Short Answer:
A Bourdon tube measures pressure by using a curved, hollow metal tube that tends to straighten when internal pressure increases. The tube is sealed at one end and connected to the pressure source at the other. As the pressure rises inside the tube, it causes the curved tube to try to uncoil or straighten slightly.
This movement is transferred through a mechanical linkage to a pointer on a dial, which shows the corresponding pressure. Bourdon tubes are simple, reliable, and widely used in mechanical pressure gauges for measuring gas or liquid pressure.
Detailed Explanation:
Working of a Bourdon Tube in Pressure Measurement
The Bourdon tube is one of the most common and widely used mechanical pressure-sensing devices. It was invented by Eugène Bourdon in the 19th century. It operates on a simple mechanical principle where the shape of a bent tube changes in response to internal pressure. Bourdon tubes are commonly found in analog pressure gauges used in various industrial, automotive, and domestic applications.
Construction of a Bourdon Tube
- Tube Shape
The Bourdon tube is usually C-shaped, spiral, or helical. It is a thin-walled, hollow, elastic metal tube, flattened in cross-section and bent into a curve. - Fixed and Free Ends
- One end of the tube is fixed and connected to the pressure inlet.
- The other end is sealed and free to move.
- Mechanical Linkage
A gear and pointer mechanism is connected to the free end of the tube. This converts the tube’s movement into a rotational motion, which drives the pointer on a calibrated dial.
Working Principle
- Application of Pressure
When pressure is applied through the fixed end, the fluid (gas or liquid) enters the hollow Bourdon tube. - Tube Deformation
As the internal pressure increases, the curved tube tends to straighten slightly. This happens because the pressure inside is higher than the atmospheric pressure outside, and the tube tries to relieve the stress by expanding outward. - Mechanical Movement
The movement of the free end is small but measurable. This movement is transferred to a gear mechanism, which multiplies the motion and turns a pointer on the dial. - Reading the Pressure
The dial is marked in pressure units (like psi, bar, or Pa), and the pointer shows the corresponding pressure based on how much the tube has moved.
Materials Used
- Common materials include brass, stainless steel, or phosphor bronze, depending on the pressure range and the type of fluid being measured.
- For corrosive or high-pressure applications, special alloys are used.
Applications
- Industrial machinery pressure gauges
- Boilers and steam systems
- Pneumatic and hydraulic systems
- Medical equipment like oxygen tanks
- HVAC systems and water pumps
Advantages
- Simple and mechanical, no power needed
- Reliable and durable under normal conditions
- Works for both gas and liquid pressure
- Available in various pressure ranges
- Cost-effective and easy to maintain
Limitations
- Not suitable for very low pressures
- Sensitive to vibration and shock
- Can suffer from hysteresis and wear over time
- Needs calibration for accurate results
Conclusion
A Bourdon tube measures pressure by converting internal pressure into mechanical movement. The pressure causes the curved metal tube to straighten, and this movement is transferred to a pointer through a linkage mechanism. This method is simple, robust, and commonly used in analog pressure gauges for various industrial and domestic applications. The Bourdon tube continues to be a practical and effective tool for direct pressure measurement.