It is the arithmetic average of the absolute values of the profile deviations from the mean line of the roughness profile. Statistically very stable repeatable parameter good for random type surface such as grinding. Not a good measure of sealed surfaces.
See Venturi Valve.
A throttling or pressure-reducing valve which exercises automatic control over some variable (usually pressure). Not an on-off valve.
A term usually applied to plug valves. The “regular” port of such a valve is customarily about 40% of the line pipe area. Hence it corresponds to a venturi or reduced bore valve of like nominal pipe size. Venturi ball valves are often a logical alternative to plug valves with advantages in price, torque and low maintenance.
The probability that a device will operate correctly over a specified period or amount of usage.
The operation of a valve or other flow control devices from a point at a distance from the device being controlled. Can be accomplished by electrical, pneumatic or hydraulic means.
The closeness of the band of measurements of repeated measurements of the same variable under the same operating conditions.
In hydraulic systems, it is the storage tank for unpressurised fluid from which the pump draws its supply. It is also the vessel to which the return lines are connected.
A valve seat containing a soft seal such as an O-Ring or a plastic insert to assure tight shut-off.
The time between an instruction to proceed with an action to the completion of the task.
The raised area of a flange face which affords a seal with a mating flange face by means of a flat gasket of the same diameter as the raised face. RF flanges seal with a flat gasket made of materials designed for installation between the raised faces of two mating flanges (both with raised faces). The raised faces have a prescribed texture to increase their gripping and retaining force on this flat gasket. Some users of raised face flanges specify the use of spiral wound gaskets.
A metal gasket shaped like a ring with a number designation, designed to fit into grooves machined into the face of flanges and/or other connectors and provide a seal after make-up.
A single-seated ball valve that is designed to seal by using the valve’s stem to mechanically wedge the valves ball into a stationary seat, effecting a bubble tight seal. The valve stem operates through a quarter turn of rotation as the stem is raised or lowered by the operator. The mechanical action of the stem moves the ball away from the seat prior to the 90° rotation of the ball. This design preserve the seat as it is never in contact with the ball during valve stroking.
A valve stem which rises as the valve is operated.
It is the largest of five roughness depths measurements. Useful for surfaces where a single defect is not permissible, e.g. a seal with single scratch.
It is the root mean square average of the profile height deviations from the mean line of the roughness profile. More sensitive to peaks and valleys than Ra because the amplitudes are squared.
A hardness measurement based on the net increase in depth of impression as a load is applied. Hardness numbers have no units. The type of indenter and the test load determine the hardness scale (A, B, C, etc). The higher the number in each of them, the harder the material. The indenter may either be a steel ball of some specified diameter or a spherical diamond-tipped cone of 120° angle and 0.2 mm tip radius. ASTM D785 is the standard test for determining the Rockwell hardness of plastics and electrical insulating materials.
Small scale variations in the height of a physical surface. Roughness is measured by sampling and statistical techniques, whereby different parameters are used. ISO 4287 and ASME B46.1 provide terms, definitions, measurement methods and surface texture parameters.
Rotational speed turns per minute. For example, the RPM delivered by a power operator to the pinion shaft of a gear operator.
An X-ray, NDE Procedure for locating flaws in welds, forgings, castings and fabricated parts. Techniques and procedures are covered in ASME V, Art. 2.
A flange connection using a specially shaped soft metal ring as a gasket. Generally used on high pressure valves and not widely used in the pipeline industry. RTJ flanges have grooves cut into their faces which accept steel ring gaskets. RTJ flanges seal when tightened bolts compress the gasket between the flanges into the grooves deforming (or “coining”) the gasket to make intimate contact inside the grooves creating a metal-to-metal seal. An RTJ flange may have a raised face with a ring groove machined into it. This raised face does not serve as any part of the sealing means for RTJ flanges that seal with BX ring gaskets. The raised faces of the connected and tightened flanges may contact each other. In this case the compressed gasket will not bear additional load beyond the bolt tension vibration and movement cannot further crush the gasket and lessen the connecting tension.
A pressure-relief device employing a relatively thin one-time-use membrane designed to fail at a specified pressure. Once the membrane, usually a metal foil has failed, it will not reseal and has to be replaced. They are often used as backup device for a conventional safety valve.
It is the mean of the distance between the highest and lowest points of five successive sample lengths of the roughness profile. More sensitive than Ra to changes in surface finish, as maximum profile heights and not averages are being examined.
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