Difference Between Preventive and Predictive Maintenance

Difference Between Preventive and Predictive Maintenance

If you don't know the actual definitions, you will confuse them with each other, or even with something totally different. Learn more on the similarities and differences between preventive and predictive maintenance.
Maintenance is considered wholly as a function of a company and its tools. It is the very difference between the success and failure of any project when it comes to making those machines work. You may have the most skilled labor to get the job done, but making any compromise in the maintenance department will be something to regret.

Apart from preventive maintenance (PM) and predictive maintenance (PdM), there are also corrective maintenance (CM), improvement maintenance (IM) and run to failure maintenance (RTF). For now, we will only look at the first two and their relation with the machinery and each other.

Preventive Maintenance
Preventive maintenance means taking precautions over a machine before anything happens to it. It is done on a machine when it is shut down for all maintenance reasons. It is done with the total period of functionality of the machine in view. We perform preventive maintenance on any machine to minimize its faults and maximize outputs. It's done such that there is little or no possibility of the machine breaking down in the future. All in all, preventive maintenance, prevents excessive deterioration of a component, a machine or a system and lowers the damage to an acceptable level. So what we are doing is keeping the machine condition as close to its initial conditions (known as the optimum conditions) as possible.

Predictive Maintenance
It is the repairing of a machine before any failure occurs. If you are performing a predictive maintenance, what you would be doing is checking the parts of a machine and repairing any faults or the precursors to a fault. It is not totally time based. It pays more attention to the run-time or total usage of a machine. Predictive maintenance is used to minimize the maintenance cost and maximize the total run-time of a machine. An example would be changing the oil in vehicles every 3,000 to 5,000 miles. You're not really checking the vehicle for any oil related problems, you're just replacing the oil based on prior knowledge or the mechanics advice. Therefore, predictive maintenance is based on the knowledge of a system. The more you know about something, the better you'll be at performing it.

Points of Difference

Predictive Maintenance Preventive Maintenance
Predictive maintenance works on avoiding any possible failure of the machine, including failure to a certain extent or any catastrophic failures to the maximum possible extent. Preventive maintenance works on keeping the machine as close to optimum conditions as possible, thereby excluding the need to repair the machine and eliminating all failures, except catastrophic failures.
Predictive maintenance does not need any extra labor force or increased working of employees. This potentially increases worker morale as they don't have to work extra periodically.

You also don't need any such kit as the maintenance concentrates on relieving stress elements in the machine rather than constant monitoring.
Preventive maintenance requires more labor since it is labor intensive. It is timed, so you need a proper schedule of company timings. This means constantly having to work on the machine conditions.

You will also need a good maintenance kit for all the periodic offline repairs.
Predictive maintenance is carried out according to the usage-time or run-time of the machine. The time gap between two instances can vary as per the usage of a machine. Preventive maintenance is carried out periodically on the machine, regardless of its working condition, even if it is in optimum conditions. It is a scheduled process, timed according to the periods of the machine's usage.
Need for Information
Naturally, the amount of information required by maintenance heads will be much more for predictive maintenance. This is because it focuses on removing faults rather than avoiding them. The information required per person is lesser in case of preventive maintenance, as each individual or team is assigned the same repetitive process of maintenance for every machine.
The investments are more in terms of diagnostic equipment and training. The investments are in terms of skilled labor and maintenance equipment.
Profits and Losses
Predictive maintenance is more profitable than preventive maintenance. This is because of the lesser downtime of a machine. It only needs to be shut down in case of large failures. For most other times, it only takes care of predicting an error and fixing its cause. Preventive maintenance suffers a loss when compared to predictive maintenance. This has everything to do with the constant maintenance cost required.
Predictive maintenance is better in terms of total profits, the only problem being the total expertise needed for the entire operation. The total profits can be more than preventive maintenance by 8% to 12%, with lesser or no breakdowns of machines comparatively. Losses occur here due to the increased work force required, along with the inability to even slightly reduce the chances of catastrophic failures. Preventive maintenance gains savings only from a point of view of average failures and total capital cost.

All in all, predictive maintenance turns out the better of the two options when it comes to average savings. But if you want a system to work on optimum conditions at all times, you need to perform preventive maintenance. For anything else, predictive maintenance is the way to go.