Flowserve MENBLOC - Manual (Page 24)

MENBLOC USER INSTRUCTIONS ENGLISH 71576296 - 02/13
Page 24 of 40 flowserve.com
When ambient temperatures are
likely to drop below freezing point, the pump and
any cooling and flushing arrangements must be
drained or otherwise protected.
5.6.4 Restarting in continuous running
a) Ensure that the pump is completely full of
liquid.
b) Ensure a continuous supply with a sufficient
available NPSH.
c) Ensure a backpressure so that the motor
power is not in excess.
d) Respect the starting frequency
imposed by the motor manufacturer.
e) Protect the pump against water hammer
when stopping or starting.
To reduce any possibility of motor thermal stress,
the number of motor starts per hour given in the
table below must not be exceeded:
IP 55 motor – An extended motor shaft
≤
1.2 kW - 35 starts/hour
1.5 to 3.3 kW - 30 starts/hour
4 to 4.6 kW - 25 starts/hour
6.5 kW - 20 starts/hour
8.2 to 16 kW - 15 starts/hour
IP 55 motor – An added pump shaft
1450 min
-1
15 kW
22 kW
30 kW 5 starts/hour
2900 min
-1
18.5 kW
22 kW
30 kW
37 kW
The time periods between each start up should be
roughly equal in any one-hour period.
5.7 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.
5.7.1 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.
5.7.2 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.
5.7.3 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.
5.7.4 Net positive suction head (NPSH
A
)
NPSH available (NPSH
A
) is the head available at
the impeller inlet, above the vapor pressure of the
pumped liquid.
NPSH required (NPSH
R
) is the minimum head
required at the impeller inlet, above the vapor
pressure of the pumped liquid, to avoid excessive
cavitation and extreme performance degradation.
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.
5.7.5 Pumped flow
Flow must not fall outside the minimum and
maximum continuous safe flow shown on the
pump performance curve and or data sheet.
5.8 Pumps for Food Use or Potable
Water
If the pump has not been specifically ordered for a
food or drinking water application it must not be
used for these types of applications. If it has been
ordered for this type of application the following
recommendations are to be followed.