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6.26
Irrigation User’s Manual
therefor is that when the pump is not switched on at closed valve, it then pumps at a low pump
head, causing a high pump-delivery that can lead to overloading and even damage to the motor. If
Escom power is used, it will also keep the kVA demand low. Open the cooling water on the
mechanical seals and bearings if they are part of the unit. Switch on the pump. As soon as the
pump runs on full speed and the required pump head is reached, the sluice valve can be opened
slowly. Check the reading on the ampere meter to ensure that the permissible value is not
exceeded.
The pump must not be allowed to operate at closed valve for too long, since overheating can occur.
If the pump has been provided with an axial flow impeller, the drive requirement and downstream
pressure will drop if the delivery increases. A stop valve is therefor not necessary. Where a
number of pumps are served from one transformer, it is also important to switch on the pumps in
order of large to small. It also keeps the kPa demand peak low.
8.3 Switching off the pumps
It is advisable to close the sluice valve just before switching off the pump, because it combats
water hammer and will also keep water in the pipes that can possibly be used for the next deaeration of the pump. Also close the small valve that closes off the vacuum meter on the suction
side before the pump is switched off.
9 Maintenance of pumps
The pump manufacturer usually provides a maintenance schedule that indicates the maintenance to be
done. As with any type of equipment, it is very important that the necessary maintenance is done
regularly to ensure that the installation can function efficiently and that the life span of the installation
is prolonged. The pump must always run smoothly without any vibrations. The water depth on the
suction side as well as the power consumption must also be regularly monitored.
Over and above the manufacturer’s schedule, the following can serve as directives for the maintenance
of the centrifugal pumps:
•
Check the alignment every six months
•
Replace the oil every six months if applicable. If the oil level drops, new oil must be added
•
Check and clean the bearings every 1 000 operating hours
•
Inspect all wearing parts regularly and do a hydraulic test. A simpler test can also be done by just
closing the sluice valve and taking a reading on the pressure meter that is installed upstream of
the sluice valve. If the pressure drops in relation to when the pump was initially installed, it
indicates excessive wear. This test should be sufficient for maintenance purposes. If there is a
suspicion that the installation does not function correctly, the complete test can be done, as
described in Section 6. By monitoring the ampere reading, it can be determined whether the
pump’s service point changes with time.
•
Inspect the gland leakage regularly. It must leak slightly, because it is lubricated by water. Also
feel the pump for excessive vibrations.
It is also worthwhile to dismantle the pump sometimes and to concentrate on the following:
•
Impeller clearance at collar – skim the impeller neck to give clearance and mount the correct
wear rings.
•
Inspect the pump shaft for damage
•
Replace casings f necessary
•
Clean surfaces of impellers, pump casing, etc., paint if necessary
•
Replace gaskets and O-rings and bearings
•
Check all adapter parts.
The following table can be used as directives for maintenance of centrifugal pumps: