Glossary of Terms

Here you will find a glossary of specialised terms commonly used in thermostating and metrology.

V

Vario pump

A pressure pump that can be set on a corresponding menu to the various capacity levels concerning flow rate and discharge pressure. This makes possible optimum adaptation to the corresponding application. The LAUDA Vario pump in the Ecoline has five selectable output steps.

Varioflex pump

Varioflex pump is a new centrifugal pump with a pressure and a suction level driven by the same motor. Its pump output can be optimally adjusted in 8 stages to the bath volumes and size via menu. Thanks to its low energy input into the bath and its special plastic, it is suitable for continuous operation at very high temperatures. It is vibration decoupled, therefore low-noise.

An additional safety advantage is offered by the Varioflex pump's patented low-level protection (DGM). By the pressure/suction pump the bath liquid is conveyed from the pressure level into the circulation, the suction level sucks the liquid back into the thermostats. Like the pressure pump, the pressure/ suction pump can also be used for a closed circuit. Compared to the pressure pump, it has the advantage that the pressure in the external circuit falls from positive values (pressure) to negative values (suction) and is almost zero in the external system. This means that even pressure sensitive glass vessels can be thermostated.

In addition, by using a pressure/suction pump an open external circuit (a bath container with constant level device) can also be connected. This is not possible with only a pressure pump, as this only conveys the liquid into the bath. However, a further suction stage is required for conveying the liquid from the bath back to the thermostat. The Varioflex pump is available as a high power model as a pure pressure pump for special devices with higher baths.

Viscosity

Properties of a substance (in this case: of liquids) to flow and become irreversibly deformed under the influence of a stress. Flow energy is converted into warmth.

Viscosity index (for mineral oil products)

Calculated from the viscosities measured at two different temperatures (40 and 100 °C) according to ISO 2909 and ASTM D 2270. Is a standard for the thermal behaviour of various oils. The higher the viscosity index of an oil is, the less it changes its viscosity at various temperatures.

Viscosity, kinematic

Viscosity refers to the flow behaviour of a liquid that can range from thin to highly viscous. Viscosity depends very largely on temperature. It is a measure of the internal friction between adjacent liquid layers at different velocities. Viscosity affects the characteristics (temperature control, pump output) of a thermostat and is therefore particularly important.

Volumetric expansion

The volume change refers to the increase or decrease of the liquid volume at a certain operating temperature with reference to an initial temperature of 20 °C. The liquid volume to be considered includes both that inside the thermostat itself and also that in the external circulating system.

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