Liquid level gauges report the amount of flow through a pipeline, or the amount of liquid in a container. To accomplish this goal the gauge needs to be vented regularly, and often enough this venting is to the atmosphere. To protect gauges, and the liquid inside of the container, from dust and debris in the air a gravity vent guard is installed.
The simplest level indicator gauge for liquid reservoirs is attached to the container and fills to the same level as the container, but must be subjected to the same pressure as the container to work. Because most reservoirs are not held at pressure or vacuum, both the gauge and container are vented to the atmosphere to equalize the pressure. The problem with venting is that it leaves the liquids open to contamination.
The gravity vent guard was first utilized in a coal burning power plant to prevent fine coal dust suspended in the air from entering the gauge.
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