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Ultrasonic Inspection: Vacuum Systems

Introduction

Vacuum pumps and systems are used by many industries for a wide variety of applications. They are commonly used in the power, refining, pharmaceutical, food, groundwater, and paper industries. A vacuum system is a system that has lower pressure than the atmosphere. The lower pressure is often created by a pump, which removes mass (i.e. air) out of the system. The more mass that is removed, the lower the pressure in the system.

The amount of vacuum pressure can be defined in one of several ways. For instance, the height of a Mercury column is a direct measure of atmospheric pressure. The atmosphere at sea level applies a pressure of 14.7 lbs per square inch (psi) and can raise a column of Mercury to 29.9 in. or 760 mm. Any amount of pressure that cannot raise Mercury to a level of 760 mm is referred to as vacuum. 1/760th of an atmosphere is referred to as 1 Torr or the amount of pressure needed to raise Mercury 1 mm. Atmospheric pressure is also referred to as approximately 1 Bar (actually 1.013 Bar). If used as a starting point, as the level of vacuum increases, the measurement becomes smaller. Therefore, 90% vacuum (90% of the mass has been removed) is represented as 100 mbar, 99% vacuum is 10 mbar, and so forth.

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