6 stopping and shutdown, 7 hydraulic, mechanical and electrical duty – Flowserve NMD User Manual

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Page 21 of 40

Alarm and trip values for installed

pumps should be based on the actual
measurements (N) taken on site on the bearing
housings of the pump in the fully commissioned as
new condition.

The example (N) value is given for the preferred
operating flow region (typically this may extend to 70
to 120 % of the pump best efficiency point); outside
the preferred flow region the actual vibration
experienced may be multiplied by up to 2.

These standard values can vary with the rotational
speed and the power absorbed by the pump. For
any special case, do not hesitate to consult us.

Measuring vibration at regular intervals will then
show any deterioration in pump or system operating

Vibration Velocity -




mm/s (in./s)




mm/s (in./s)


Normal N

5.6 (0.22)

7.1 (0.28)

Alarm N x 1.25

7.1 (0.28)

9.0 (0.35)

Shutdown Trip N x 2.0

11.2 (0.44)

14.2 (0.56)

5.5.6 Stop/start frequency
Pump sets are normally suitable for the number of
equally spaced stop/starts per hour shown in the
table below. Check actual capability of the driver and
control/starting system before commissioning.

Motor rating kW (hp)

Maximum stop/starts

per hour

Up to 15 (20)


Between 15 (20) and 90 (120)


90 (120) to 150 (200)


Above 150 (200)


Where duty and standby pumps are installed it is
recommended that they are run alternately every

5.6 Stopping and shutdown

5.6.1 Stopping and restarting in continuous
According to hydraulic conditions of the installation
and its automation degree, stop and restart
procedures can have different forms. Nevertheless
all of them must respect imperatively the following

a) Avoid that the unit turns in the opposite direction

to the normal running.

b) Make sure that the discharge line pressure does

not reach the foot valve.

c) Avoid a continuous running below the authorized

flow rate (see § 5.4.2).

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.


Respect the starting frequency

imposed by the motor manufacturer.


Protect the pump against water hammer

when stopping or starting.


Close the outlet valve and stop the

motor. Eventually close the inlet valve.

For prolonged shutdowns 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.

5.7 Hydraulic, mechanical and electrical

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.

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