Papers
Plastic Pipes Conference Association # 2018 Las-Vegas
Ryosuke Nagahisa, Shinichi Katoh
We investigated the possibility of using a greaseless polyethylene (PE) ball valve by applying a coating on it to improve the valve’s robustness. In order to verify the valve’s operability, we performed initial-operating-torque, abrasion, and dust tests on both grease-applied and coatingapplied ball valves. These tests revealed that the coated valve was superior with respect to the greased valve in terms of reduced initial operating torque, residual amount of sand (when sand entered the valve), and operating-torque increase rate.
Polyethylene (PE) ball valves are widely used as materials for buried gas pipes, owing to their excellent durability and flexibility. The PE ball valve has a structure in which a resin ball with rubber seat rings on both sides is accommodated in a PE-made body. However, its operability and sealing performances could deteriorate owing to temperature changes leading to valve expansion/contraction and accumulation of foreign materials in the sliding portion of the valve. Therefore, in order to overcome sticking and adhesion of dust, we investigated the application of coatings without using grease on the sliding portion. This study mainly focused on the influence of the coatings on the opening/closing operating torque. We used a valve with a diameter nominal (DN) of 160 mm (with rubber sealing members), on which grease or coatings were applied. We measured its initial operating torque at -20 [°C], which is the minimum temperature stipulated in the InternationalOrganization-for-Standardization-(ISO) standard, to check for the occurrence of sticking at the initial operation. In addition, in order to verify the resistance to abrasion through valve opening and closing operations, we measured the operating torque until performing 200 cycles of opening and closing operations, which is two times stricter than that in the valve performance guidelines in Japan. Moreover, we performed an experiment with sand entering the sliding portion and repeated the opening/closing operations 100 times to evaluate the resistance against disturbance. We confirmed that the coating-applied valve exhibited a lower initial operating torque at low temperatures than the grease-applied valve. Moreover, in the dust test, we confirmed that not only the adhesion of dust to the valve body, but also the operating-torque increase through repetitive opening/closing operations could be suppressed if grease was not used.
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