1. Pre-Installation Considerations

Material Compatibility
One of the first things to consider is the compatibility of the materials used in both the flow meter and the piping. Oxygen is a highly reactive gas, and improper materials can lead to oxidation, contamination, or even combustion. For oxygen systems, only materials that are cleaned for oxygen service should be used. In oxygen systems, certain metals are considered burn-resistant alloys when used within defined process conditions, such as oxygen purity, temperature, and material thickness, at or below a specified exemption pressure. Examples of highly burn-resistant metals include copper, nickel, and copper/nickel alloys like Monel®. Other engineering alloys, such as stainless steel, can also offer varying levels of burn resistance. However, their performance depends on factors like oxygen pressure, purity, temperature, equipment configuration, piping layout, and the thickness of the metal.

Local Legislation and Certification
Before installation, it’s critical to review and comply with local legislation regarding oxygen systems and pressure equipment. In the European Union, for instance, compliance with the Pressure Equipment Directive (PED) is mandatory for systems operating above 0.5 bar . Additionally, only certified technicians with proper training in oxygen handling should be allowed to install and maintain the system. Certification in oxygen safety and handling is vital to ensure compliance with both legal requirements and safety protocols.

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2. Installation Location

Avoiding Flow Disturbances
The accuracy of a thermal mass flow meter is highly sensitive to flow disturbances. For optimal performance, the meter should be installed in a straight section of the pipeline, away from elbows, valves, or any other components that could cause turbulence. As a general rule, aim for 10-15 pipe diameters of straight pipe upstream of the meter and at least 5 diameters downstream. At VPInstruments we advice to take at least 20 pipe diameters, when available.

Accessibility
Ensure that the flow meter is installed in an easily accessible location for future calibration, inspection, and maintenance. Proper access helps minimize downtime when the system requires servicing and ensures that technicians can easily follow maintenance protocols.

3. Measuring and Operating Conditions

Temperature and Pressure Stability
Thermal mass flow meters are designed to measure gas flow based on heat transfer principles, making them sensitive to rapid temperature changes. The installation point should be in an area where temperature is stable, or slowly varying, and within the meter’s operational range. Unstable conditions could lead to measurement errors and exceeding the specifications my even damage to the flow meter.

Dry Gas Environment
Oxygen systems should be as free from moisture as possible. Condensation can interfere with the thermal flow meter’s ability to provide accurate readings. If moisture is present, consider installing air dryers or other filtration systems to ensure the gas remains dry.

4. Safety Considerations

Ventilation and Fire Safety
Since oxygen supports combustion, it’s crucial to ensure good ventilation around the flow meter installation area. In the event of a gas leak, a well-ventilated environment can prevent the buildup of oxygen, reducing the risk of fire. Additionally, it’s essential to adhere to fire safety regulations, such as maintaining appropriate distances from potential ignition sources.

Oxygen Cleanliness
All components of the system must be cleaned and prepared for oxygen service. This includes degreasing all parts to remove any traces of oil or grease, as these contaminants could ignite in the presence of high-purity oxygen. Proper cleaning protocols are vital for preventing potentially catastrophic accidents.

5. Calibration and Maintenance

Calibration for Oxygen Applications
The thermal properties of Air and Oxygen are nearly identical, so they do not have a large impact on the sensor accuracy. This is why at VPInstruments we calibrate our flow meters with air.

Regular Maintenance and Inspections
To ensure long-term accuracy and safety, routine maintenance is essential. Regular visual inspections should be conducted to check for signs of wear or contamination. Additionally, the system should undergo periodic recalibration, as required by both the manufacturer’s specifications and local regulations .

6. Local Compliance and Certified Technicians

Installing a thermal mass flow meter in an oxygen system is not a simple task. It requires certified technicians who are trained in oxygen safety procedures and are knowledgeable about the specific risks associated with oxygen systems. Many regions have stringent local regulations governing the installation of oxygen systems, including certifications for those working on such equipment. Compliance with these regulations is non-negotiable.

Check Local Legislation
Different countries and regions have their own set of regulations regarding the installation and operation of oxygen systems. In the European Union, for instance, the PED (Pressure Equipment Directive) must be followed . Before starting any installation, consult the relevant local standards and legislation to ensure compliance. Failure to do so can result in hefty fines, legal action, or worse—serious safety hazards.

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