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Flow rate through the seal chamber should be approximately 1 l /min. The correct pressure is most impor-
tant. The purpose of the manual valve in the exit line is to create the necessary backpressure so that
proper stuffing box pressure can be maintained. It is important that the exit line be attached at the top of
the stuffing box so air is vented out.
Single mechanical seals:
Single mechanical seals are normally used when the pumped fluid is suitable to lubricate the mechanical
seal. When pumped fluid is suitable to lubricate the mechanical seal recirculation from pump discharge to
the flush tap on the gland through the standard by-pass line can be used. Internal recirculation from a high
pressure point is also available as an option. Single seals can also be used when contaminants are present
in the pumpage if a throttle bushing is supplied at the bottom of the stuffing box. The bushing acts to limit
product dilution.
When contaminants are present in the pumpage, an external source of clean seal water must be supplied.
Figure VIII shows the recommended "Controlled Pressure System" for a single mechanical seal with a
throttle bushing. Seal water enters the seal chamber, lubricates the seal faces, and exits under the throttle
bushing into the pump itself. Positive flow in the seal water line indicates adequate seal water pressure.
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