The Reliability Properties of Parallel System Arrangements for the Utmost Plant and Equipment Reliability

Equipment in parallel system arrangements have two reliability properties that arise because they are a parallel system.

These properties lead to three valuable business and operational implications you must consider when you use equipment in parallel configurations.


Slide 36 – The Reliability Properties and Business Implications of Parallel System Arrangements to Get Maximum Plant and Equipment Reliability


In parallel system arrangements there is always more than one way to produce the output of the system. When one item fails in a parallel system a second item takes over the duty, and the system continues to operate.

Shown at the top of the above slide is a parallel system arrangement of equipment. The equation applies to a parallel system in which each individual equipment can service the duty required of the system. Such a configuration is known as a “fully active arrangement.”

There are other parallel system arrangements, such as duty-and-standby configuration where a second unit is ready to over when the working unit fails. Two-of-three, in which two items of equipment from a group of three must always operate to deliver the system output. And three-of-four, where three from a group of four must operate to deliver the full-service duty. Each arrangement has its applicable parallel system reliability equation to determine the system reliability.

Implications of Parallel System Arrangements

There are two properties that apply to parallel system arrangements. The first is, the more components in parallel the greater is the system reliability. As more items are added in parallel there are more ways the output can be sustained when one item fails.

The second property is, the reliability of a parallel arrangement is higher than the most reliable item in the arrangement. Putting things in parallel delivers the greatest system reliability possible.

Getting the Benefits of Parallel System Arrangements

The two properties produce important business implications. You use parallel systems when the risk from failure of equipment in series is unacceptable. Use a parallel configuration to greatly reduce series system risk where business, operational, and safety risk is high. So, if one item fails a second or third item is ready to continue the service duty.

A second implication is to intentionally provide options in a series process to continue operation if an equipment item fails. For example, include connection points and tie-ins to processes where mobile plant, such as air compressors, mobile power supplies, process pumps, etc., can be quickly connected to continue production.

Thirdly, take on the mindset of building redundancy into all things you do. Give yourself many options to be successful. When one thing goes wrong you have a second solution already in place. Setting-up parallel system arrangements makes your life and work far more certain to be successful, and very much less stressful.


This slide is a companion to the new Industrial and Manufacturing Wellness book. The book has extensive information, all the necessary templates, and useful examples of how to design and build your own Plant Wellness Way enterprise asset life cycle management system-of-reliability. Get the book from its publisher, Industrial Press, and Amazon Books.

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