Flowserve LN - Manual (Page 18)

LN, LNE, LNH, LNV, LNEV, LNC and LNEC USER INSTRUCTIONS ENGLISH 71576423 11-09
Page 18 of 32 flowserve.com
5.7.5 Normal vibration levels, alarm and trip
For guidance, pumps generally fall under a classification
for rigid support machines within the International
rotating machinery standards and the recommended
maximum levels below are based on those standards.
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 two.
These standard values can vary with the rotational
speed and the power absorbed by the pump. For any
special case, contact your nearest Flowserve office.
Measuring vibration at regular intervals will show any
deterioration in pump or system operating conditions.
Vibration velocity –
unfiltered
Horizontal
pumps mm/s
(in./s) r.m.s.
Vertical pumps
mm/s (in./s)
r.m.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)
5.7.6 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) 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 the head available at the
impeller inlet, above the vapour pressure of the
pumped liquid.
NPSH required (NPSH
R
) is the minimum head required
at the impeller inlet, above the vapour 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.