Individual Cylinders

WARNING

CO₂ cylinders can be dangerous if handled improperly

Carbon dioxide in cylinders is partially liquefied under high pressure and contains a great deal of energy. If containment is breached (a break in the line or cylinder) the entire contents will vaporize and quickly expand up to 500 times in volume and create very forceful high velocity gas streams. Cylinders must be properly constrained, and proper tubing used, to avoid damage that could generate projectiles.

Any industrial grade of carbon dioxide is acceptable provided it is supplied in a cylinder without a DIP tube. Drawing off the vapor phase leaves non-volatile contaminants behind in the cylinder. Using cylinders with a DIP tube subjects the chromatograph to contaminants soluble in the dense, liquid layer.

Larger tanks are more convenient in that they require to be changed less frequently. Cylinders can contain up to 35 kg of CO₂. Generally, 4.6 mm columns are run at 3 – 5 mL/min, which is approximately 2.5 – 4 g/min of carbon dioxide. This is equivalent to 150 – 250 g/h; 1.2 – 6 kg/day. Thus, a 15 kg cylinder should last 2.2 to 11 days; a 25 kg cylinder would last 4 to 19 days; and a 35 kg cylinder could last 5.3 to 27 days - all depending on use (3 – 5 mL/min; 8 – 24 h/day). For individual users, particularly new users, the use of cylinders is perfectly acceptable. Larger groups should consider installing a gas delivery system and a bulk storage tank.

Locate the cylinder as close to the instrument as possible. In the past, the cylinders were stored at much higher temperature than the lab temperature, which resulted in vaporization in the supply line coming into the lab. Most SFC pumps cannot condense this vapor and therefore, cannot deliver CO₂. Agilent's SFC control module has a very powerful condenser designed to accept vapor phase CO₂. Nevertheless, it is always advisable to not stress any equipment.

Facilities and safety personnel often wish to store and mount the cylinders outside the lab - sometimes quite far from the intended location of the instrument. They should recognize that the transfer lines can hold large volumes, equivalent to a large fraction of a cylinder, particularly if tubing with large ID is used. Shut-off valves at both ends of a transfer line are not recommended, unless one or both has a pressure relief valve or burst disk.

Be sure the cylinder is properly constrained and cannot tip over. Suitable chains or cylinder straps are required.

Cylinders in the USA and Canada use a CGA 320 cylinder adapter. The filter fitting sticking out the back of the SFC control module contains 1/8 inch nut and ferrule(s), which could be used with the supplied 1.8 m (6 feet) tube, or a longer, user-supplied tube, to connect a cylinder to the SFC control module.

There are at least four different European standards for the connection of carbon dioxide cylinders. They do not appear to change at national borders (some users in one country have different supply connections from other users in the same country). Agilent Technologies recommends that customers in Europe contact their gas supply companies and ask them how to mate the cylinders they supply with an American 1/8 OD supply line. This should require a cylinder connector and a reducing union down to a 1/8 inch compression fitting.

WARNING

Leaks will not be sensed or protected

Carefully check supply cylinders and inlet fittings for leaks. Any leaks present in the supply line and inlet fitting will not be sensed or protected by safety features in the module.

Figure: Figure 3.25

where

O	Power off
I	Power on

WARNING

Improper plumbing can cause leaks

It is imperative to use two wrenches to install the supply fitting in the bulkhead filter (entry connection) on the back of the module. Turning or twisting the bulkhead supply filter could cause failures or leaks in tubing within the module.
All supply fittings need to be thoroughly checked for leaks. Any leaks in the supply fittings can vent the CO₂ supply.

CAUTION

Overtightening the fitting could damage the filter

Use two wrenches when installing the CO₂ supply line to the bulkhead filter (entry connection) on the back of the module. Although the filter is captured and should not rotate, there is a remote possibility that fittings inside the module could be loosened by severe stress on the nut on the supply line. Leakage inside the cabinet requires service by trained personnel.

21-Jun-2025