Which device prevents a vacuum from forming in a low-pressure gravity return steam heating system?

In a low-pressure gravity return steam heating system, a vacuum breaker is used to prevent a vacuum from forming within the system. When steam condenses, it can create a vacuum that could impede the flow of equalizing air or make it difficult for water to return to the boiler. A vacuum breaker allows air to enter the system as needed, effectively breaking the vacuum and ensuring that the proper pressure is maintained for efficient operation.

This device is critical in maintaining the balance and functionality of the steam heating system, as it ensures that both steam and condensate can flow freely without the risk of vacuum-related issues, which could lead to system malfunctions.

In contrast, other devices such as a check valve, pump, and heat exchanger serve different purposes within the heating system. A check valve is designed to prevent backflow, a pump is used to move fluids through the system, and a heat exchanger facilitates heat transfer between two fluids. While these devices play important roles in the overall operation of a steam system, they do not specifically address the prevention of vacuum formation as effectively as a vacuum breaker does.