Flowserve LNGT - Manual (Page 28)

LNGT USER INSTRUCTIONS ENGLISH 00083107 02-08
Page 28 of 48
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Motor rating kW [hp] Maximum stop/starts per hour
Up to 15 [20] 15
Between 15 [20] and 90 [120] 10
90 [120] to 150 [200] 6
Above 150 [200] Refer
Where duty and standby pumps are installed it is
recommended that they are run alternately every
week.
5.8 Stopping and shutdown
a) Close the outlet valve, but
ensure that the pump runs in this condition for
no more than a few seconds.
b) Stop the pump.
c) Switch off flushing and/or cooling/heating liquid
supplies at a time appropriate to the process.
d) For prolonged shut-downs and
especially when ambient temperatures are
likely to drop below freezing point, the pump
and any cooling and flushing arrangements
must be drained or otherwise protected.
5.9 Hydraulic, mechanical and
electrical duty
This product has been supplied to meet the
performance specifications of your purchase order,
however it is understood that during the life of the
product these may change. The following notes
may help the user decide how to evaluate the
implications of any change. If in doubt contact your
nearest Flowserve office.
5.9.1 Specific gravity [SG]
Pump capacity and total head in meters [feet] do
not change with SG, however pressure displayed
on a pressure gauge is directly proportional to SG.
Power absorbed is also directly proportional to SG.
It is therefore important to check that any change in
SG will not overload the pump driver or over-
pressurize the pump.
5.9.2 Viscosity
For a given flow rate the total head reduces with
increased viscosity and increases with reduced
viscosity. Also for a given flow rate the power
absorbed increases with increased viscosity, and
reduces with reduced viscosity. It is important that
checks are made with your nearest Flowserve
office if changes in viscosity are planned.
5.9.3 Pump speed
Changing pump speed effects flow,
total head, power absorbed, NPSH
R
, noise and
vibration. Flow varies in direct proportion to pump
speed, head varies as speed ratio squared and power
varies as speed ratio cubed. The new duty, however,
will also be dependent on the system curve. If
increasing the speed, it is important therefore to
ensure the maximum pump working pressure is not
exceeded, the driver is not overloaded, NPSH
A
>
NPSH
R
, and that noise and vibration are within local
requirements and regulations.
5.9.4 Net positive suction head [NPSH
A
]
NPSH available [NPSH
A
] is a measure of the head
available in the pumped liquid, above its vapor
pressure, at the pump suction branch.
NPSH required [NPSH
R
] is a measure of the head
required in the pumped liquid, above its vapor
pressure, to prevent the pump from cavitating. It is
important that NPSH
A
> NPSH
R
. The margin
between NPSH
A
> NPSH
R
should be as large as
possible.
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.
5.9.5 Pumped flow
Flow must not fall outside the minimum and
maximum continuous safe flow shown on the pump
performance curve and or data sheet.
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.]
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 5.8.
On completion of work all guards and safety
devices must be re-installed and made operative
again.