Water bag pipe
In temperature and pressure measurement sump siphons are often used as additional safety medium. The functioning of this component protects the instrument in the measuring circuit from excessive overload. On the one hand, the siphon tube prevents the “direct” contact of a, for example, very hot medium with the measuring device. On the other hand, the tube can also safely trap and dampen a potentially strong pulsation of the medium. Also, the recurring pressure surges due to comparatively abrupt switching operations in a measuring system are thus effectively reduced.
As a further positive effect, the siphons are also used as a cooling section for highly heated media such as gases or liquids. When exposed to media that is too high-tempered, condensate can form in the pipe as a result of cooling and protect the measuring device from damage. This protection also results in a prolonged life of the entire measuring system. Before commissioning a measuring system constructed in this way, however, it is absolutely necessary to perform or ensure filling of the siphon with a special cooling barrier liquid.
Materials and applications
Water bag pipes are available in various designs. Here you will find the so-called U-shape and the circular shape execution. Both forms are manufactured according to DIN 16282. The U-shape is usually used for horizontal pressure extraction. The somewhat more difficult vertical pressure extraction can be done with the circular shape design. The circular shape has also proven to be “commercially available” in the market and is referred to as a standard design. The installation of a siphon tube is usually on the obturator or optionally also on the pressure gauge itself.
The two types are also available in different materials. As a standard siphon the material steel (eg St 35.7 / P235 GH) is offered. High-quality sack tubes then also have an alloy of chrome / nickel steel (eg CrNi 1.4571). As a special design siphons can also in the material Monel (65% nickel, 33% copper and 2% iron) are related, which is particularly tensile and thus suitable for high pressures. This special material originally comes from turbine engineering for ship technology.
For water bag pipes, limited operating temperatures and operating pressures also apply with regard to the material used. For the material steel a maximum of 160 bar at up to 120 ° C, 120 bar at up to 300 ° C and 100 bar at up to 400 ° C apply. For chrome-nickel steel, slightly higher operating pressures apply as follows: 160 bar at up to 120 ° C, 140 bar at up to 300 ° C, and 130 bar at up to 400 ° C. These values are to be regarded as absolute operating limits. With standard siphon tubes, the maximum operating pressure is even limited to 25 bar.