Pressure Sources - Grundfos NKG series Montage- Und Betriebsanleitung

6.1.2 Back-to-back seal arrangement with cartridge seal
2
Fig. 4 Back-to-back 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 Pressure sources

The overpressure in the barrier fluid in the seal chamber in
relation to the pumped liquid pressure can be maintained by
various pressure sources:
• an existing pressure source (many applications incorporate
pressurised systems)
• a separate pressure source (e.g. a dosing pump unit)
• a pressure intensifier.
6.2.1 Existing pressure source
Standard shaft seals: The existing system may provide both the
barrier fluid and the overpressure. It can be either a dead-end or
a circulating solution. In both cases the barrier fluid pressure
must be fixed at a prescribed overpressure level,
see section 5.1.1.
Cartridge seal: The existing system may provide both the barrier
fluid and the overpressure. A cartridge seal is not for use with a
dead-end solution. The barrier fluid pressure must be fixed at a
prescribed overpressure level, see section 5.1.1.
6.2.2 Pump with dosing pump unit (dead-end solution)
Fig. 5 Pump with dosing pump unit
Standard shaft seals: The setpoint pressure of the barrier fluid
can be set by means of the pressure switch on the dosing pump.
When the pressure drops below the setpoint, the dosing pump
will start and thus maintain the overpressure in the seal chamber.
The dosing pump unit solution is mainly used in dead-end
applications where cooling of primary shaft seal is sufficient
without the cooling effect of recirculation.
One dosing pump unit can supply several pumps
Note
with back-to-back seal arrangements.
Maximum operating pressure in seal chamber: 16 bar.
Dosing unit outlet: 1 x Rp 1/4.
Note
Connecting pipes or hoses are not included.
Cartridge seal: A cartridge seal is not for use with a dead-end
connection.
A
1
6.2.3 Pump with pressure intensifier (dead-end solution)
Fig. 6 Pump with pressure intensifier
Standard shaft seals: The Grundfos pressure intensifier
maintains a pressure that is 1.5 - 4 bar higher than the pumped
liquid pressure, independent of the specific pumped liquid
pressure.
Relief valve
Seal chamber
Pump discharge
Fig. 7 Principle sketch of intensifier connections
The system maintains the overpressure automatically - from
standstill to max. operating pressure. The barrier fluid seeps
through the primary shaft seal and evaporates through the
secondary shaft seal. In this way the barrier fluid in the intensifier
is consumed over time, and the intensifier has to be refilled
manually.The barrier fluid inlet must be fitted with a non-return
valve to avoid back pressure to the source.
One intensifier can only supply one pump.
Note
The intensifier is mounted on the pump from
factory.
Maximum operating pressure of the pump discharge pressure at
the pressure intensifier: 25 bar.
Cartridge seal: A cartridge seal is not for use with a dead-end
connection.
Barrier fluid
inlet with
non-return
valve
7