Gas Cylinder Pressure Regulators

By: Robert F. Wallace, Reporter US Vol 28

New Features and Better Performance from Airgas®


Robert F. Wallace
bob.wallace@sial.com

Introduction

The importance of gas purity to a successful gas chromatography (GC) analyses has been widely understood by chromatographers for years. Because gas purifiers play such a large part in the purification process, the role of the gas regulator is often overlooked. The regulator is often the first component of a gas delivery system and the first opportunity for contaminants to enter the system. Additionally, the design of the regulator must ensure contaminants cannot hide inside the body and emit at an unpredictable time. We have updated our line of gas cylinder pressure regulators with new models from Airgas, a recognized worldwide leader in gas delivery products. All are smaller/ lighter models that include inlet check valves, a feature that significantly increases performance.



Figure 1.Single Stage (above) and Two-Stage Regulators (below)

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A Bar Stock Regulator or a Forged Body Regulator?

There are two basic regulator designs, forged body and bar stock. Forged body regulators have a rough internal surface with a larger internal volume. Bar stock regulators, preferred for most chromatographic applications, are machined with a smoother internal surface and lower internal volume.

Our bar stock regulators, with smooth internal cavities, provide a non-pitted surface, allowing more efficient and direct gas flow. This design eliminates the large cavities and pockets associated with forged body regulators and thus contain minimal internal surfaces to which contaminants can cling. The small internal volume (5% of the internal volume of a forged body regulator) provides a more direct gas flow path through the regulator. As a result, all areas come in contact with the gas stream, so any contaminant that enters the regulator is quickly swept out of the body.

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Single Stage and Two-Stage

Contrary to widespread belief, a gas pressure regulator is not a flow control device. The primary function of the pressure regulator is to reduce the high gas pressure in a cylinder or delivery line to a level that can be used by an instrument or process. A single-stage regulator (Figure 2) reduces the pressure to an intermediate pressure that will be further reduced by a secondary regulator (either an in-line regulator or regulator built into the instrument). Two-stage cylinder regulators (Figure 3) reduce the high pressure from the cylinder to a range that can be accepted by the instrument. The two-stage regulator functions as two, single-stage regulators in series. The first stage reduces the inlet pressure to an internally set intermediate pressure, typically 300-500 psig. The second stage, adjusted by turning the control knob, reduces the immediate pressure to the desired delivery pressure.

Figure 2.Single Stage Gas Flow Path


Figure 3.Two Stage Gas Flow Path

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Which do I Choose?

Which regulator will work best for my application? The following are suggestions based on the need inside the laboratory. The Supelco high purity (HP) and high purity plus (HP+) gas cylinder regulators use a stainless steel diaphragm with a captive PTFE seal. Under most GC conditions, with the exception of the most sensitive applications, this diaphragm will ensure reliable and exceptional gas delivery. For more sensitive applications an ultra high purity (UHP) regulator is recommended. These regulators have a stainless steel diaphragm with a metal-to-metal rather than PTFE seal providing a better seal that will not allow contaminants to diffuse into the internal chamber.

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New Regulator Features

Gas cylinder regulators from Supelco now feature a check valve on the inlet fitting that keeps air from entering the regulator body during cylinder change-out, thus eliminating the need for a long purge time following the installation of a new gas cylinder. At the body outlet of the regulator, a shut-off valve keeps air from entering the system during change-out of the downstream gas purification/management components. There are two types of shut-off valves to choose from; a needle shut-off valve on HP models allows for flow control, whereas a diaphragm shut-off valve in HP+ and UHP models has higher leak integrity. The bonnet of the HP and HP+ are made of nickel-plated zinc, giving the regulator a cosmetically better look than nickel-plated brass. The UHP, which is machined brass, can be used in panel mounting applications. There is a 1/8” male stainless steel Swagelok fitting on the regulator outlet, which is compatible with both copper and stainless steel tubing.

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Conclusion

The gas pressure regulator should be designed to minimize the amount of incoming contaminants and remove them before they enter the chromatographic system. This helps guarantee the highest quality gas, resulting in maximum column life and ultimate performance. With the need of the chromatographer in mind, our newly updated line of gas cylinder pressure regulators provides a quality product for inert gases that will reduce and maintain the pressure from a cylinder to a level that can be used by the system, ensuring safety to both operator and instrument.

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