Air elimination

When the piping system is filled with the heat transfer fluid air is pushed out of the pipes as the fluid enters. This air must be removed for proper flow to occur. To remove this air, valved openings in the pipe system are installed at high points. These are called “air vents”; their valves are opened to allow air to escape. Usually a 3/8-in. (9.52 mm) ball valve is used. This is a manual operation and when fluid begins to be released at these high points the valve is closed with the captured air is removed. This air removal exercise must be done not only at the initial fluid fill, but also a short time after operation begins and then on a routine basis thereafter. Gases are released from the fluid as it is heated and trapped air can be moving through the system as bubbles. With a fluid velocity greater than 1.3 ft/second (40cm/second), these gas bubbles will move with the fluid until they reach the air vents in the system and there they can be released. The air vents consist of a short section of an expanded pipe section with a valved pipe outlet placed on the top of the expanded pipe section. The larger pipe volume allows the gas to collect without disturbing fluid flow and thus the gases can be removed when the air vent is opened.