Operating Conditions; Barrier Fluid; Installation; Barrier Fluid Connection - Grundfos NKG series Montage- Und Betriebsanleitung

5. Operating conditions

The operating conditions stated in the installation and operating
instructions for NK, NKG pumps also apply for back-to-back shaft
seal pumps.

5.1 Barrier fluid

The barrier fluid must be clean.
The barrier fluid should be selected according to
Caution
the application and must not chemically attack
the materials of the pump and the shaft seal.
Examples:
Application Liquids mixed into the barrier fluid
Heat transfer / hot Monoethyleneglycol (without
applications additives)
Chemistry / industry Customer wish
As the barrier fluid has a higher pressure than the pumped liquid,
it serves as lubricating liquid for both primary and secondary seal
faces. The barrier fluid will seep through the primary shaft seal
and be mixed with the pumped liquid. Consequently, the barrier
fluid chosen must always be compatible with the pumped liquid.
Barrier fluid seeping through the secondary shaft seal
evaporates.
Warning
If the shaft seal is used in applications where
special safety precautions must be observed due
to hazardous liquids, the customer bears full
responsibility!
5.1.1 Prescribed overpressure of barrier fluid
The barrier fluid pressure must be minimum 1.5 bar or 10 %
above the pumped liquid pressure close to the seal.
5.1.2 Maximum barrier fluid pressure and temperature
Due to the shaft seal design, the pressure in the seal
chamber/cartridge seal must not exceed 25 bar. The maximum
permissible temperature of the barrier fluid depends on the
rubber material of the shaft seal.
Shaft seal rubber
EPDM
FFKM
FKM
FXM
HNBR
These values apply to water as barrier fluid. If other barrier fluids
are used, contact Grundfos for the max. permissible temperature
of the barrier fluid.
5.1.3 Barrier fluid evaporation point
The back-to-back seal arrangement can handle a pumped liquid
temperature up to 140 °C. In order to ensure proper liquid
lubrication in the the seal gap, it is very important that the
evaporation point of the barrier fluid is at least 10-15 °C higher
than the temperature of the pumped liquid.
6
Max. permissible
temperature of barrier fluid
[°C]
+120
+140
+80
+140
+90

6. Installation

6.1 Barrier fluid connection

6.1.1 Back-to-back seal arrangement with two separate shaft
seals in a seal chambe
1
2
Fig. 2 Back-to-back seal arrangement with two separate
shaft seals in a seal chamber
Pos. Description
A Vent screw for pumped liquid
1 Primary shaft seal pipe connection - 3/8"
Secondary shaft seal pipe connection with vent screw
2
for venting of seal chamber - 3/8"
3 Secondary shaft seal pipe connection - 3/8"
In this back-to-back shaft seal arrangement the seal chamber has
three connections. See fig. 2 and fig. 3. Pos. 1 leads to the
pumped liquid side of the shaft seal, and pos. 2 and 3 lead to the
seal chamber. All connections are close to the seal faces of the
shaft seal.
Connections
2
1 3
Fig. 3 Direction of barrier fluid
Dead-end solutions (See 6.2 Pressure sources)
Use only connection 1 or 3.
Connection 2 must be plugged.
Note: Automatic venting of the seal chamber must be considered
for the application. Connection 2 can be used for this.
Circulating solutions (See 6.2 Pressure sources)
Use two connections. We recommend to use connection 1 as
inlet and 2 as outlet. This will create a crossflow, have a cooling
effect on the shaft seals, and at the same time provide automatic
venting of the seal chamber. Connection 3 must be plugged.
A
3