Gas Pressure Regulator Selection for Specialty Gases
Materials
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General Gas Use
General purpose regulators commonly have elastomeric diaphragms and are most often used in conjunction with packed valves. These regulators are typically forged brass but may be stainless steel depending on the corrosivity of the gas. Performance is satisfactory where slight contamination or diffusion from an elastomeric diaphragm is not important. Brass regulators with stainless steel diaphragms prevent air diffusion and adsorption of gases on the diaphragm. This is particularly important with low concentration mixtures of hydrocarbons where the trace component may be adsorbed on the elastomeric diaphragm. Regulators with Buna-N or neoprene diaphragms are not suitable for GC analysis that can be affected by the diffusion of atmospheric oxygen through the elastomer diaphragm or the outgassing of monomers and dimers from the elastomer.
High-Purity Gas Service
Specialty gases can be effectively delivered by regulators that are classified as high-purity or ultra-high-purity. High-purity regulators are typically made of brass and have stainless steel diaphragms. Ultra-high-purity regulators are typically constructed of brass or stainless steel bar stock with convoluted stainless steel diaphragms having metal-to-metal sealing without using backup O-Rings. Ultra-high-purity regulators used with highly corrosive gases typically have stainless steel diaphragms mechanically linked to the poppet assembly to provide additional sealing integrity.
A high-purity regulator equipped with a stainless steel diaphragm does not outgas organic materials. It also prevents the diffusion of atmospheric oxygen into the carrier gas whereas Buna-N and neoprene diaphragms are permeable to oxygen.
Operating Delivery Pressure Range
Determining the proper delivery pressure can be confusing. It is important to determine two application requirements: the gas pressure that is needed and the maximum pressure that the system may require (these two pressures may be the same). Then, select the regulator’s delivery pressure ranges so the desired pressures are between 5 and 90% of the regulator’s delivery range. A regulator’s performance is at its best within this range.
Regulator Placement (Cylinder or Line)
Specialty gas regulator applications are divided into two types. The first is where the regulator is fastened to a gas cylinder using a Compressed Gas Association (CGA) fitting. The second application is where a regulator is located in a gas line, providing a means to further reduce the line pressure. A line regulator is identified by having the inlet and outlet opposite of each other with a single gauge in the 12 o’clock position to indicate the reduced pressure.