What type of pressure does a tank designed as 'atmospheric' operate under?

A tank designed as 'atmospheric' operates under normal atmospheric pressure. This means that the internal pressure of the tank is equal to the pressure exerted by the surrounding atmosphere, typically around 14.7 psi at sea level. Such tanks are not designed to withstand significant pressure variations above or below this level, making them suitable for storing liquids or gases that do not require high pressure to remain in a liquid state.

In contrast to tanks under negative pressure or vacuum pressure, which are designed to keep their contents from boiling off or being exposed to outside air at lower than atmospheric pressures, atmospheric tanks are vented to the atmosphere and can equalize with ambient pressure. Similarly, high-pressure tanks are engineered to hold pressures exceeding 1 psi, which is not applicable to atmospheric tanks. Thus, the definition and operation of an atmospheric tank are specifically aligned with the concept of maintaining normal atmospheric pressure.