Flowserve Gearex Rotary Gear Pumps External and Internal Bearing - Manual (Page 34)

EXTERNAL GEAREX USER INSTRUCTIONS ENGLISH 71569246 (2167B-E1)
Flowserve Pump Division 34
®
5.11.3 Net positive suction head (NPSH
A
)
NPSH available (NPSH
A
) is a measure of the head or
energy available in the pumped liquid, above its
vapour pressure, at the pump suction branch.
NPSH required (NPSH
R
) is a measure of the head
required in the pumped liquid, above its vapour
pressure, to prevent vaporization of the liquid. This
phenomenon, called cavitation, can cause serious
damage to the pump and adversely affect
performance. It is important that NPSH
A
> NPSH
R
to
avoid vaporization of the liquid. The margin between
NPSH
A
> NPSH
R
should be as large as possible.
NPSH
A
is affected by changes in the liquid
temperature and vapour pressure, the altitude of the
installation, entrained gasses in the liquid, and the
viscosity of the liquid.
If any change in NPSH
A
is proposed, ensure these
margins are not significantly eroded. Refer to the
pump performance curve to determine exact
requirements particularly if flow has changed. If in
doubt please consult your nearest Flowserve office
for advice and details of the minimum allowable
margin for your application.
5.11.4 Pumped flow
Flow must not fall outside the minimum and
maximum continuous safe flow shown on the pump
performance curve and/or data sheet.
5.11.5 Pressure surges
The pump must not be subjected to pressure surges
such as may be caused by waterhammer or sudden
check valve closure.
6 MAINTENANCE
6.1 General
It is the plant operator's responsibility to ensure
that all maintenance, inspection and assembly work
is carried out by authorized and qualified personnel
who have adequately familiarized themselves with
the subject matter by studying this manual in detail.
(See also section 1.6.2 Personnel qualification and
training.)
Any work on the machine must be performed when it
is at a standstill. It is imperative that the procedure
for shutting down the machine is followed, as
described in section 5.10 Stopping and shutdown.
On completion of work all guards and safety devices
must be re-installed and made operative again.
Before restarting the machine, the relevant
instructions listed in section 5 COMMISSIONING,
START-UP, OPERATION AND SHUTDOWN must be
observed.
Oil and grease leaks may make the ground
slippery. Machine maintenance must always
begin and finish by cleaning the ground and the
exterior of the machine.
If platforms, stairs and guard rails are required for
maintenance, they must be placed for easy access to
areas where maintenance and inspection are to be
carried out. The positioning of these accessories
must not limit access or hinder the lifting of the part to
be serviced.
When air or compressed inert gas is used in the
maintenance process, the operator and anyone in the
vicinity must be careful and have the appropriate
protection.
Do not spray air or compressed inert gas on skin.
Do not direct an air or gas jet towards other people.
Never use air or compressed inert gas to clean
clothes.
Before working on the pump, take measures to
prevent an uncontrolled start. Put a warning board
on the starting device with the words:
"Machine under repair: do not start".
With electric drive equipment, lock the main switch
open and withdraw any fuses. Put a warning board
on the fuse box or main switch with the words:
"Machine under repair: do not connect".
Never clean equipment with inflammable solvents or
carbon tetrachloride. Protect yourself against toxic
fumes when using cleaning agents.
6.2 Maintenance schedule
It is recommended that a maintenance plan
and schedule is adopted, in line with these User
Instructions, to include the following:
a) Any auxiliary systems installed must be
monitored, if necessary, to ensure they function
correctly.
b) Gland packings must be adjusted correctly to
give visible leakage and concentric alignment of
the gland follower to prevent excessive
temperature of the packing or follower.