Gas cylinder regulators

Figure 7.2 Gas cylinder regulator plus 3-way needle valve outlet Remove the protective cap from the cylinder fitting and ensure that the fitting is clean and dry.

The synthesis gas cylinder should be installed with an instrument-quality forward pressure regulator, since this will control the experimental pressure of the whole unit. The nitrogen cylinder can have an ordinary regulator, because it is used only for flushing the unit. 

The Regulations relating to gas cylinders apply to suppliers, importers, fillers and owners of cylinders from 1 January 1991 if ... 

Figure 15.4 shows a procedure for the refilling of returnable containers with a chemical of assured quality. (This will require some combination of documentation, sampling and analysis to ensure that the chemical is of the correct type, and in the intended condition.) This is applicable to drums and plastic containers, and bottles, but some modifications are necessary for pressure systems, i.e. gas cylinders, covered by the Pressure Systems Safety Regulations 2000 including ... 

Air from a cylinder at pressures up to about 10 bar (150 psi) is applied to a gas piston that has a relatively large surface area. The gas piston is attached to a hydraulic piston that has a smaller surface area. The pressure applied to the liquid = gas pressure x area of gas piston/area of hydraulic piston. With 10 bar inlet pressure and a 50 1 area ratio, the hydraulic pressure obtained is 500 bar (7500 psi). On the drive stroke, the outlet valve on the pump head is open to the column and the inlet valve closed to the mobile phase reservoir. At the end of the drive stroke, the air in the chamber is vented and air enters on the other side of the gas piston to start the return stroke. On the return stroke the outlet valve closes, the inlet valve opens and the pump head refills with mobile phase. The pump can be started and stopped by operation of a valve fitted between the cylinder regulator and the pump. 

All precautions relating to compressed gas cylinders must be enforced—the cylinders must be secured to an immovable object, such as a wall they must have approved pressure regulators in place they must be transported on approved carts etc. Tubing and connectors must be free of gas leaks. There must be an independently vented fume hood in place over the flame to take care of toxic combustion products. Volatile flammable organic solvents and their vapors, such as ether and acetone, must not be present in the lab when the flame is lit. 

Apparent near the bench on which the GC unit sits are pressure-regulated compressed gas cylinders of hydrogen and air (in addition to the carrier gas, helium or nitrogen). Metal tubing, typically ]/8-in. diameter, connect the cylinders to the detector. A needle valve is used for flow control. These valves are located in the instrument for easy access and control by the operator. 

A typical post-mix unit is shown schematically in Figure 13.3. Water is supplied via a pressure reducer and non-return valves to a carbonator. If the water quality requires it, particulates can be removed by fitting a cartridge filter and chlorine can be removed with a carbon filter. The carbonator is pressurised to a regulated level with carbon dioxide from a gas cylinder. 

Steere, N. V. Ed., 1971, Handbook of Laboratory Safety, The Chemical Rubber Co. Press, Cleveland. Contains a chapter on compressed gas cylinders and cylinder regulators. 

DOT stands for the U.S. Department of Transportation, the agency that regulates the transport and specification of gas cylinders in the U.S. The next entry, for example, 3AA, is the specification for the type and material of the cylinder. The most common cylinders are 3A, 3AA, 3AX, 3AAX, 3T, and 3AL. All but the last refer to steel cylinders, while 3AL refers to aluminum. The individual specifications differ mainly in chemical composition of the steel and the gases that are approved for containment and transport. 3T deals with large bundles of tube trailer cylinders. The next entry in this field is the service pressure, in psig. 

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