Minnesota Boiler License Practice Exam

On a closed system, why must there be a drain line on the expansion or compression tank?

1. So that any extra air can be evacuated from the system

2. So that if the expansion or compression tank becomes waterlogged, there is a way of draining them

3. A drain line is not required on a closed hot water system

4. To prevent overpressure conditions

The correct answer is: So that if the expansion or compression tank becomes waterlogged, there is a way of draining them

A drain line on the expansion or compression tank is necessary to allow for the removal of excess water when the tank becomes waterlogged. In closed systems, when the air cushion within the expansion tank diminishes due to water absorption, the tank can fill with water, losing its intended function of absorbing pressure fluctuations. If not addressed, a waterlogged tank can lead to inefficiencies in the system and potential failure to maintain the necessary pressure balance. Having a drain line provides a simple and efficient method to release excess water, restoring the tank's function and helping to maintain the system's overall effectiveness. The option indicating that a drain line is not required does not account for the practicalities of system maintenance and performance. Additionally, while evacuating air is important in closed systems, this is typically managed through air vents rather than a drain line. Finally, while it's essential to prevent overpressure conditions, the direct function of the drain line is more focused on managing the waterlogged condition than on pressure management alone.