Page 213 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

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INBOARD SEAL OUTBOARD SEAL

Ficlure 13-19

The ge neral tendency with double seals is to think that one seal in a dual
,-ant rnstlrl f-il -nA tha nthar wm~lrl L;rL-;n c nv h-oL r~n Thir ;c sr,ht,
arrangc,llc,lL cuulu nasi aivu lllc VIllcl IvuuIu c~-tt# a> a >roic VI UCILI\ ur. ir143 L> vriry
cars have a spa re tire, why a passenger jet h as a pilot and a co-pilot and why our
bodies have twc kidneys and two eyes. One co uld become incapacitated, damaged or
fail and the other wow assume rne runctio ns. This is the case with other double
IL_ z
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seals but not th lis one in the applications whc !re it is most specified. As soon as one
fails the other \n /ill follow.
The tandem dual seal is mostly mated to a pressurized barrier tank, or a
pumping unit as the support system. Support systems are discussed later
in this chapter.

The back-to-back double seal

This type of double seal (with back to back faces) is pressurized above
the pressure inside the seal chamber (Figure 13-20). It is recommen-
ded for toxic, explosive, costly, dangerous, and volatile liquids. It is
important to maintain the seal pressure above the pumped pressure
inside the seal chamber.
To obtain the benefits of this seal, it is necessary to install a gauge
indicating the actual seal chamber pressure. Sensors and transmitters
can be used to monitor and act on a pressure change. One of the two
seals can fail without product loss or fugitive emissions. This seal would
be connected to a pumping unit seen later in this chapter.

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