Not all gas regulators are created equal
Choosing the best regulator for your application is critical but can be a mine field. The selection can vary based on your application, gas service, required pressure and purity.
High-purity applications require equipment that will help maintain the purity of the system. Many laboratory applications are sensitive to contamination from elements such as moisture, oxygen, and other gaseous vapours that may be present in ambient air. These contaminants enter the system when the regulator is removed from the cylinder during a cylinder changeout, or they may enter through leaks or faulty seals.
Very often, we select the cheapest regulator that fits the cylinder. Selecting an inferior-quality regulator may compromise the outcomes of your analysis. It is important to understand why a laboratory gas regulator can cost more than an industrial or less reputable brand regulator. The key difference is that they are designed for superior stability and longevity during operation. This can be identified by the body construction and material compatibility, diaphragm and seal material.
Many industrial regulators are made from forged brass bodies. This process involves pouring casting metal in a mould under pressure. The resulting product has a more porous grain structure and therefore the internal surfaces tend to adsorb contaminants that eventually find their way into the system. A quality laboratory regulator should be formed by bar stock construction. This involves machining out a solid piece of metal, which is a more expensive process but produces a smoother and cleaner internal surface. This method makes it easier to achieve a smaller internal cavity in the regulator body, allowing for easier purging and removal of contaminants like moisture and oxygen.
The body material is also an important consideration. Unlike industrial application, where brass is a suitable material for most inert gases, material compatibility considerations are necessary in high-purity applications. Stainless steel is more suited to avoid chemical reactions between the regulator body and a reactive gas.
Diaphragm material is one way of identifying if a regulator is built for laboratory applications or for industrial applications. A laboratory regulator uses a stainless steel or Hastelloy diaphragm, whereas an industrial regulator will be using a rubber or EPDM diaphragm. Elastomer materials adsorb and release contaminants. While this material is economical for coarse material applications, it doesn’t offer for high-purity applications.
It is important to select a regulator made by a manufacturer who guarantees no gas can leak in or out of the regulator over a certain period. A laboratory regulator has a typical leak tightness of 1 x 10-8 mbar L/s of helium, whereas an industrial regulator only has a typical leak tightness of 1 x 10-3 mbar L/s of helium. A reputable brand will offer better leak tightness in their regulators. For the safety of the operator, flammable or toxic gas must not be allowed to leak into the environment. A quality regulator with good leak tightness ensures this.
Contrary to most thinking, the misconception is that if there is a small leak in the regulator or anywhere in the pipeline, high-pressure gas from within should leak outwards rather than ambient air leaking inwards. Atmospheric air is a major impurity to ultrahigh-purity gas installations. When there is a constant high-velocity gas flowing through the regulator, atmospheric air can be siphoned into the regulator via venturi effect if the regulator’s leak tightness is weak, resulting in the degradation of the gas purity. A 5.0 grade (99.999%) gas containing only 10 ppm (parts per million) of gas impurities can quickly degrade to as low as 3.0 grade (99.9%) if atmospheric air manages to infiltrate into the gas stream through these tiny leaks.
How do I minimise risk of contamination?
A periodic leak check should be performed to make sure no connecting joints have come loose over time due to regular compression/decompression caused by cylinder changeout, or expansion/contraction caused by seasonal change or cylinder changeout. A pressure drop test measures the leak severity by first pressurising the line to a set pressure and timing how long it takes for the line pressure to drop to zero. Hold the pressure for at least an hour to assess whether there is any concern in leaks.
If you identify a leak, we recommend you contact Coregas to arrange a replacement or for assistance to conduct a detailed leak check to validate the leak tightness of your installation.
What is the recommended practice for gas chromatography?
Some laboratory instruments, the gas chromatograph (GC) being one of them, are sensitive to gas impurities. A cylinder regulator does not have an integrated purge valve. Each time the regulator is disconnected from the cylinder, for example when changing out an empty cylinder, atmospheric air will enter the regulator and the downstream pipeline. When a new cylinder is connected, ultrahigh-purity gas from the cylinder will mix with the atmospheric air inside the regulator, travel down the pipeline and enter the GC. Without a gas trap, the resulting effect is an incorrect reading on the GC. If no purging is done every time a new cylinder is connected, the gas trap’s shelf life will dramatically reduce. Over time, the gas trap will become saturated and will no longer trap any more impurities. If a saturated gas trap is not replaced on time, it will become a source of contaminants. Excessive exposure to high oxygen levels can burn out and damage the column inside the GC, resulting in costly repairs.
A wall-mounted regulator, equipped with purge functionality, prevents atmospheric air from entering the regulator. This feature allows the user to use the ultrahigh-purity gas from the new cylinder to purge out any atmospheric air that may have found its way into the pigtail or flexible hose. Purging during cylinder change out will improve the lifespan of gas traps.
The added benefit of a purge valve mitigates the danger associated with disconnecting a pressurised equipment. The purge valve allows the operator to first vent off the gas pressure before disconnecting the line from the old cylinder.
How to prolong the lifespan of your regulator?
Reputable brand regulators should be a laboratory asset for a lifetime. To ensure you maximise the life of this asset, these are the basic steps to follow:
When connecting a regulator to a new cylinder, the operator must not open the cylinder valve quickly and shock the regulator. Supersonic gas travelling inside the regulator can damage the mechanism and cause the regulator to creep. A damaged regulator will have an uncontrollable outlet pressure that constantly creeps upwards no matter how much adjustment is made to the pressure setting. This phenomenon can be easily identified by a constant gas discharge at the regulator’s pressure relief valve.
It is recommended to always open the cylinder valve slowly and never allow a regulator to vibrate. If vibration is observed, the operator should quickly close the cylinder valve to stop the vibration and prevent the regulator from further damage. Re-open the cylinder valve slowly until the required line pressure is reached. If the vibration continues, the regulator should be replaced with a larger regulator that can cope with a higher flow rate.
Regulators are essential equipment for a laboratory. However, very often they are an afterthought during the laboratory design process and are left to the very last when a gas cylinder needs to be connected to an instrument. It is imperative to select the right gas equipment that will match the performance of a modern and advance laboratory instrument to reduce contamination vulnerabilities.
Coregas offer a range of specialty gas equipment to suit specific laboratory requirements. For specialist advice regarding the right regulator, panel or supply system for your application, get in contact with one of the Coregas experts.
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