Choosing the Right Bourdon Tube Gauge: Plastic vs. Painted Steel Cases Explained

I. Introduction

II. Understanding the Bourdon Tube Gauge

A. Working Principle

B. Importance of the Case

III. Plastic Case Gauges

A. Characteristics

1. Lightweight
   • Plastic cases are typically much lighter than their painted steel counterparts. This makes them easier to handle and install, especially in applications where the gauge needs to be moved or positioned frequently. For example, in portable testing equipment or in some light-duty industrial settings where ease of maneuverability is a priority, the lightweight nature of the plastic case gauge can be a significant advantage.
2. Corrosion Resistance
   • Many plastics used in gauge cases have good resistance to corrosion. They are not affected by moisture, most common chemicals, and do not rust like metal. This makes plastic case gauges suitable for use in environments where there is a risk of exposure to corrosive substances, such as in chemical laboratories, certain food processing areas, or in outdoor applications where the gauge may be exposed to rain and humidity.
3. Cost-Effective
   • Plastic case gauges are often more cost-effective to produce than those with painted steel cases. This can result in a lower purchase price, making them an attractive option for applications where budget constraints are a factor. However, it’s important to note that the cost savings may not always outweigh the performance differences depending on the specific application requirements.

B. Advantages

1. Electrical Insulation
   • Plastics are generally good electrical insulators. This can be beneficial in applications where there is a risk of electrical interference or where the gauge may come into contact with electrical components. For example, in some electrical power systems testing or in areas where there is a high concentration of electrical equipment, a plastic case gauge can provide an added level of safety by preventing electrical conduction through the case.
2. Impact Resistance
   • Some types of plastic can offer good impact resistance. They can absorb and distribute the force of impacts better than metal, reducing the risk of damage to the internal components of the gauge in case of accidental drops or collisions. This is useful in applications where the gauge may be subject to rough handling or in environments where there is a possibility of objects hitting the gauge, such as in a busy industrial workshop or on a construction site.

C. Considerations

1. Temperature Limitations
   • Plastics have a relatively lower temperature tolerance compared to steel. Most plastic case gauges are suitable for a narrower temperature range. They may start to deform or lose their mechanical properties at higher temperatures, and their accuracy may be affected. In applications where high temperatures are present, such as in some industrial processes or near heat sources, the performance of a plastic case gauge may be compromised. It’s important to ensure that the operating temperature of the application is within the acceptable range of the plastic case material.
2. Chemical Compatibility
   • While plastics are generally resistant to many common chemicals, there are some chemicals that can interact with or degrade certain types of plastics. It’s crucial to verify the chemical compatibility of the plastic case with the substances it may come into contact with in the specific application. For example, in some highly specialized chemical processing plants where exotic chemicals are used, the plastic case may not be suitable if it cannot withstand the chemical environment.
3. Durability in Harsh Environments
   • Although plastic case gauges can be durable in many situations, in extremely harsh environments with high mechanical stress, abrasive particles, or continuous exposure to UV light (if outdoors), the plastic may degrade over time. For example, in a mining operation with a lot of dust and vibration, or in a desert environment with intense sunlight, the plastic case may not have the same long-term durability as a painted steel case. In such cases, the long-term reliability and lifespan of the gauge need to be carefully evaluated.

IV. Painted Steel Case Gauges

A. Characteristics

1. Strength and Durability
   • Painted steel cases are known for their strength and durability. Steel is a robust material that can withstand high mechanical stress, impacts, and vibrations. It provides excellent protection to the internal components of the gauge, ensuring reliable operation even in harsh industrial environments. For example, in heavy machinery manufacturing plants, oil and gas refineries, or in construction equipment where the gauge may be subject to rough handling and harsh operating conditions, the painted steel case can withstand the rigors and protect the gauge.
2. Temperature Resistance
   • Steel has a higher temperature tolerance compared to most plastics. Painted steel case gauges can operate in a wider temperature range without significant deformation or degradation in performance. They can handle higher temperatures, making them suitable for applications where heat is a factor, such as in steam systems, high-temperature industrial processes, or in environments with significant temperature fluctuations. However, the paint coating on the steel may also have its own temperature limitations, and it’s important to ensure that the combined material can withstand the operating temperatures.
3. Aesthetic Appeal
   • Painted steel cases can have a more professional and finished look compared to plastic cases. The paint finish can be customized to match the aesthetic requirements of different applications or to conform to corporate color schemes. This can be important in applications where the appearance of the equipment is a consideration, such as in control rooms, laboratory setups with a specific visual standard, or in some consumer products where the gauge is visible and part of the overall design.

