Operating manual for centrifugal pumps AT - TB… - MC… - TC… - TMA
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11.1.5 – Start-up a pump with back pressure at discharge side
In this case a non-return valve must always be installed in the discharge piping.
The unit is started with the discharge valve partially open and after the pump pressure exceeds the back pressure in the
discharge line then is time to adjust the discharge flow regulating valve to attain the operating pressure.
For the Starting Torque of the pump see chapter 19.1.
11.2 - OPERATION
After starting the pump the following should be checked:
- The differential pressure and the capacity are as expected (if required, adjust the flow regulating valve at the pump
discharge side but NEVER throttle the valve at the suction side).
- The motor amperage does not exceed the value shown on the motor nameplate.
- The pump/motor assembly does not have unusual vibrations and noises.
- The seal arrangement works as it should:
if the sealing is by packing there should be continuous dripping from the stuffing box (see chapter 14).
if the sealing is by mechanical seal there should not be any leakage (see chapter 15).
- the bearing housings temperature, when operating regularly, must be lower than 85°C.
CAUTION!
Never run the pump dry.
CAUTION!
Possible contact with high temperature surfaces. Operate only provided with apposite protective devices.
If at start-up there are suspicions of abnormal operation it is recommended to stop the unit and investigate the causes
(see chapter 16).
11.3 - SHUT DOWN
DANGER!
Danger due to collision, crushing or harm. Wait for the complete pump stopping before handling the unit. If the
pump still contains some fluid it may suddenly start to rotate once again. Take precautionary measures by
draining the pump or closing the pipes by mean of a valve. Operate only provided with apposite protective
devices.
The centrifugal pumps can be shut down by switching off the power to the motor, with open or closed flow regulating
valve: however if there are no provisions against liquid hammer it is recommended to close the flow regulating valve at
pump discharge prior to stopping the pump.
Avoid the use of instantaneous shut-off valves, such as solenoid valves. These can cause severe pump damage.
If the piping has not been fitted with non-return valves it is required to close the shut-off valves in sequence to prevent
emptying the piping.
Close first the isolating valve at discharge and then at suction side.
If the non return valve is not fitted, or the isolating valve at the discharge side is not completely closed, it may happen that
during the shut-down the pump shaft will rotate in the opposite direction than is normal because of a return flow: in such
cases absolutely avoid restarting the pump until the pump shaft has stopped rotating.
Following pump shut down it is required to close any auxiliary lines such as flushing, heating, etc.
After the first start-stop and if necessary, check pump/motor alignment and make sure that no external forces or moment
rest on pump or piping.
In the event the pump is shut down for an extended period of time it is recommended to completely drain the pump to
prevent the possibility of freezing in the winter time and/or the possibility of corrosion due to stagnant liquid left in the
pump (see chapter 6).
12 - OPERATING CHECK LIST
Periodically check the good working condition of the pump by reading the instruments such as gauges, amp meters, flow
meters, etc., the pump should constantly be performing as the installation requires.
The operation of the pump should be without abnormal vibrations or noises, if any of these problems is noticed, the pump
should be stopped immediately, search for the cause and make the necessary corrections.
It is good practice to check the pump/motor alignment, the running conditions of the bearings and of the mechanical seals
(see chapters 13 - 14 - 15 - 16) at least once a year, even if no abnormalities have been noticed.
If during operation the pump seems to run irregularly, because of noise or vibrations, it is necessary to stop the
unit and investigate the causes of the malfunctioning (see chapter 16).
When the pump is fitted with auxiliary supply lines such as cooling, heating or flushing it is recommended to periodically
check their flow, temperature and pressure.
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