Introduction
to Regulators
| Regulators |
| Regulators are used in
gas systems to reduce the pressure from a high pressure source
to a safe working pressure for use. A pressure regulator should
always be used when positive control of the pressure in a gas
stream is required. A pressure regulator is as much a safety
device as it is an important tool. All MEGS regulators are
cleaned for oxygen service except as noted. |
| Basic
Regulator Types |
|
There are two basic
types of pressure regulators: a single stage type and a dual
stage type. The outward appearance of the two distinctly
different types is somewhat similar and difficult for the novice
to distinguish. Most pressure regulators are fitted with two
gauges to monitor pressures (most line regulators only have
one). Established convention in the United States and Canada has
situated the high pressure gauge connected internally to the
inlet of the regulator on the right side of the regulator when
facing from the front. This gauge is used to monitor the source
pressure. The low pressure gauge connected internally to the
outlet of the regulator is situated on the left side of the
regulator when facing from the front. This gauge is used to
monitor the outlet pressure (this is the only gauge most common
on line regulators).
Usually an outlet
valve is affixed to the outlet port of the regulator. This valve
is to be used to shut the regulator on or off for brief periods
of time. It should never be used to throttle or control the flow
of gas emitted from a regulator. This practice could cause
serious damage to both the regulator and its operator. Flow
should always be controlled by some other piece of equipment
such as a rotameter or mass flowmeter.
DUAL STAGE regulators
reduce the source pressure to outlet pressure in two steps. The
first stage of the regulator reduces the inlet pressure to about
3 times the maximum working pressure. This type of regulator is
highly recommended for services requiring a near constant
delivery pressure as the source pressure decays. Actual outlet
pressure regulation is controlled by the second stage through
the use of the hand knob.
SINGLE STAGE
regulators perform the same function as the two stage regulator
but in a single step down of source to outlet pressure. For this
reason, the outlet pressure cannot be as accurately controlled
as the source pressure decays. We highly recommend that single
stage regulators only be used in circumstances where the
operator can monitor and adjust the regulator as needed or where
the regulator is supplied a nearly constant source pressure.
LINE REGULATORS
are single stage regulators that are used to provide
point-of-use pressure monitoring and control. For example, a lab
may have gas cylinders located in a room on the first floor. The
gas may be piped up to instruments located in a lab on the
second floor. In this case, it is difficult to monitor the gas
pressure directly at the instruments, since the regulators are
located on the cylinders on the first floor. A line regulator
may be installed near the instruments for convenience of
monitoring the delivery pressure at the point of use. These
regulators are installed directly into gas lines, and have a
single delivery pressure gauge.
|
| Gauges |
| Gauges
are used to monitor the pressure within a system. The basic
component of a gauge is a hollow metal tube that expands and
contracts a very exact amount under varying pressures. This tube
is connected to the part of the gauge usually screwed into a
regulator and also connected to a series of gears. The gears are
further connected to a needle, which is what the user sees from
the front of the gauge. |
| MEGS
Regulators |
|
1. GENERAL
PURPOSE—These products are suitable for applications where
cost is an overriding factor. Generally, these products are best
suited to applications involving gases that are less than
99.995% purity level (for pure gases) or unanalyzed mixtures.
Also, these products should not be used when there is a concern
of moisture, air or hydrocarbon contamination to gases.
2. HIGH PURITY—These
products are suitable for applications where maintaining the
purity of a gas or mixture is the overriding concern. Generally,
these products are best suited to applications involving gases
that are greater than 99.995% purity level (for pure gases) or
analyzed mixtures. These products are also highly recommended
when dealing with more hazardous gases that are either
corrosive, toxic or pyrophoric. Typically these products are
used in analytical laboratory or special situations.
3. ULTRA-LINE—Or
Semiconductor Grade, these products are suitable and highly
recommended for applications where the highest obtainable purity
and the least risk of contamination is absolutely necessary.
Typically, this describes all of the applications associated
with the Semiconductor manufacturing industry and also has
applications in the Pharmaceutical and Chemical Processing
industries.
|
| High
Purity Features |
|
The
features of a regulator determine the type of service for which
it can be used. A regulator intended for a high purity
application has different features than a unit designed for
general purpose use. Three main features determine the
suitability of a regulator for high purity applications:
Body
Type: Regulator bodies
may be of forged or barstock construction. Barstock bodies are
used for high purity applications for the following reasons:
- Reduced internal
volumes: Because barstock bodies are machined, it is
possible to achieve a small internal cavity in the regulator
body. The low internal volume makes purging the regulator
easy, allowing for removal of contaminants like moisture and
oxygen.
- Tight grain
structure of the metal: The cold drawing process produces
metal barstock with a very tight grain structure. This tight
grain structure prevents the regulator’s internal surfaces
from adsorbing moisture and contaminants, allowing them to
be purged easily.
- Low Ra surface
finish: The machining process allows for very low Ra
(Roughness Average) surface finishes on the barstock. The
low Ra finish minimizes particle shedding, which contributes
to contamination.
Diaphragm
Material: Diaphragms may
be constructed of elastomers (neoprene, Viton, etc.) or
stainless steel. Stainless steel diaphragms are used in high
purity regulators because they do not adsorb and release (or
"offgas") contaminants. When a regulator is removed
from a cylinder, it is exposed to ambient air. An elastomeric
diaphragm will adsorb moisture and any other contaminants from
the air. When the regulator is put back into service, the
elastomeric diaphragm releases these contaminants, which find
their way back into the system. A stainless steel diaphragm is
unable to adsorb any contaminants, so it does not contribute to
system contamination.
Type
of Seals: The seal
between the body of the regulator and the diaphragm is important
in maintaining purity. A poor seal creates a leakage point
through which contaminants may enter the system. A metal to
metal seal (metal regulator body sealing to a metal diaphragm)
is the most reliable, leak-free type of seal. An elastomeric
diaphragm can degrade over time, compromising the integrity of
this seal.
|
| Helium
Leak Testing |
| A complete Helium Leak
Test involves the monitoring of both the inboard leakage of an
item and the outboard leakage of an item. Inboard leak tests are
performed by drawing an internal vacuum on the equipment (under
test), while surrounding it with helium, then monitoring the
helium leakage rate from the outside to the inside. Outboard
leak tests are performed by pressurizing the subject item with
helium and analyzing the surrounding space for the presence of
helium. Upon completion of the test, a certificate is written
and forwarded with the item to the customer. In the case where
100% of the items are leak tested, a Certificate of Conformance
can be requested for the item. |
| Regulator
Overhaul |
| Many times the useful
life of a regulator can be extended several years by completing
the overhaul procedure. This procedure replaces all of the
internal expendable parts of a regulator with new ones.
Sometimes, though, a regulator is beyond repair. In that case MEGS
Gas Products will inform the user of this condition
upon inspection. |
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