B. Advantages

1. Chemical Resistance (Depending on Paint Type)
   • When coated with the right type of paint, painted steel cases can offer good chemical resistance. The paint can act as a barrier, protecting the steel from corrosion and chemical attack. However, the effectiveness of the chemical resistance depends on the quality of the paint and its compatibility with the chemicals in the environment. Some specialized paints are designed to withstand specific corrosive substances, making the painted steel case gauge suitable for use in chemical processing plants and other environments where chemical exposure is a concern. But it’s important to ensure that the correct paint type is selected for the specific application.
2. Magnetic Shielding (if Steel is Magnetic)
   • Some types of steel are magnetic, and the painted steel case can provide a degree of magnetic shielding. This can be beneficial in applications where there is a need to protect the internal components of the gauge from external magnetic fields. For example, in some electronic manufacturing processes or in areas where there are strong magnetic sources nearby, the magnetic shielding properties of the painted steel case can help ensure the accuracy and stability of the gauge by preventing interference from magnetic fields.

C. Considerations

1. Weight
   • Painted steel cases are generally heavier than plastic cases. This can be a disadvantage in applications where weight is a critical factor, such as in portable or handheld devices where excessive weight may cause operator fatigue or limit mobility. In some installations where the gauge needs to be mounted on a lightweight structure or in a situation where multiple gauges are used and the overall weight needs to be minimized, the heavier weight of the painted steel case may need to be taken into account.
2. Rust and Corrosion (if Paint is Damaged)
   • While the paint on the steel case provides protection against rust and corrosion, if the paint is scratched, chipped, or damaged in any way, the underlying steel is exposed and can start to rust. This can lead to degradation of the case and potentially affect the performance and lifespan of the gauge. In environments where the gauge may be subject to abrasion or mechanical damage that could compromise the paint integrity, such as in a marine environment with saltwater spray or in a manufacturing plant with moving parts that could rub against the gauge, additional measures may be needed to protect the paint or to regularly inspect and maintain the gauge to prevent rust formation.
3. Cost
   • Painted steel case gauges are typically more expensive than plastic case gauges, both in terms of initial purchase cost and sometimes in terms of maintenance. The cost of the steel material itself and the painting process contribute to the higher price. In applications where cost is a major constraint and the performance requirements can be met with a plastic case gauge, the additional expense of a painted steel case may not be justifiable. However, in applications where the durability, temperature resistance, and other features of the painted steel case are essential, the long-term benefits may outweigh the higher initial cost.

V. Application-Specific Considerations

A. Industrial Settings

1. Heavy Industry (e.g., Mining, Metalworking, Oil and Gas)
   • In heavy industry applications where there are high mechanical stresses, extreme temperatures, and exposure to harsh chemicals and abrasive materials, painted steel case gauges are often the preferred choice. Their strength, durability, and temperature and chemical resistance can withstand the demanding conditions. For example, in an oil rig, the gauge needs to be able to handle the vibrations from the drilling operations, the high pressure and temperature of the oil and gas, and the corrosive nature of the substances involved. A painted steel case gauge with appropriate chemical-resistant paint and a high-temperature rating would be more suitable in this case than a plastic case gauge.
2. Light Industry and General Manufacturing
   • In light industry and some general manufacturing processes where the environment is less harsh but still requires a reliable and accurate gauge, either plastic or painted steel case gauges could be considered depending on specific factors. If the application involves some exposure to chemicals or moisture and weight is not a major issue, a plastic case gauge with good chemical resistance could be a cost-effective option. However, if there is a need for a more durable and aesthetically pleasing gauge that can handle a wider range of temperatures and occasional impacts, a painted steel case gauge may be more appropriate. For example, in a food processing plant where the gauge may be exposed to some cleaning agents and water, but the temperature and mechanical stress are relatively moderate, a plastic case gauge may be sufficient. But in a precision manufacturing process where the equipment looks and durability are important, a painted steel case gauge might be preferred.

B. Laboratory and Research Environments

1. Chemical Laboratories
   • In chemical laboratories, both plastic and painted steel case gauges may be used depending on the specific chemicals being handled and the experimental conditions. If the chemicals are relatively mild and the focus is on cost and ease of use, a plastic case gauge with known chemical compatibility could be suitable. However, for more aggressive chemicals or where there is a need for a more durable and accurate gauge that can withstand a wider range of laboratory conditions, a painted steel case gauge with appropriate chemical-resistant paint may be a better choice. For example, in a research laboratory working with highly corrosive acids, a painted steel case gauge with a specialized coating would be more reliable in protecting the gauge and ensuring accurate pressure measurements over time.
2. Physics and Engineering Laboratories
   • In physics and engineering laboratories where there may be a need for high accuracy, temperature stability, and resistance to mechanical vibrations, painted steel case gauges are often favored. Their stability and durability can provide more reliable measurements in experiments involving precise pressure control. However, in some cases where the gauge needs to be integrated into a lightweight experimental setup or where electrical insulation is a priority (to avoid interference with sensitive electrical measurements), a plastic case gauge may be considered if it can meet the required accuracy and temperature limits. For example, in a low-temperature physics experiment where the gauge needs to be insulated and lightweight, a plastic case gauge with suitable low-temperature performance could be an option, but if the experiment also requires high mechanical stability and accuracy, a painted steel case gauge may be more suitable after considering insulation measures.

