Pressure gauges play a vital role in the operations of various manufacturing industries, offering valuable insights into processes and serving as an early warning system for potential issues. From detecting pressure spikes that could indicate blockages to identifying pressure drops signaling leaks, these instruments are essential.
Many mechanical pressure gauges share the same fundamental components — including a flexible measuring element known as a Bourdon tube. So the challenge is selecting the right gauge for your specific needs. Seeking guidance from experts is a smart initial step in this decision-making process.
Ashcroft is a trusted name in pressure measurement instrumentation with a rich history that dates back to 1852. In this article, you will discover what sets Ashcroft pressure gauges apart and why they are a preferred choice for customers across different industry sectors. You will also get access to additional resources and information that will help deepen your knowledge about how these instruments work. What makes Ashcroft a pressure gauge authority?
Company founder, Edward Ashcroft, was a visionary who acquired the rights to the groundbreaking Bourdon tube pressure sensing system from the French engineer, Eugene Bourdon in 1852. This made Ashcroft the first U.S. manufacturer to produce and distribute pressure gauges in the U.S. using this revolutionary design and resulted in Ashcroft instruments becoming a staple in the engine rooms of locomotives and steamships for decades to follow.
Today, the Bourdon tube is still the most commonly applied measuring element in mechanical pressure gauges for high-pressure applications. However, there are now different styles of Bourdon tubes, multiple manufacturers, and various ways to construct the element.
Bourdon tubes styles:
- C-Tube. Named for its C shape, this style of tube flexes when pressure is applied and is typically used for pressure ranges between 15 psi and 600 psi.
Figure 1. Ashcroft® C-Tube.
- Helical tubes. This type of tube is designed for higher pressure ranges, starting at 800 psi to 30,000 psi. For 50,000 psi to 100,000 psi, Inconel Helical tubes are used.
Figure 2: Ashcroft® Helical Tube.
Types of Bourdon tube construction.
Depending on the specifications of your application, you may need a special kind of Bourdon tube construction. Before you select which is right for you, keep in mind that the construction of this element can impact the life of the gauge. If the construction is not suitable for your application, the gauge can fail and damage your entire operation.
Bourdon tube construction examples:
Seamless. Involves heating a billet until it's white-hot and then shaping it into a 2- to 3-inch diameter "tube shell" through extrusion or piercing. This shell is carefully refined to the desired size by repeatedly drawing and annealing it. Each step of this method can introduce defects and result in uneven tubing.
Welded and drawn. This starts by forming strips into a round tube and welding them together under inert gas. The tube undergoes several drawing and annealing steps to blend the weld with the original metal. The strip material usually has fewer defects compared to tubing, and both sides of the strip can be inspected before it's formed into a tube.
Ashcroft's patented as-welded construction. Ashcroft pressure gauges primarily use the company's patented as-welded construction to ensure the weld is in the tube's lowest stress point, enhancing control over the tube's wall thickness. This approach results in tubes that have a longer and more consistent lifespan.
Similar to the welded and drawn construction, the as-welded tubing starts as an annealed strip but does not undergo additional processes. Instead, the tubing is directly crafted into the finalized Bourdon tube, and the weld is strategically placed on the least stressed flat area, rather than the edges.
Figure 3: Ashcroft Bourdon tube construction.
Rupture, proof and overpressure of Ashcroft® Bourdon tubes
Ashcroft pressure gauges are meticulously designed to uphold precision and pressure boundary integrity, even in the face of challenging conditions like vibration and pulsation in the field. Our customers often ask about our pressure gauges' rupture (burst) pressures, overpressures and proof pressures. Our answers are based on the ASME B40.100 Bourdon tube rating definitions as follows:
- Rupture Pressure/Burst Pressure: This is the maximum pressure at which the pressure assembly may no longer contain pressure.
- Proof Pressure: The maximum pressure that a gauge can endure without any change in accuracy. This can be expressed as a pressure value or as a percentage of the full scale.
- Overpressure: The application of pressure beyond the full scale.
Ashcroft proof pressures
- Gauges with a dial size of 4½" and larger, with open or solid front cases. Proof pressures per ASME B40.100 (excluding retard and differential pressure gauges) with ranges up to 1000 psi have a proof pressure of 130% of the span.
- Gauges with ranges above 1000 psi to 15,000 psi. Proof pressures are 110% of the span and increase by an extra 20% if the overload stop option is chosen.
- Industrial gauges like the 2½", 3½" Ashcroft®1009S, and 63mm Ashcroft® 1008S, with ranges up to 600 psi. Proof pressures are 125% of the span. For ranges exceeding 600 psi, the proof pressures are 110% of the span.
- Gauges with a diameter of 100 mm and larger, open or solid front Bourdon tube pressure gauges. Per EN 837-1, proof pressures are 130% of the span. When an overload stop is specified, the proof pressures are increased to 150% of the span.
Note: Pressure gauges must not operate continuously at the proof pressure limits specified. The maximum continuous pressure a gauge should endure is 75% of the gauge span as per ASME B40.100.
Ashcroft rupture pressures
Refer to Figure 4 below for the rupture pressures concerning 2 ½" and 3 ½" dials in industrial pressure ranges, and Figure 5 for the rupture pressures related to process gauges with a dial size of 4 ½" and larger pressure gauges.
Figure 4: Rupture pressures in PSI per ASME B40.100 for 2½”, 3½” 1009, 63mm and 100mm 1008s pressure gauges.
Figure 5. Rupture pressures in PSI Per ASME B40.100 for 4½” and larger pressure gauges rupture pressure.
Ready to learn more about pressure gauges?
Now that you know how Ashcroft introduced Bourdon tube pressure gauges to the U.S. market and have a better understanding of the different styles and construction types of these sensing elements, you may have more questions about choosing a pressure gauge for your specific needs. If you find that you have more questions, please contact one of our industry experts who will be happy to assist you.
If you want to explore further insights on choosing the right pressure gauge, we think these articles may be of interest to you:
- Seven Steps to Select a Pressure Guide
- 6 Reasons Pressure Gauges Fail Instrument Audits
- How Does Temperature Affect Pressure Gauge Performance?
In the meantime, download our Avoid Pressure Equipment Failure guide.
