Pressure Measurement
Bourdon tubes, diaphragm seals, pressure transmitters, snubbers, siphons, manifold bleed valves, and accuracy specifications.
- Explain the operating principle of bourdon tube pressure gauges
- Describe pressure transmitter accuracy, dampening, and specifications
- Identify the purpose of diaphragm seals, snubbers, and siphons
- Outline proper manifold valve and bleed valve procedures
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Bourdon Tube Gauges & Mechanical Elements
Bourdon Tube Principle
The bourdon tube is the most common mechanical pressure sensing element. It consists of a curved, hollow tube that straightens when pressure is applied internally. The movement of the tube tip is mechanically linked to a pointer on a dial. A bourdon tube is used to measure pressure - this is a direct exam fact.
The most common shape is the C-type bourdon tube, but spiral and helical configurations exist for higher sensitivity. The material is typically brass, stainless steel, or phosphor bronze depending on the process fluid compatibility.
Other Mechanical Elements
Bellows are accordion-shaped metal chambers that expand or contract with pressure. They are more sensitive than bourdon tubes and are used for low-pressure measurements. Diaphragm elements use a flexible membrane that deflects under pressure, commonly found in differential pressure transmitters.
A bourdon tube measures pressure by straightening under internal pressure. It is the most common mechanical pressure element and a fundamental concept for the Red Seal exam.