Page 200 - Know and Understand Centrifugal Pumps

Mechan ica I Sea Is

mounted faces to compensate some axial shaft movement. The
balanced mechanical seal was patented in 1933. The balance feature
raised the pressures that the seal could withstand, and reduced the heat
generated between the faces. Mechanical seals were used on the
propeller shafts of submarines during the Second World War.
Mechanical seals replaced packings on the water pumps of jeeps and
passenger cars, and on refrigeration compressors in the 1940s. Oil
refineries began specifying mechanical seals as standard equipment in
the early 1950s.
The development of the mechanical seal advanced in parallel with
elastomer technology. Mechanical seals using O-rings and other
elastomer forms, benefited with improved shelf-life, maximum and
minimum temperature limits, better chemical resistance, and higher
pressure ratings.
To this day, balanced mechanical seals using O-rings are the standard in
industry. Mechanical seals continue to evolve in sealing face technology,
computer design, finite element analysis, cartridge designs, split seals,
double or dual seals, and ciry gas seals.
Nowadays, there doesn’t really exist a liquid, condition, or pump
operating situation that cannot be sealed successfully with a mechanical
seal. With the help of mechanical seals, man has been able to explore
the extreme pressures of the ocean depths, and the extreme vacuum of
outer space.

We say this because there are stii II people in industty who consider the mechanical
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.. . . .
seal to be something new. They say they‘ll continue to use packing in their pumps
until mechanical seals are perfected. This is like saying they’ll continue to use candles
until the electr ic light bulb is perfected.

Mechanical seal manufacturers design their products to last 5 to 10
years. The majority of seals are designed for 40,000 hours of operating
life. There are 8,760 hours in a year. This is approximately 5 years,
running a pump at 24 hours per day, and 15 years for a pump running
at 8 hours per day.
It doesn’t matter who manufactures the seal, almost all seals have the
same component parts, because all parts have to perform the same
functions. The common parts in all seals are: the gland, the stationary
face, the rotary face, the secondary seals, the spring, and the fastener to
the shaft. Let’s look at how mechanical seals are designed (Figure 13-3,
next page).

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