Page 243 - Praxair - Specialty Gases and Equipment Reference Guide

Regulators

How to Select Praxair Regulators

Most specialty gases are supplied in cylinders compressed
to high pressures. Pressure regulators reduce these high
pressures to lower pressures that can be safely used in an
operating system. Proper regulator selection is critical for both
safety and effectiveness of operating systems.
Many variables are involved in selecting the proper pressure
regulator. While certainly not a comprehensive list, the
following provides some of the more important considerations.
To further assist in making proper regulator selections, refer to
Section B, Pure Gases or Section C, Mixtures as applicable,
of the Praxair Specialty Gases & Equipment reference guide
for recommendations.

1 Materials Compatibility 5 Output Pressure Range
Materials used to construct regulators must be compatible Regulators must be able to reduce pressure to levels
with the gas – especially those materials (wetted parts) in compatible with the operating system and consistent with
contact with the gas. We offer a wide variety of regulators with process needs. Our extensive offering of pressure regulators
various materials of construction to help ensure that the correct provides numerous choices with delivery pressure ranges
regulator is available for your needs. A materials compatibility available as low as 0-0.5 psig, or as high as 0-6000 psig.
chart is located on pages G •423 - G •425.
6 Inlet Pressure Rating
2 Toxicity Regulators must be able to safely handle incoming gas
Regulators must be designed with vent connectors to permit pressure. Here again, a wide selection is available which
the attachment of a vent line or disposal system as a precaution, includes regulators that handle inlet pressures up to
in the unlikely event of a diaphragm failure. 10,000 psig.

3 Gas Purity 7 Helium Leak Integrity
Like all system components, regulators should be selected to Helium leak integrity is a measure of how well a regulator
protect the purity of the service gas. As an example, regulators prevents gases from leaking into or out of a regulator body.
with stainless steel diaphragms are recommended for high purity The measured quantity is expressed as a flow rate such as
applications because they are more “diffusion-resistant” than 1 x 10 scc/sec He (1 billionth of a cc/sec). In this case, a
-9
those with “rubber-type” diaphragms. For low particulate appli- helium leak integrity rating of 1 x 10 would indicate that the
-9
cations, consideration should be given to selecting regulators regulator would leak enough gas to fill a cubic centimeter
with machine welded VCR connections. Optional helium leak every 33 years. If the rating were 1 x 10 the regulator would
®
-3
tests also help to ensure the integrity of regulators. leak enough gas to fill a cubic centimeter in just 17 minutes.
Helium is used as the test gas because it is chemically inert,
4a Line or Cylinder Regulator
Section E – Gas Handling Equipment
Cylinder regulators as their name implies are connected directly it’s easy to detect and it’s an extremely small molecule which
to gas cylinders. Typically offered in both single and two-stage allows it to pass through the smallest leak. The lower the helium
designs, cylinder regulators normally have inlet and delivery leak specification, the better the regulator will be at preventing
pressure gauges. leaks into the atmosphere and minimizing contamination from
Line regulators, on the other hand, are used directly in piping gases outside the regulator body.
systems such as downstream of the manifold or bulk storage 8 Other Considerations
vessel. Because inlet pressure in piping systems is normally Other criteria for consideration include operating temperature,
constant, line regulators are typically single-stage configurations flow requirements, regulatory issues (e.g. medical regulators
with delivery pressure gauges only. meeting FDA regulatory standards), special applications,
design preferences and cost. Call your local representative
4b Single or Dual Stage Design for further assistance.
Single stage regulators reduce pressure in one step as gas is
consumed. Dual stage regulators are actually two regulators Note:
housed in one body. The first regulator (first stage) is non- Regulators are designed to control pressure. Generally they
adjustable and reduces in-coming pressure to an intermediate are supplied with gauges that indicate pressure. Regulators
setting (typically 250 to 300 psig). The second stage is adjust- do not measure or control flow unless equipped with devices
able and reduces intermediate pressure to final desired delivery (such as metering valve or flowmeter) specifically designed
pressure. Because the second stage sees only relatively minor for those purposes. Contact your local sales representative to
inlet pressure changes from the first stage, dual stage regulators find out more about Praxair’s new line of flow monitoring and
maintain steady delivery pressure and do not require periodic flow controlling devices.
adjustment. They are well suited for applications where
constant delivery pressure is essential.

E•242 1-877-PRAXAIR www.praxairdirect.com