A–B–C–D–E–F–G–H–I–J–K–L–M–N–O–P–Q–R–S–T–U–V–W–X–Y
M.A.S.T. (Maximum Allowable Stem Torque)
A torque value published by the valve manufacturer of the maximum torque that may be applied to a valve stem before permanent deformation may occur. The actuator maximum torque must not exceed this figure.
Magnetic Particle Test
An inspection procedure for detecting surface cracks and other discontinuities at or near the surface in ferromagnetic materials through the use of fine iron particles in a magnetic field. Techniques and procedures are covered in ASME V, Art. 7 and ASTM E709.
Male Thread
The external thread on pipe, fittings or valves used in making a connection with mating female (internal) threaded parts.
Manifold
A common pipe or chamber having several lateral outlets. Also termed Header.
Mass Spectrometer
An instrument used for sorting streams of electrified particles in accordance with their different masses by means of deflecting fields. The instrument can produce a photographic or graphic record of each compound and the percentage of the compound. Most commonly used in analyzing petroleum and steel products.
MDS (Material Data Sheet)
The material data sheet defines the minimum requirements for the materials, i.e. chemical specifications, manufacturing, qualification of supplier, mechanical testing and properties, non destructive examination, repair, marking and certification.
Mechanical Seal
In a valve a shut-off that is accomplished by a mechanical means rather than with fluid or line pressure. The wedging action of a gate against the seats or the seat springs pushing the seat against the ball or gate are examples of mechanical seals in a valve.
Metal Seated Valve
The sealing contact area is metal to metal between the sealing face of the seat ring and the closure element. For example, in a ball valve, the ball and seats contact and seal area is metal to metal. This is typically used in severe service applications.
Metallizing
The coating of a non-metallic surface with a thin metal layer by spraying, hot dipping or vacuum deposition.
Meter Prover
A system used to check or “prove” a flow meter. A close fitting sphere is launched into a pipe of known inside diameter. The flow medium pushes the sphere through a measured length of pipe between two sphere detection devices. Knowing the transit time and the exact volume between the two stations, a flow rate is calculated and compared with the meter reading.
Meter Run
A section of pipeline in which a meter is installed to measure the volume of fluid passing through the line.
MGO (Manual Gear Operator)
A gear operator that is operated manually with a handwheel.
Mill Certificate
Certificates provided by the steel mill indicating the chemical analysis and physical properties of a specific batch of steel. See Heat Analysis.
Mill Test Reports
See Mill Certificate.
Mill Tests
All tests required by the material specification usually include both the heat analysis (chemical) and the physical properties.
MMCF
An abbreviation for million cubic feet. Used to designate gas volume and gas flow rates in pipelines (MMCF per hour or day).
MOAP
An abbreviation for Maximum Allowable Operating Pressure. Determined in accordance with piping codes, DOT regulations, etc.
Modulating
A term for describing the method of controlling flow through a valve by varying the pressure drop across it.
Modulus
The stress required to produce a certain elongation (strain) usually 100%. In elastomers it is a good indication of toughness and resistance to extrusion. Also termed Tensile Modulus.
Mold
A hollow cavity (frequently in packed sand) for giving a desired shape to a material in a molten or plastic state. Used in making metal castings.
Monitoring – Monitor Service
A field procedure whereby two valves (usually regulators) are installed in series and adjusted in such a manner that, should the primary regulator fail, the standby regulator will automatically take over at a slightly higher pressure setting.
Motor
A device which converts electric, pneumatic or fluid power into mechanical force and motion, normally a rotating shaft output.
MSS (Manufacturers Standardization Society of the Valve and Fitting Industry)
A technical organization dedicated to the technical needs of the valve and fittings industry. Standards and codes are written and revised by technical committees and address topics such as valves, valve actuators, pipe fittings, flanges, and pipe hangers. Recommendations of this society are advisory only. www.mss-hq.com
MWP (Maximum Working Pressure)
The maximum working pressure at which a valve can be operated.
|
ANSI Class |
MWP (CWP) |
|
150 |
275 psi |
|
300 |
720 psi |
|
400 |
960 psi |
|
600 |
1440 psi |
|
900 |
2160 psi |
|
1500 |
3600 psi |
|
2500 |
6000 psi |