Question

Draw and describe construction and working of Bourdon tube.

Answer 1

Construction and working : C type bourdon tube is made up of an elliptically flattened tube bent in such a way as to produce the ‘C’ shape as shown in the figure. One end (free end) of this tube is closed or sealed and the other end (fixed end) opened for the pressure to enter. The free end connected to the pointer with the help of geared sector and pinion. Calibrated scale and pointer is provided to indicate the pressure. The cross section view of ‘C’ type bourdon tube under normal condition and pressurized condition is as shown in figure. The pressure which is to be measured is applied to the bourdon tube through open end. When this pressure enters the tube, the tube tends to straighten out proportional to applied pressure. This causes the movement of the free end and the displacement of this end is given to the pointer through mechanical linkage i.e. geared sector and pinion. The pointer moves on the calibrated scale in terms of pressure. The relationship between the displacement of the free end and the applied pressure in nonlinear.

OR

Helical Tube

Construction and working : Figure shows helical type bourdon tube. It is similar to spiral element, except it is wound in the form of helix. The displacement of the tip of a helical element is larger than the spiral element. Central shaft is installed (not shown in fig.) within a helical element and the pointer is driven by this shaft using connecting links. This mechanism transmits only the circular motion of the tip to the pointer which is directly proportional to the applied pressure.

OR

Twisted Tube 

Construction and working : Twisted bourdon tube element is as shown in figure. One end of the tube is fixed and other end is free for application of the twist. As we apply the pressure at the free end, it gives rotation or creates the twist at that end. As we remove the pressure the free end try to retain its original position.

OR

Spiral Tube

Construction and working : Spiral type bourdon tube is as shown in figure. Spiral tubes are made by winding several turns of the tube with its flattened cross section in the form of spiral. When the pressure to be measured is applied to the spiral, it tends to uncoil producing relatively long movement of the tip whose displacement can be indication of applied pressure. Accuracy of this element is higher than ‘C’ type element.