Compression fittings

Therma compression fitting - Adaptable link for the thermocouple

The thermocouple is irreplaceable for temperature measurement in experimental laboratories, research, industry, motor sports, and household appliances. To ensure a secure fit, compression fittings must be reliable as well as a precise fit for the thermocouple and suitable for the measurement environment or the expected measurement temperature. With the compression fitting, the thermocouple can be fixed directly at the measuring point and ensure a long-lasting bond between the thermocouple and the measuring environment without slipping. For the different places as well as applications, you can buy the compression fitting which differ in the material, screw-in thread, clamping taper material as well as diameter to meet your requirements. Due to the variability in materials, some compression mechanisms can form strong bonds with the thermocouple, making it difficult to replace, or are equipped for flexible use. The choice of material can also take into account additional desirable properties such as vibration absorption and behavior under pressure.

The structure and function of the compression fitting

In the process industry, the fittings for thermocouples are used for temperature measurement as well as control. They consist of a body, which at Therma is usually made of stainless steel and is offered in various thread sizes, the clamping cone made of various materials for sealing as well as fixing the temperature sensor, and the union nut, which provides support and compression for the cone. The compression fitting provides a secure and partially sealed connection to the process inlet, and the immersion depth of the thermocouple can be varied on site. The compression fitting is basically reusable, although the clamping ring or clamping cone may have to be replaced depending on the material selected. Two types of compression fitting are available. With the wedge ring fitting, the clamping cone penetrates the sheath of the thermocouple and forms a connection that can hardly be loosened. With the compression fitting, the thermocouple is not firmly connected, but can be replaced at any time.

The classic and robust stainless steel compression fitting

The housing as well as the clamping cone of this type is made of stainless steel which can withstand high temperatures and pressure. It is suitable for probe diameters from 1.0 to 3.2 mm and can have screw-in threads in sizes M6, M8 and M8x1. The advantage of the stainless steel compression fitting is its temperature resistance up to approx. 800 °C and the pressure density up to 140 bar created by the stable connection between the thermocouple and the clamping cone. The disadvantage is that the temperature sensor can only be used in combination with the clamping cone and cannot be used separately or with another compression fitting. However, it is reusable as a whole. It can be used in heating construction, industrial as well as plant construction and exhaust gas measurement and is an indispensable element for the precise mounting of our sheathed thermocouples as well as resistance thermometers.

The properties of the ceramic compression fitting for your thermocouple

The ceramic clamping cone and the stainless steel housing are the ideal choice for processes at high temperatures as well as a vibration-prone measuring environment. As with the stainless steel compression fitting, the fitting can be used for element diameters from 1.0 to 3.2 mm and have external threads from M6 to M8 to M8x1. The ceramic clamping cone is suitable for a high temperature range, but is hardly pressure-tight, as it is only connected to the sheath thermocouple by compression. The strength of the more flexible contact is its excellent ability to absorb vibrations, resulting in a secure bond between the element and its surroundings. The shortcoming of this compression fitting is the required replacement of the clamping cone after use. Nevertheless, the thermocouple can be reused at any time with a different compression fitting or with a new ceramic clamping cone.

The brass compression fitting for particularly thin thermocouples

The brass clamping cone is the all-round talent among compression fittings. It promises a pressure tight, vibration absorbing as well as a temperature resistant connection between thermocouple and measuring environment. The material properties paired with the stainless steel housing are suitable for element diameters from 0.5 to 1.5 mm and offers a choice of M4, M6, M8 as well as M8x1 screw-in threads. The brass compression fitting can withstand temperatures up to 400 °C and pressures up to 60 bar. It exhibits the best clamping behavior with fine sheathed thermocouples and forms a firm connection with the element. Although the stable connection can withstand lower temperatures than the stainless steel compression fitting, it can withstand vibrations. However, the disadvantage is similar to the stainless steel compression fitting, which cannot be separated from the temperature sensor.

The Teflon compression fitting for flexible use

A clamping cone made of Teflon in combination with the stainless steel body is designed for low temperature ranges, but scores with the fast exchange of the thermocouple. The Teflon clamping cone used does not have a fixed connection due to the flexible clamping and is therefore ideal for rapid replacement. It is also recommended to change the clamping cone, otherwise the hold of the thermocouple cannot be guaranteed. The compression fitting provides stability to temperature sensors with diameters from 1.0 to 3.2 mm and can be supplied with M6, M8 and M8x1 screw-in threads. The weakness of the Teflon gland is the maximum temperature of +200 °C, which severely limits its use. Therefore, the compression fitting Teflon is mainly suitable for flexible fastening in the low temperature range.