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TAG CLOSED TESTER - apparatus for determining the flash point of petroleum liquids having a viscosity below 5.8 centistokes (cSt) at 37.8°C (100°F) and a flash point below 93°C (200°F), under test methods prescribed in ASTM D 56. The test sample is heated in a closed cup at a specified constant rate. A small flame of specified size is introduced into the cut through a shuttered opening at specified intervals. The lowest temperature at which the vapors above the sample briefly ignite is the flash point. See Pensky-Martens closed tester.

TAG OPEN CUP - apparatus for determining the flash point of hydrocarbon liquids, usually solvents, having flash points between -17.8° and 168°C (0° to 325°F), under test methods prescribed in ASTM D 1301. The test sample is heated in an open cup at a slow, constant rate. A small flame is passed over the cup at specified intervals. The lowest temperature at which the vapors above the sample briefly ignite is the flash point. See Cleveland open cup.

TEL (TETRAETHYL LEAD) - see lead alkyl.

TEMPERATURE SCALES - arbitrary thermometric calibrations that serve as convenient references for temperature determination. There are two thermometric scales based on the freezing and boiling point of water at a pressure of one atmosphere: the Fahrenheit (F) scale (32° = freezing, 212° = boiling) and the Celsius (C) or Centigrade, scale (0° = freezing, 100° = boiling). Additionally, there are two scales in which 0° = absolute zero, the temperature at which all molecular movement theoretically ceases: the Kelvin (°K), or Absolute (°A), scale and the Rankine (°R) scale, which are related to the Celsius and the Fahrenheit scales, respectively (0°K = -273.16°C; 0°R = -459.69°F). The four scales can be related to each other by the following formulas:

°C = 5/9 (°F-32)        °F = 9/5 °C + 32
°K = °C + 273.16      °R = °F + 459.69

Another scale based on the thermometric properties of water is the Reaumur scale in which the freezing point is set at 0° and the boiling point at 80°. This scale has only limited application.

TEMPORARY VISCOSITY LOSS (TVL) - measure of decrease in dynamic viscosity under high shear rates compared to dynamic viscosity under low shear. May be applied to fresh oil or used oil.

THERMAL CRACKING - in refining, the breaking down of large, high-boiling hydrocarbon molecules into smaller molecules in the presence of heat and pressure. See cracking.

THIXOTROPY - tendency of grease or other material to soften or flow when subjected to shearing action. Grease will usually return to its normal consistency when the action stops. The phenomenon is the opposite of that which occurs with rheopectic grease. Thixotropy is also an important characteristic of drilling fluids, which must thicken when not in motion so that the cuttings in the fluid will remain in suspension.

TIMKEN EP TEST - measure of the extreme pressure properties of a lubricating oil. The test utilizes a Timken machine, which consists of a stationary block pushed upward, by means of a lever arm system, against the rotating outer race of a roller bearing, which is lubricated by the product under test. The test continues under increasing load (pressure) until a measurable wear scar is formed on the block. Timken OK load is the heaviest load that a lubricant can withstand before the block is scored. See scoring.

TORQUE FLUID - lubricating and power-transfer medium for commercial automotive torque converters and transmissions. It possesses the low viscosity necessary for torque transmission, the lubricating properties required for associated gear assemblies, and compatibility with seal materials.

TOTAL ACID NUMBER (TAN) - using ASTM D 664, the quantity of base, expressed in milligrams of potassium hydroxide, that is required to neutralize all acidic constituents present in one gram of sample. See neutralization number.

TOTAL BASE NUMBER (TBN) - using ASTM D 2896, the quantity of perchloric acid, expressed in terms of the equivalent number of milligrams of potassium hydroxide that is required to neutralize all basic constituents present in one gram of sample. Also, using ASTM D 664 with hydrochloric acid. See neutralization number.

TRIBOLOGY - science of interactions between surfaces moving relative to each other. Such interactions usually involve the interplay of two primary factors: the load, or force, perpendicular to the surfaces, and the frictional force that impedes movement. Tribological research on friction reduction has important energy conservation applications, since friction increases energy consumption. See friction.

TWO-STROKE CYCLE - see internal combustion engine.