Page 25 - RCM - A practical Guide_V1

RCM - A Practical Guide

1 - Defining functions

Primary function
The function that the asset was designed for or the function that is required i.e. the WANT.
For example:
❑ A car braking system has the primary function to stop the car.
❑ A boiler has the primary function to heat water.
None of these will be the item’s only function and most complex items possess several. Also the
amount of information given in these statements is insufficient to establish when each has failed. For
instance:
❑ What distance is required to stop the car under specific conditions?
❑ How much water is the boiler required to heat and how long should it take?
A clearer definition of the functions may be:
❑ The car braking system must be capable of stopping the car within 100 metres on a dry
surface and to achieve this at its gross vehicle weight.
❑ The boiler may need to heat 100l of water to 100°C in 30 minutes.
These statements make it easier for the analyst to determine when the item under analysis fails to
achieve the required standard of performance.
Secondary function
Something the asset can do in addition to its primary function.
For example:
❑ The car braking system may provide an anti-skid facility and have a parking brake capability.
❑ The boiler may have a facility to display the level of contents or be able to automatically
shut off when the desired temperature is achieved.
❑ These functions may be less obvious than the primary function but in the operating context
are still important.
Secondary functions should consider the following:
E nvironmental integrity

S afety/structural integrity
C ontrol/containment/comfort
A ppearance
P rotective devices and systems
E conomy/efficiency
S uperfluous functions

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