Page 26 - RCM - A practical Guide_V1

RCM - A Practical Guide

The acronym ‘ESCAPES’ is a useful prompt.

Protective function
A protective function is the function of a device which is designed to avoid, eliminate or minimise the
consequences of failure of another related function.
These devices can operate in a variety of different ways.
For example:
They may provide:

❑ An automatic cut-out if failure occurs:
an overheat sensor may work in this way and shut down the equipment to prevent further
damage.
❑ A standby role to take over if the primary function fails:
backup devices such as standby generators or backup hydraulic pumps etc
❑ Indications to the operator so remedial action can be taken:
audible warnings, warning lights, pressure gauges etc.
❑ Functions which can eliminate an undesirable situation:
relief valves, fire extinguishing equipment etc.
❑ A means to prevent dangerous situations in the first place:
warning signs, protective covers etc.
Equipment has become more complex and the wealth of protective devices has grown with this
complexity. Many are automatic devices designed to reduce or eliminate the effects of a failure or
backup devices incorporated as part of design to protect a critical function.

Superfluous function
Superfluous functions usually happen when the equipment or the way in which it is operated is
modified over a period of years or when new equipment has been over specified. Those items are
often costly to remove and remaining in the system is the cost effective option, however, they can fail
and reduce the overall reliability of the system.
Because of this some could require maintenance to ensure that the consequences of their failure are
not experienced.
An example of a superfluous function may be that of a pressure relief valve for a system whose
operating pressure has been reduced to much lower levels. Although the relief valve is now not used it
may still corrode and leak affecting the system operation. Maintenance may be required to look for
corrosion.
Describing the Function
As can be derived from the paragraphs above, all function statements should contain a verb, an object
and a performance statement, the latter should be quantified if possible.
In the example above:

To stop the car within 100 metres on a dry surface and to achieve this at its
gross vehicle weight.

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