Seepex BN 5-12 Series, Operation & Maintenance Manual

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Operating Instruction for Double-Acting
Mechanical Seals / Back-to-Back Arrangement Dokument / document
ZU.016.02e
Ausgabe / issue
A / 18.06.98
Blatt / sheet
1 (2)
1.
General
Double-acting mechanical seals or mechanical seals in back-to-back arrangement are used when
conveying liquids that have typically the following characteristics:
−
aggressive, toxic
−
sticky, highly viscous
−
polymerizing
−
tendency to sedimentation
−
high steam pressure or gaseous
−
high pressure, high temperature
liquid atmosphere
double-acting back-to-back
2.
Flushing liquid
To function, double-acting mechanical seals require a flushing liquid which carries off the frictional
heat and prevents the product penetrating the sealing gap. The flushing liquid fills the space between
the product sided and atmosphere sided mechanical seals of a double-acting unit.
The flushing liquid pressure must always exceed the max. product pressure by min. 1.5 - 2 bar
so that product penetration into the sealing gap of the mechanical seal is prevented.
In principle, a clean, cold and stable fluid is used as flushing liquid.
Most simply, water from a vessell or a flushing pressure system can be used
(refer to point 3.1 and point 3.2). Flushing liquid must be compatible with the pumped product and be
free from solids. It must not tend to sedimentation and should have low viscosity and good thermal
conductivity. Additionally, the resistance to corrosion of all contacted parts has to be noted.
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