What is the instrument used to measure draft in boilers?

The instrument commonly used to measure draft in boilers is a manometer. This device is designed to measure pressure differences, which is critical when assessing the draft created by the boiler's combustion process. Draft refers to the movement of air and gases through the boiler system, and it is essential for efficient combustion, ensuring adequate airflow to support the burning fuel and proper venting of exhaust gases.

A manometer specifically provides a visual representation of the pressure differential that can indicate how well the draft is functioning. Sufficient draft ensures that the combustion gases are properly evacuated, preventing them from backing up into the combustion chamber, which could lead to inefficiency or safety hazards.

Other instruments mentioned serve different purposes. A thermometer measures temperature, which, while important in overall boiler operation, does not assess draft. A barometer measures atmospheric pressure, which is not directly related to the draft in the boiler itself. A hydrometer is used to measure the specific gravity or density of liquids, not applicable to measuring draft in gases. Thus, the manometer is the most appropriate tool for monitoring the draft in boiler applications.