Preventive Maintenance: Systematic, Conditional-Based and Forecast
Preventive maintenance is planned technical maintenance, performed regularly at predetermined intervals or according to prescribed criteria on a piece of equipment. The main goal of preventive maintenance is to minimize the likelihood of a machine’s failing. There are three types of preventive maintenance: systematic, condition-based and forecast.
Systematic Preventive Maintenance
The systematic preventive maintenance is of critical importance for the control of the first stages of degradation on a piece of equipment. It is performed at predetermined time intervals or according to a number of units of use, without controlling the general condition of the machine: for example, a specific component of a vehicle’s engine is changed every 3500 miles.
The systematic preventive maintenance requires a solid knowledge of the degradation laws – e.g. service life of a bearing. It should be performed in a highly reliable way, eliminating any need for additional checks between two interventions or for any further monitoring with periodic inspections.
Systematic preventive maintenance is performed on components, that don’t require expensive changing cost. Those include:
- Replacement of oil, filters, bearings, seals, springs, contacts, resistors, bulbs, etc.
- Adjustment of belt tension, pressure, potentiometers fitting, etc.
- Control of levels, tightening tension, etc.
The main drawback of the systematic preventive maintenance is the difficulty to determine the frequency of the needed operations/multiple transactions.
Condition-Based Preventive Maintenance
The condition-based preventive maintenance requires the monitoring of a machine’s functioning or of significant parameters for a certain operation, integrating the resulting actions.
The condition-based preventive maintenance is supposed to overcome the disadvantages of the routine maintenance. It doesn’t require any other additional knowledge than the tolerance limit of the considered physical quantity threshold.
The condition-based preventive maintenance can be continued with the permanent record of the selected parameters or discontinued with the periodic measurements of these parameters.
Preventive Maintenance Forecast
The preventive maintenance forecast is performed according to the extrapolated estimates of the analysis and the evaluation of the significant parameters of a machine’s degradation.
It is a costly maintenance, requiring sophisticated means that applies only to components or operations of critical importance for the machine’s safety and cost. These include:
- Infrared thermography;
- Vibration monitoring (global and spectral analysis);
- Analysis of oils;
- Non-destructive tests: ultrasound, eddy current, acoustic emission, etc.
In conclusion, all three types of preventive maintenance only tend to reduce the probability of failure, but don’t prevent from possible catalectic failure between two interventions.