.07 MM Failed BearingsUnavailability of Flushing Plan Required

22. Stuffing Box Concentricity or gland register <0.1 MM

23. Stuffing Box To shaft Perpendicularity < 0.07 MM