Glossary of Terms and Concepts: M

Magnetic filter -- a filter element which removes additional ferromagnetic particles from the filtered fluid by the action of one or more magnets built into the filter body.
Magnetic plug – solid plug with a magnetic tip protruding into a dynamically circulating part of the oil system. This plug attracts and removes ferromagnetic particles, thus providing a visual condition indicator of the presence of larger iron alloy and similar debris in the oil system. Although it does remove particles, it does not significantly impact oil cleanliness.
Maintenance -- the act of holding or keeping in a preserved state. Specifically, the recurring day-to-day work required to preserve systems and / or their parts in such a condition that they are reliably and consistently available for their intended purpose throughout their normal design life, and beyond. Selected terms and concepts for modern maintenance are:

TERM/CONCEPT	DESCRIPTION
Scheduled maintenance	Performed to reduce the possibility of or prevent the occurrence of a life-limited failure. See preventive maintenance.
Unscheduled maintenance	Performed to reduce the possibility of or prevent the occurrence of a condition failure, or to return a system to serviceability following a condition failure. See corrective maintenance.
Repair	Work required to restore a system or part to a condition substantially equivalent to its originally intended design capacity, efficiency, or capability. It includes the replacement of systems and parts made necessary by incipient or actual failure.
Reliability	Measure of the ability of a component or system to function successfully when required for the period required in the specific environment, without unscheduled outages, expressed as a probability. Reliability is a continuous, multivariate function; unless all variables are known and/or have fixed end points (such as material strength vs load/speed, etc.) then reliability cannot be determined based on the range of a single variable.
Operability	Application-specific critical system term with same general meaning as reliability, generally expressed in 'go / no-go' terms.
Availability	Machine is either operating or in ready-to-operate standby mode. Affected by scheduled and unscheduled maintenance.
Utilization	Actual time that machine is operating. Affected by standby downtime, scheduled and unscheduled maintenance
Maintainability	The probability of preserving a part or system in, or repairing it to, a reliable operable status in a specified period of time under stated conditions using prescribed procedures and / or resources. A system is maintainable if repair time is less than or equal to allowed downtime.
Corrective maintenance	Maintenance initiated only when a failure occurs or performance becomes unsatisfactory in service (also termed reactive maint, see repair).
Preventive maintenance	The planned, scheduled, periodic maintenance initiated to forestall or prevent failures or loss of performance in service. This type of maintenance includes user and vendor requirements and recommendations for inspection, adjustment, cleaning, parts replacement, lubrication, and minor repair and is usually time interval-based.
Predictive maintenance	Testing / inspection procedures performed to identify needs for component lubrication, adjustment, repair or replacement. This technology generates information that is applied to preventive or proactive maintenance goals by assessing performance as it relates to the above factors. Also termed condition monitoring, predictive maintenance is a primary maintenance process which analyzes data on individual items in service and whole populations of systems in order to indicate whether some allocation of technical resources is required.
Proactive maintenance	Changes in design / servicing / operations / maintenance initiated to reduce the total amount of maintenance required and permanently improve reliability and performance through systematically determining and eliminating the root causes of failures.
Reliability-centered maintenance (RCM)	Utilizes data gathered from operational performance (including failures) and predictive, preventive, and proactive maintenance technologies in an integrated manner to increase the confidence that a system or component will operate reliably over an extended life cycle. RCM supports ISO 9000 goals by aiding in the reduction of process variations and the number of shutdown and startup process interruptions.

Manifold – an assembly containing multiple inlet and/or outlet ports and integral relating components servicing more than one area. For example, an intake manifold which delivers air to multiple cylinders, or a filter manifold which directs and collects oil from multiple filter sets.
Manifold filter -- a filter in which the inlet and outlet port axes are at right angles, and the filter element axis is parallel to either port axis.
Matrix – the components of the sample other than the elements of interest. In spectroscopy, the matrix can cause result changes through spectral interference or viscosity change.
Matrix matching – an approach to instrument operation in which the calibrations and standardizations of the instrument attempt to match the major chemical compositions of the standards, blanks, and samples in order to reduce the effect of the sample matrix on the analysis results.
Media migration – portions of the filter medium itself passing into the effluent (downstream) from the filter.
Medium -- the porous material that performs the actual process of filtration.
Media – with respect to filtration, the plural of ‘medium’.
Micron, micrometer (痠) -- a unit of length. One micron = 39 millionths of an inch (.000039"). Contaminant size is usually described in microns. Relatively speaking, a grain of salt is about 60 microns and the eye can see particles to about 40 microns. Many hydraulic filters are required to be efficient in capturing a substantial percentage of contaminant particles as small as 5 microns.
MIL-Spec -- military specification; a guide in determining the quality requirements of products used by the military services, published by the United States Department of Defense.
Mineral oil -- any petroleum oil, as opposed to animal or vegetable-based oils.
Miscible -- capable of being mixed in any concentration without separation of phases; e.g., water and ethyl alcohol are miscible.
Middle distillate -- one of the distillates obtained between kerosene and lubricating oil fractions in the refining processes. These include light fuel oils and diesel fuel.
Motor -- a device which converts fluid power into mechanical force and motion.
Multigrade oil -- an oil meeting the requirements of more than one SAE viscosity grade classification, and may therefore be suitable for use over a wider temperature range than a single-grade oil.
Multigrade oil -- one of the multiviscosity number oils in which one oil combines three SAE viscosity number grades. For example, multigrade SAE 1 OW-40 grade may be used where SAE 1 OW, SAE 20W, SAE 20, SAE 30, or SAE 40 grades are specified. These oils are made possible by improved refining processes and the use of polymer additives.
Multipass or recirculation test -- filter performance tests in which the contaminated fluid is allowed to recirculate through the filter for the duration of the test. Contaminant is usually added to the test fluid during the test. The test is used to determine the beta ratio (relation of pre- to post-filter fluid cleanliness).