1.6 Care and maintenance of pumps
Care and maintenance of pumps
The first prerequisite for long service life and reliable operation of a pump unit is naturally, as applies to all types of machinery, that the pump should not be subjected to working conditions other than those for which it was designed. The second is that the unit should receive the necessary care and maintenance. This is not generally carried out to preserve a certain economic value but to maintain reliability of operation. In the selection of pumps, the planning of installations, etc., it is essential to take account of the maintenance aspects. The assessment of a particular pump should be based on technical grounds connected with maintenance (possibilities of dismantling, availability of spare parts, etc.). Further, steps must be taken to ensure that connected pipe sections can be loosened easily, that working space, hoisting facilities and free transport routes are available.
The distinction between servicing and care, on the one hand, and preventive maintenance, on the other, is difficult to draw. However, in the text which follows these activities will be dealt with under the headings “Inspection and care” and “Maintenance and overhauls” respectively. The aim of care and maintenance is, of course, to prevent as far as possible sudden breakdowns with costly standstills and subsequent process plant operational problems etc.
The necessary amount of care and maintenance is difficult to estimate. Factors such as the need of reliability of operation, the properties of the liquid pumped, the working environment of the pump, etc., exercise a marked influence in this respect. In general it can be recommended that care as well as maintenance should be incorporated into regular routines and that some form of record of faults noted and measures taken should be drawn up. It is rational policy to make out a document suitable (machine card or similar) for every pump unit. This document should be linked to the drawings, specifications, working instructions and spare parts lists which should always included in every pump delivery. It should perhaps be noted that these documents should be in the hands of the working staff, not locked away in some inaccessible file. In modern time, all well managed production facilities have implemented computerized maintenance systems where all information about their rotating machinery can be found and each machine can be analysed.
Recording faults and measures taken in the pump documents makes it possible to draw up a basis for determining with greater accuracy intervals for care and maintenance of pumps. It also provides the basis for cost control. It is estimated
that the annual maintenance costs of a pump unit including spare parts amount to between 10% and 20% of the purchase cost of the unit. The tables in figures 1.6.1, 1.6.2 and 1.6.3 review some practical cases of pump faults and their frequency of occurrence. These give us some idea as to the types of functional troubles to be anticipated.
A general conclusion to be drawn from the tables in figures 1.6.1, 1.6.2 and 1.6.3 may be that faults in the pump are much more common than in couplings or motors. Faults affecting bearings and packing´s are of relatively high frequency in the pump, as are also blockages and damage to impellers when troublesome liquids are pumped. A control study of a sewage disposal plant with about 250 pumps in operation in pumping stations and purification plants yielded much the same results.
Figure 1.6.1-3 List of faults experienced by a large of pumps of different types used in the cellulose industry.
See also section Maintenance and repair of pumps >>>