C. Outdoor and Harsh Environmental Applications

1. Construction Sites
   • On construction sites, where the gauges may be exposed to dust, impacts, and varying weather conditions, the durability and strength of a painted steel case gauge are beneficial. It can withstand the rough handling and the elements better than a plastic case gauge. However, if the gauge needs to be frequently moved around and weight is a concern, a more lightweight plastic case gauge with good impact resistance may be considered, but it should be carefully evaluated for its ability to withstand the dusty and sometimes harsh outdoor environment. For example, a pressure gauge used to monitor the pressure in construction equipment hydraulic systems may be better off as a painted steel case gauge for its durability, but if it’s a portable gauge used by workers for quick checks and needs to be carried around easily, a plastic case gauge with appropriate protection measures could be an alternative.
2. Marine and Coastal Environments
   • In marine and coastal environments, where there is exposure to saltwater, humidity, and corrosive elements, a painted steel case gauge with a good marine-grade paint or coating is often necessary. The saltwater can quickly corrode unprotected metals, and the humidity can affect the performance of the gauge. While some plastic case gauges may offer some resistance to moisture, the mechanical stress from waves and the need for a more durable and corrosion-resistant option usually make the painted steel case gauge a better choice. However, if the gauge is used in a less critical application on a small boat or in a relatively protected area of a marina, and cost is a significant factor, a plastic case gauge with appropriate corrosion-resistant additives in the plastic material could be evaluated, but it should be monitored closely for any signs of degradation. For example, a pressure gauge used on a large ship’s engine cooling system would likely require a painted steel case gauge with a high-quality marine coating, while a gauge used to measure the air pressure in a small sailboat’s cockpit may be able to use a plastic case gauge if it meets the necessary performance and corrosion resistance requirements.

VI. Maintenance and Long-Term Performance

A. Plastic Case Gauge Maintenance

1. Cleaning
   • Plastic case gauges can usually be cleaned with a mild detergent and a soft cloth. It’s important to avoid using abrasive cleaners that could scratch the plastic surface and potentially affect its appearance and integrity. Regular cleaning can help remove dirt, dust, and any contaminants that may have accumulated on the case, ensuring clear visibility of the dial and maintaining the overall functionality of the gauge.
2. Protection from UV Light (if applicable)
   • If the plastic case gauge is used in an outdoor or an environment with significant exposure to ultraviolet (UV) light, it may be necessary to provide some protection. Some plastics can degrade over time due to UV exposure, becoming brittle or discolored. Using a UV-resistant cover or coating (if available) can help extend the lifespan of the plastic case. Additionally, minimizing the direct exposure of the gauge to sunlight when not in use can also be beneficial.
3. Checking for Chemical Damage
   • Periodically inspect the plastic case for any signs of chemical damage, such as swelling, cracking, or discoloration. If the gauge is used in a chemical environment, it’s important to ensure that the plastic is still compatible with the chemicals and has not been affected. If any chemical damage is detected, the gauge may need to be replaced or evaluated for further use depending on the extent of the damage and its impact on the accuracy and safety of the measurement.

B. Painted Steel Case Gauge Maintenance

1. Paint Inspection and Maintenance
   • Regularly inspect the paint on the steel case for any signs of damage, such as scratches, chips, or peeling. If the paint is damaged, it should be repaired as soon as possible to prevent rust formation. Small scratches can often be touched up with the appropriate paint, while larger areas of damage may require more extensive repainting. It’s also important to ensure that the paint used for touch-ups or repainting is compatible with the original paint and provides similar protection against corrosion and environmental factors.
2. Rust Prevention
   • In addition to maintaining the paint integrity, measures to prevent rust should be taken. If the gauge is exposed to a humid environment or substances that can promote rust formation, consider using a rust inhibitor or a protective coating on the exposed metal parts (such as the edges or connections) that may not be fully covered by the paint. Regularly wiping down the gauge with a dry cloth to remove moisture can also help prevent rust.
3. Mechanical Integrity Check
   • Check the mechanical integrity of the steel case and the mounting components. Ensure that there are no signs of deformation, loose connections, or other mechanical issues that could affect the accuracy and stability of the gauge. If the gauge is subject to vibrations or impacts, periodically check for any signs of damage or misalignment. Any mechanical problems should be addressed promptly to maintain the reliable operation of the gauge.

VII. Conclusion