What type of device is used to control the gas supply to an appliance and is responsive to various conditions?

Prepare for the Master Mechanical License Test with flashcards and multiple-choice questions. Each question includes hints and detailed explanations. Get confident for your exam!

The correct answer is a limit control. Limit controls are critical components in heating systems and other gas appliances. They function to monitor specific conditions, such as temperature or pressure, and can turn the gas supply on or off based on these measurements. For example, in a furnace, a limit control will prevent the appliance from operating if it detects a temperature that exceeds safe operating limits, ensuring safety and efficiency.

Limit controls are designed to respond to various conditions, making them essential for maintaining the correct operational parameters of an appliance. They serve as a safeguard against overheating or other potentially hazardous situations.

In contrast, an electrical relay typically functions as a switch that opens or closes a circuit in response to an electrical signal but does not directly monitor conditions like temperature or pressure. A pressure switch does monitor pressure, but it is specific to that parameter and does not handle other conditions such as temperature. Electronic ignition controls are designed to initiate the ignition process within gas-fired appliances, but they do not control the gas supply in response to varied conditions like a limit control does.

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