Nylon material tube is extensively used for piping pneumatic circuits in the pneumatics industry. Because of its tight tolerance, the tube works well with push-in and compression fittings. The nylon tube is also used in air brake systems in automobiles. https://www.joinarticles.com/u....sage-of-union-ball-v

Usage of union ball valve
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Usage of union ball valve

A double union ball valve, as the name suggests, has two unions - one on each side.