Flushing System - Grundfos NKG Montage- Und Betriebsanleitung

Separate circulation/cooling of primary shaft seal
Use connection 1. A pipe can be fitted between the pump
discharge and connection 1. Alternatively, an external supply can
be fitted to connection 1.
Circulation or cooling of the primary seal is commonly used in the
following situations:
• to avoid accumulation of particles in the seal face area
• to increase the pressure in the seal face area resulting in a
higher evaporation point
• to vent the shaft seal area in order to avoid dry running
• to provide cooling of the shaft seal. (The friction between the
seal faces results in a temperature increase of 10-20 °C above
the pumped liquid temperature. In this case the pumped liquid
itself can provide cooling).
6.1.2 Tandem seal arrangement with cartridge seal
2
Fig. 4 Tandem seal arrangement with cartridge seal
Pos. Description
A Vent screw for pumped liquid
1 Cartridge seal inlet pipe connection -3/8"
2 Cartridge seal outlet pipe connections -3/8"

6.2 Flushing system

Typically, one of these methods of connecting the flushing fluid to
the pump is used:
• circulation from a reservoir, see section 6.2.1
• dead end connection from a reservoir, see section 6.2.2
• external flushing fluid system, see section 6.2.3.
Common for these flushing solutions is that the pressure in the
seal chamber is lower than the pressure of the pumped liquid
around the shaft seal.
The flushing fluid acts as lubrication and cooling for the
secondary seal and keeps a liquid phase for the primary seal in
the seal chamber.
6.2.1 Circulation from a reservoir
Standard shaft seals: The seal chamber is connected to a
reservoir by means of two pipes.
Both the primary and secondary shaft seal generates heat during
operation. This heat energy is transferred to the flushing fluid.
Due to natural circulation, the heated flushing fluid rises from the
seal chamber to the reservoir where it cools down. The cooled-
down flushing fluid returns to the seal chamber, lubricates and
cools the seal faces.
After a period of time the flushing fluid in the reservoir must be
replaced due to contamination from the pumped liquid.
6
A
1
Minimum
1 m
3/8" outlet
3/8" inlet
Fig. 5 Tandem seal arrangement with circulating flushing
fluid
Circulation to a reservoir can also be forced by a separate pump.
Cartridge seal: A cartridge seal is connected to a reservoir by
means of two pipes.
An internal pumping function in the shaft seal provides sufficient
circulation of the flushing fluid to cool and lubricate the seal.
The cartridge seal is self venting.
After a period of time the flushing fluid in the reservoir must be
replaced due to contamination from the pumped liquid.
6.2.2 Dead-end connection from a reservoir
Standard shaft seals: The seal chamber is connected to a
reservoir by means of a single pipe.
The flushing fluid lubricates the seal faces, but cools them less
than in the case of circulation. After a period of time the flushing
fluid in the reservoir must be replaced due to contamination from
the pumped liquid.
3/8" inlet
Fig. 6 Tandem seal arrangement with a dead-end flushing-
liquid supply
The flushing fluid enters the seal chamber via a pipe from an
elevated reservoir.
No heat is dissipated from the system.
Cartridge seal: A cartridge seal is not for use with a dead-end
connection.