smart textiles are fibrous assemblies capable of sensing environmental stimuli and show the desired responds. The use of smarts in applications such medical, military, environmental, and sport is rather common. These textiles can also be used as sensors. The aim of this study is to introduce and develop a new and easy method for controlling of flow and estimation of deformation of hydraulic circuit equipped by textile based strain sensors. Thus, flexible pipes were used in the hydraulic test circuit were covered with cylindrical braids consisting of conductive yarns. In order to evaluate the performance of the designed smart textiles, the exerted pressure in the hydraulic circuit was varied. The resultant deformation of the conductive yarns used in the braids was employed to study the induced changes in the diameter of the flexible pipe of the hydraulic system. Experiments were conducted using six different conductive yarns. The yarns were different in terms of electrical conductivity and composition. The first group of yarns was composed of polyester/stainless steel staple fiber blend containing 28, 40, and 80 percent stainless steel fibers. The second group of yarn was composed of multifilament sliver coated components. The third group was composed of carbon and stainless steel multifilament. An electrical circuit capable of on-line measurement of electrical properties of the conductive yarns was designed. Changes in the electrical resistance of the conductive yarns due to their deformation as a result of hydraulic pressure were measured. A digital camera was also used to measure the changes in the diameter of the flexible pipe used in the hydraulic system. The experiments were carried out in three separate steps. In the first step 6 of the conductive yarns and two types of flexible pipes having diameters of 11 and 16mm diameter were used to produce 12 experimental samples. Changes in the electrical properties of conductive yarns and the variation of hydraulic pipe diameter at pressure of 2 and 4 bars in intervals of 5 seconds during two different cycle time were evaluated. In the second step, the sensitivity of samples selected in the first step was examined. Samples composed of polyester/stainless steel staple fiber (20/80) and carbon multifilament yarn was tested at pressure of 1 bar in time spans of 3 and 5 seconds. Results established that both samples were capable of exhibiting vivid responds to flow pressure by changing their electrical resistance. It was found that sensitivity of the yarn composed of polyester/stainless steel staple fiber (20/80) in comparison to the other samples was higher. In the third step, in order to be assured of the repeatability of results and sustainability of functionality of selected samples in first step, selected sample were subjected to 7 consecutive tests. Results showed that the electrical properties of the conductive yarns used in smart braids are influenced by the number of experiments conducted on the samples. Key words: Conductive Yarns, Hydraulic Circuit, Electrical Resistance, Diameter Variation, Pressure Variation
