At Mid-West Instrument, we design and manufacture precision differential pressure gauges, transmitters, and switches. One of the most common and reliable designs used in mechanical pressure measurement is the Bourdon tube. Bourdon tube gauges are based on the principle that a curved, flattened tube straightens slightly when pressurized, then returns to its original shape when pressure is released. These gauges are versatile, durable, and do not require an external power source, making them a dependable choice across industries. Different types of Bourdon tube are built in several forms, each designed to meet different ranges of pressure and application requirements. Our Model 109 is one example of a Bourdon tube gauge, engineered with high accuracy, durability, and over-range protection, built to deliver dependable performance in demanding environments.
C-Type Bourdon Tube
The C-type Bourdon tube is the most widely used form of this technology. It consists of a C-shaped, flattened, hollow tube fixed at one end and free at the other. When pressure is applied internally, the oval cross-section tends to become circular, causing the tube to straighten slightly. The free end of the tube deflects in proportion to the pressure applied. This movement is then transferred mechanically to a pointer, allowing for pressure indication on a dial.
In practical use, C-type Bourdon tubes are effective for measuring gauge pressures between 0.6 bar (9 psi or 60 kPa) and 60 bar (900 psi or 6000 kPa). For pressures below this range, they may not provide enough deflection to be precise. For pressures above 60 bar, the deflection may not be sufficient, requiring modifications or different tube forms. Still, the C-type remains a standard across industries such as oil and gas, chemical processing, and manufacturing, where straightforward pressure indication is required. The fundamental operating concept is based on Hooke’s Law, with deflection proportional to the applied force within the elastic limit of the tube material.
Spiral Bourdon Tube
The spiral Bourdon tube is a modification of the C-type design, in which the tube is wound into multiple spiral turns rather than a single C-shaped arc. This configuration allows the deflection of each arc section to accumulate into a greater total displacement at the free end of the spiral. The increased motion provides higher sensitivity and more visible pointer movement, especially useful for lower pressure ranges.
Spiral Bourdon tubes are typically used where relatively low pressures must be measured with greater accuracy or sensitivity. The large rotational displacement achieved at the tip of the spiral improves readability and enables more precise scaling on the gauge dial. This makes spiral tubes useful in laboratory instruments, low-pressure process monitoring, and applications where fine distinctions in lower pressure readings are critical. The underlying measurement principle is the same as the C-type, but the extended spiral geometry allows for greater deflection amplification.
Helical Bourdon Tube
The helical Bourdon tube takes the principle one step further by winding the flattened tube into a helix rather than a single curve or spiral. The helical tube can provide a large degree of tip movement within a compact design. A central shaft runs along the axis of the helix, mechanically linked to the free end of the tube. As pressure causes the tube to uncoil slightly, the movement is transferred to the shaft, which converts it into circular pointer motion.
Helical Bourdon tubes are advantageous when high sensitivity and large-scale displacement are required in limited space. They are capable of handling higher pressure ranges than spiral tubes while still providing amplified motion for precise readings. Helical tubes are often found in industrial gauges used for higher pressures or where compact gauge designs are required. Their geometry allows greater efficiency in converting internal tube strain into measurable motion, making them highly versatile for many industrial applications.
Applications and Use of Bourdon Tubes
Bourdon tubes, regardless of their type, are used to measure pressures from as low as 0.6 bar up to as high as 7000 bar (105,000 psi). They are especially useful in industrial environments because they operate purely mechanically without the need for electrical power. Their primary purpose is to provide operators with a real-time visual indication of system pressure, helping prevent dangerous pressure fluctuations or equipment failures.
C-type tubes are widely used for mid-range pressures in industries such as oil and gas, water treatment, and chemical processing. Spiral tubes are more common in lower-pressure applications requiring greater movement and precision. Helical tubes, due to their geometry, are used in high-pressure applications while still providing clear pointer motion and compact designs. Across industries, Bourdon tube gauges play a vital role in flow measurement, hydraulic monitoring, pump testing, and filtration system evaluation.
At Mid-West Instrument, our Bourdon tube designs, including the Model 109, are built with rugged construction, corrosion resistance, over-range protection, and precision accuracy to ensure reliable operation in demanding environments. These gauges are used for applications ranging from hydraulic filter monitoring to pump performance testing and heat exchanger evaluation, all while delivering precise differential pressure readings without reliance on external power sources.
Find the Differential Pressure Gauge Right For You
At Mid-West Instrument, we design Bourdon tube gauges to meet the diverse needs of industrial applications. The three primary types, C-type, spiral, and helical, are each suited for different ranges of pressure and sensitivity requirements, from low-pressure laboratory environments to high-pressure industrial systems. The fundamental operating principle remains the same across all types, a flattened metal tube straightens under pressure and returns to its shape when the pressure is released. Bourdon tube gauges are valued for their reliability, mechanical simplicity, and wide pressure range coverage.
Our Model 109 exemplifies the benefits of a precision-engineered Bourdon tube gauge, offering accuracy, durability, and versatility across a wide range of uses. With over 60 years of experience, we continue to provide reliable differential pressure solutions designed to meet the challenges of today’s industrial environments. Contact Mid-West Instrument to learn more about how our Bourdon tube gauges can support your operations.