Pressure and temperature measurement at extremely low ambient temperatures

Standard pressure gauges and thermometers generally cope with ambient temperatures right down to -40 �C. But what must be the features of a mechanical measuring instrument that works perfectly well in polar climates with even lower temperatures? This could be explained utilizing the WIKA POLARgauge� as an example. This product family has been designed specifically for measurement at extremely low ambient temperatures down to -70 �C. The instruments are mainly utilized in crude oil and gas processing; for example, in the local pressure and temperature tabs on pumping stations and pipelines.
Minus 40 �C ? this value is often exceeded faster than one thinks. This is demonstrated with a turn to Russia. There, tables with standard temperature values even indicate more than -60 �C for some regions. For mechanical instruments which will be operated such ambient conditions, two critical points should be observed:
For pressure measurement at extremely low ambient temperatures only available with filled case: The WIKA pressure gauge model PG23LT.
1. The case filling
A measurement at extremely low ambient temperatures requires filled-filled measuring instruments. The liquids used for this protect the instrument from condensation formation within the case caused by temperature fluctuations. They thus prevent the window from frosting, so that the measured value can be read safely.
However, nearly all silicone oils used for this purpose begin to solidify at temperatures below -40 �C. The movement then no more works, or can even freeze. Application-aligned monitoring of the parameters (e.g. process pressure) can no longer be ensured.
Therefore, for the POLARgauge� series a special low-temperature silicone oil has been specified. This oil remains in circumstances that allows correct measurement and measured value display, even at -70 �C.
The case of the POLARgauge� model PG23LT (r.) compared to a typical version (l.): It has no elastomers.
2. The elastomers
Elastomers are found in every mechanical pressure gauges or thermometers. They offer a secure sealing between the individual components. In Heartbreaking , they are the flat gasket at the window, and with pressure gauges additionally the blow-out device on the trunk of the case and the vent valve for pressure compensation.
However, the sealing materials used in standard designs cannot durably withstand suprisingly low ambient temperatures. They become brittle over time and lose their sealing properties. This results in the case filling escaping. This, subsequently, leads to the formation of condensation and the frosting of the window.
Therefore, in the development of the POLARgauge� series, elastomers have already been eliminated in all critical points. The seal between the window and case is constructed of a special material. It really is adapted to extremely low ambient temperatures. The vent valve has a stainless steel cap.
Overview of the WIKA POLARgauge� series
Note
You can get more info on the POLARgauge� series on the WIKA website via the following links. The product family currently comprises four instrument types: The Bourdon tube pressure gauge model PG23LT, the differential pressure gauge models 733.51, 733.31 (filled versions of the models 732.51, 732.31), the bimetal thermometer model 55 and the gas-actuated thermometer model 73. Thus, a suitable variant is available for every application. Do you want to buy differential pressure gauge models? Inside our WIKA online-shop you will find some of our standard designs. For those who have any more questions, your contact will gladly assist you to.

Leave a Comment