Standard
cylinder-valve outlet connections have been devised by the Compressed Gas Association
(CGA) to prevent mixing of incompatible gases. The outlet threads used vary in diameter;
some are internal, some are external; some are right-handed, some are left-handed. In
general, right-handed threads are used for non-fuel and water-pumped gases, while
left-handed threads are used for fuel and oil-pump gases. To minimize undesirable
connections, only CGA standard combinations of valves and fittings should be used in
compressed gas installations; the assembly of miscellaneous parts should be avoided. The
threads on cylinder valves, regulators and other fittings should be examined to ensure
they correspond and are undamaged.
Cylinders
should be placed with the valve accessible at all times. The main cylinder valve should be
closed as soon as it is no longer necessary that it be open (i.e., it should never be left
open when the equipment is unattended or not operating). This is necessary not only for
safety when the cylinder is under pressure, but also to prevent the corrosion and
contamination resulting from diffusion of air and moisture into the cylinder after it has
been emptied.
Cylinders
are equipped with either a hand wheel or stem valve. For cylinders equipped with a stem
valve, the valve spindle key should remain on the stem while the cylinder is in service.
Only wrenches or tools provided by the cylinder supplier should be used to open or close a
valve. At no time should pliers be used to open a cylinder valve. Some valves may require
washers; this should be checked before the regulator is fitted.
Cylinder
valves should be opened slowly. Oxygen cylinder valves should be opened all the way. Open
up the oxygen cylinder valve stem just a crack. Once the needle on the high pressure
gauge has stopped, open up the valve all the way. This back-seats the valve.
Oxygen cylinders must have the valve opened up all the way because of the high pressure in
the cylinder. There is a back-seating valve on the oxygen cylinder. This
prevents the high-pressure gas from leaking out through the threaded stem.
When
opening the valve on a cylinder containing an irritating or toxic gas, the user should
position the cylinder with the valve pointing away from them and warn those working
nearby.
Cylinders
containing flammable gases such as hydrogen or acetylene must not be stored in
close proximity to open flames, areas where electrical sparks are generated, or where
other sources of ignition may be present.
Cylinders containing acetylene shall never be stored on their side.
An
open flame shall never be used to detect leaks of flammable gases. Hydrogen flame is
invisible, so "feel" for heat. One common practice is to use a natural bristle
broom to "sweep" the air in front of you. All cylinders containing flammable
gases should be stored in a well-ventilated area.
Oxygen
cylinders, full or empty, shall not be stored in the same vicinity as flammable gases. The
proper storage for oxygen cylinders requires that a minimum of 20 feet be maintained
between flammable gas cylinders and oxygen cylinders or the storage areas be separated, at
a minimum, by a fire wall five feet high with a fire rating of 0.5 hours. Greasy and oily
materials shall never be stored around oxygen; nor should oil or grease be applied to
fittings.
| Regulators are gas specific and not necessarily interchangeable! Always
make sure that the regulator and valve fittings are compatible. |
 |
After
the regulator is attached, the cylinder valve should be opened just enough to indicate
pressure on the regulator gauge (no more than one full turn) and all the connections
checked with a soap solution for leaks. Never use oil or grease on the
regulator of a cylinder valve.
If
there is any question as to the suitability of a regulator for a particular gas, check
with the Environmental Health & Safety Department or call your vendor for advice.
The
following rules should always be followed in regards to piping:
- Copper piping shall not be used for acetylene.
- Plastic piping shall not be used for any portion of a high pressure system.
- Do not use cast iron pipe for chlorine.
- Do not conceal distribution lines where a high concentration of a leaking hazardous gas
can build up and cause an accident.
- Distribution lines and their outlets should be clearly labeled as to the type of gas
contained.
- Piping systems should be inspected for leaks on a regular basis.
- Special attention should be given to fittings as well as possible cracks that may have
developed.
A
cylinder should never be emptied to a pressure lower than 172 kPa (25 psi/in2) (the
residual contents may become contaminated if the valve is left open). When work involving
a compressed gas is completed, the cylinder must be turned off, and if possible, the lines
bled.
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When
the cylinder needs to be removed or is empty, all valves shall be closed, the system bled,
and the regulator removed. The valve cap shall be replaced, the cylinder clearly marked
as "empty," and returned to a storage area for pickup by the supplier. |
Empty
and full cylinders should be stored in separate areas.
Where
the possibility of flow reversal exists, the cylinder discharge lines should be
equipped with approved check valves to prevent inadvertent contamination of cylinders
connected to a closed system. "Sucking back" is particularly troublesome where
gases are used as reactants in a closed system. A cylinder in such a system should be shut
off and removed from the system when the pressure remaining in the cylinder is at least
172 kPa (25 psi/in2). If there is a possibility that the container has been contaminated,
it should be so labeled and returned to the supplier.
Liquid
bulk cylinders may be used in laboratories where a high volume of gas is needed. These
cylinders usually have a number of valves on the top of the cylinder. All valves should be
clearly marked as to their function. These cylinders will also vent their contents when a
preset internal pressure is reached, therefore, they should be stored or placed in service
where there is adequate ventilation.
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Always use
safety glasses (preferably with a face shield) when handling and using compressed gases,
especially when connecting and disconnecting compressed gas regulators and lines. |
All
compressed gas cylinders, including lecture-size cylinders, must be returned to the
supplier when empty or no longer in use.
