Flowserve DMX - Manual (Page 25)

DMX/DMXD/DMXH/DMXDH USER INSTRUCTIONS ENGLISH 85392728 - 10/09
Page 25 of 60
A spool piece should be installed in suction
line so that the suction screen may be installed and
removed.
Operation at low flows results in pump
power heating the liquid. A bypass may be required
to prevent vaporization and subsequent pump
damage. Mechanical damage may result from
continuous operation at flows less the minimum flow
of design operating point (see 10.4 Customer Data
Sheet).
When pump is equipped with manifolded
vent and drain lines, each line must be equipped
with an individual valve to prevent any liquid from
a high pressure line flowing into a low pressure
line. These valves must be kept in the closed
position during pump operation.
4.5.2
Suction strainer
In a new installation, great care should be taken to
prevent dirt, scale and welding beads from entering
the pump. Even when piping has been previously
flushed, it is difficult to break loose the oxides and
mill scale, which will become free when the pipe
heats and cools several times. Numerous close
running clearances within the pump are vulnerable to
abrasive matter present in new piping. Foreign
material may be large enough, or of sufficient
volume, to jam a pump, with probable damage to
both pump and drive equipment. Smaller size
material passing through the pump can cause rapid
pump wear and premature pump failure.
This pump is provided with the assumption that it will
be pumping clean liquids (unless otherwise stated in
the order and addressed in the proposal). Flowserve
pumps are provided with running clearances ranging
typically from 0.12 mm (0.005 in.) to 0.80 mm
(0.030 in.), depending on the service and the pump
size. It is impractical to install a suction strainer to
remove particulate of this size. Such particles will
normally pass through the pump without causing
damage, provided the concentrations are minor.
The possibility exists that, on shutdown of the pump,
such particles can become trapped in the close
running clearances during coastdown, causing
binding. Flowserve cannot recommend a procedure
that will totally prevent such binding; however, we
strongly suggest that systems be cleaned and
thoroughly flushed prior to connecting the pump to
the piping to minimize particles entering the pump.
Starting and stopping of the pump should be
MINIMIZED, as pumps are most susceptible to dirt
during starts and stops.
In the event that binding on coastdown occurs, it is
unlikely that the binding can be remedied by hand
rolling the rotor, and partial disassembly may be
required to clean the affected parts. It should be
noted that increased particle concentrations increase
the probability of coastdown binding and seizures, as
well as erosion damage.
Excessive force used to try to free a
bound rotor may cause damage beyond minor clean-
up and repair of rotor parts.
Generally, a pump should not be installed without
start-up strainer protection. The suction piping
should be thoroughly flushed before installing the
suction strainer and connecting the suction piping to
the pump. The strainer should be installed in the inlet
piping near the pump, making certain that it is located
where it may be readily serviced (cleaned). Be sure,
however, that the installed strainer will not distort the
flow to the pump suction nozzle.
Do not install the strainer directly on the pump
suction nozzle. For a cone-type strainer, the down-
stream end of the cone should be no closer than four
(4) pipe diameters from the pump suction nozzle.
Basket-type strainers typically introduce greater flow
disturbances and should be installed at least six (6)
pipe diameters from the pump suction nozzle.
The Flowserve standard for suction strainers consists
of conical-shaped steel plate with 1/8 in. perforations
see the below picture. The open area of the strainer
should be a minimum of three times the area of the
pump suction.
At all times when using suction strainers, it is critical
that the pressure drop across the strainer be
constantly monitored to ensure that the pump suction
PREFERRED DIRECTION OF FLOW