1.6.2 Maintenance and repairs of pumps
Maintenance and repairs of pumps
Maintenance in this context refers to preventive maintenance intended to reduce the number of breakdowns involving the resultant stopping the pump. Attempts have been made to work out optimum maintenance statistics for pumps, but the results are uncertain and the systems are difficult to handle. Preventive maintenance, in addition to the measures called for as the result of the faults found during inspections, usually includes the following:
- Maintenance of packing boxes and seals
- Lubrication of bearings
- Repairs / Overhauls of different kinds
The care of soft packings and mechanical seals are important items of preventive maintenance. Section 1.6.4 contains a list of common faults in packing boxes as well as of causes and the appropriate measures to be taken.
Mechanical seals, correctly selected and installed, normally have a relatively long service life span, 3-5 years at reasonable pressures, and they require no special maintenance. However, regular checks are necessary in order to make early diagnoses of faults and to ensure that flushing liquid, if used, is freely supplied. See further information about seals in Chapter 5 Pump Seals.
Bearing lubrication should be carried out according to instructions obtained from the pump supplier. Overhauls imply taking the pump to pieces and examining all parts. In the case of pumps working with abrasive media or other difficult liquids, overhauls must be carried out relatively frequently, possibly every year. Standard process pumps and sewage pumps usually require overhauls at intervals of 3-5 years. For pumps handling clean water the intervals can be still further extended.
During overhauls the pump is cleaned internally and externally. Bearings and other items subject to wear are checked and where necessary replaced. Wear ring clearance should be checked. This should not exceed 1 mm, clearance in new pumps are normally less (0,3mm) but depends on size, as the hydraulic efficiency of the pump is adversely affected if the clearance exceeds this figure. The impeller and the pump casing are checked with respect to deposits, cavitation and corrosion damage. If the impeller is damaged it must be replaced. An impeller in poor condition means a drastic reduction of pump performance. Pump overhauls are expensive and it is necessary to consider whether they should be carried out more than a few times. In the case of small and simple pumps it is usually more profitable to replace the pump than to perform a complete overhaul.