Maintenance; Pump; Mechanical Shaft Seals; Motor - Grundfos NB Original Installation And Operating Instructions

11. Maintenance

Warning
Before starting work on the pump, switch off the
supply voltage. It must be ensured that it cannot
be accidentally switched on.

11.1 Pump

The pump is maintenance-free.
If the pump is to be drained for a long period of inactivity, inject a
few drops of silicone oil on the shaft at the bearing bracket. This
will prevent the shaft seal faces from sticking.

11.2 Mechanical shaft seals

Mechanical shaft seals are maintenance-free, working almost
without any leakages. If any considerable and increasing
seepage occurs, the mechanical shaft seal should be checked
immediately. If the sliding surfaces are damaged, the entire shaft
seal should be replaced. Mechanical shaft seals should be
treated with the greatest care.

11.3 Motor

Check the motor at regular intervals. It is important to keep the
motor clean in order to ensure adequate ventilation. If the pump
is installed in a dusty environment, the pump must he cleaned
and checked regularly.

11.4 Lubrication

Motor bearings
Motors up to and including frame size 132 have maintenance-
free, greased-for-life bearings.
Motors of frame sizes larger than 132 should be greased
according to the indications on the motor nameplate. Grease
spills from the motor may occur.
Grease specifications: See 11.4.1 Bearing grease.
11.4.1 Bearing grease
Lithium-based grease according to the following specifications
must be used:
• NLGI class 2 or 3.
• Viscosity of basic oil: 70 to 150 cSt at +40 °C.
• Temperature range: –30 °C to +140 °C during continuous
operation.

12. Periods of inactivity and frost protection

Pumps which are not being used during periods of frost should be
drained to avoid damage.
Drain the pump by removing the drain plug. See fig. 24.
Do not tighten the priming plug and replace the drain plug until
the pump is to be used again.
Warning
Pay attention to the escaping liquid which may
cause personal injury or damage to the motor or
other components.
In hot-water installations, special attention
should be paid to the risk of personal injury
caused by scalding hot water.

13. Service

Warning
If a pump has been used for a liquid which is
injurious to health or toxic, the pump will be
classified as contaminated.
If Grundfos is requested to service the pump, Grundfos must be
contacted with details about the pumped liquid, etc. before the
pump is returned for service. Otherwise Grundfos can refuse to
accept the pump for service.
Possible costs of returning the pump are paid by the customer.

13.1 Service kits

Service kits for NB, NBG, see www.Grundfos.com (WebCAPS),
WinCAPS or Service Kit Catalogue.

14. Calculation of minimum inlet pressure

The minimum inlet pressure "H" in metres head required during
operation to avoid cavitation in the pump can be calculated from
the following formula:
H = p x 10.2 – NPSH – H – H
b f
Barometric pressure in bar.
p (The barometric pressure can be taken as = 1 bar.)
b
In closed systems p
b
Net Positive Suction Head in metres head (to be read
from the NPSH curve on page 599 at the highest flow
NPSH the pump will be delivering).
The maximum flow rate must not exceed the values
stated for the individual pump on page 585.
H Friction loss in suction pipe in metres head.
f
Vapour pressure in metres head, see page 605, where
H
v
t = liquid temperature.
m
H Safety margin = min. 0.5 metres head.
s
If the calculated value of H is positive, the pump can operate with
a maximum suction lift of "H" metres.
If the calculated value of H is negative, a minimum suction head
of "H" metres is required. The calculated "H" must be present
during operation.
Example:
p = 1 bar.
b
Pump type: NB 50-200/219, 2-pole, 50 Hz.
Flow rate: 70 m³/h.
NPSH (read on page 599): 2.35 metres head.
H = 3.0 metres head.
f
Liquid temperature: +90 °C.
H (read on page 605): 7.2 metres head.
v
H = p x 10.2 – NPSH – H – H
b f
H = 1 x 10.2 – 2.35 – 3.0 – 7.2 – 0.5 = –2.85 metres head.
This means that a suction head of 2.85 metres is required during
operation.
The inlet pressure calculated in bar: 2.85 x 0.0981 = 0.28 bar.
The inlet pressure calculated in kPa: 2.85 x 9.81 = 28 kPa.
– H
v s
indicates system pressure in bar.
– H [metres head].
v s
25