Minnesota Boiler License Practice Exam

To reduce thermal shock on hot water boilers, which devices are typically used?

1. A hot water heater, electric heater, or air preheater

2. Low limit or low fire hold control, 3-way valve, run around pump

3. No devices needed

The correct answer is: Low limit or low fire hold control, 3-way valve, run around pump

To reduce thermal shock on hot water boilers, the effective use of controls and valves is crucial. A low limit or low fire hold control helps maintain the proper water temperature in the system, preventing abrupt changes that could lead to thermal stress. When the water temperature drops below a preset level, the low limit control ensures that the burner operates only at low fire, helping to gradually increase the temperature and thus, minimizing the risk of thermal shock. Additionally, the inclusion of a three-way valve assists in regulating the flow of water and allows for the mixing of cooler water with the hotter water returning from the system, which helps to stabilize the temperature. This mixing action can further mitigate sudden temperature changes within the boiler, enhancing overall safety and equipment longevity. The run-around pump is often used in conjunction with these controls to circulate water between the boiler and heat exchangers in a controlled manner, maintaining a consistent temperature throughout the system. Together, these devices effectively manage water temperature changes and significantly reduce the risk of thermal shock in hot water boilers.