Centrifugal Pump Fundamentals: Parts 1 & 2

Overview:

With the exception perhaps of motors and valves, the component with the highest population in a typical ship's engine room is the pump, which is required whenever liquid must be moved from a location where the liquid is at a lower pressure or elevation to one at which the same liquid is at a higher pressure or elevation. The majority of the pumps used today are of the centrifugal type, and their design and operation is critical to successful shipboard operation.
The video below shares the 2.5-hour Part 1 webinar on the key design and operational fundamentals associated with centrifugal pumps.

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Follow up Q&A

Q: From Part 2 Chat: "Do you see movement away from split mechanical seals toward seals that outlast their equipment?"

A: Most pumps are expected to last for 20 years or more with periodic overhauls, including the replacement of wearing parts, and proper operation.
For example API610, Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries, requires that pumps be designed and constructed for a minimum service life of 20 years (excluding normal wear parts, such as bearings, seals, sleeves, etc.). In addition, these pumps should be designed for at least 3 years of uninterrupted continuous service.
Other specifications may require longer lives, such as some military specifications that require each pump to have a service life of 30 years with operation during 40% of this period.
In addition, in some critical applications, pumps can be expected to have a service life of 40 years with proper operation and maintenance.
Each main feed pump on a steam-propelled LNG carrier is typically overhauled every 5 years after approximately 2.5 yrs of operation (i.e., operating 50% of the time). During the overhaul, mechanical seals are usually replaced (regardless of their condition). Bearings and wearing rings are also replaced.
One issue that limits mechanical-seal life is the life of the elastomers that are used. One seal manufacturer states that O-ring life is approximately 10 years, which can include up to 5 years in proper storage prior to installation. Based on this, the expected operating life could be 5 years.
However, seal life can also be shortened due to various factors, such as dry running, inadequate or high-temperature flushing liquid, excessive vibration, misalignment, corrosion (sometimes when the pumped liquid is changed), excessive seal-chamber pressure, improper installation, and contaminants in the pumped fluid. In addition, seals that operate in lower-speed applications with lower-temperature clean liquids will probably last longer than seals operating with more severe conditions.
Taking the above into consideration, the average expected mechanical-seal life, provided that the seal is not damaged during installation and it is not abused during operation, is probably approximately 3 to 5 years. Also, API682, Pumps-Shaft Sealing Systems for Centrifugal and Rotary Pumps, specifies that all seals should operate continuously for 25,000 h (approximately 3 years) without the need for replacement. Therefore, mechanical seals would usually have to be replaced several times during the life of the typical pump.
Regarding split seals, they do have speed and pressure limitations. In addition, some of these split seals are designed to fit into stuffing boxes that originally were fitted with packing. Also, one seal manufacturer advises that their split seals may drip over a 24-hour period after the initial startup, so they typically should not be used with fluids that have emission limits.