GC035 Controls

Two-stage regulator is connected to the cylinder as a first flow control system, which reduces the tank pressure of up to 2500 psig (psi gauge, or above the atmospheric pressure), down to a level useable level of 20-100 psig. The system should include a filter to prevent particulate matter from entering the regulator and a safety valve. The first valve indicates the pressure in the gas cylinder. With the second valve, one can increase the pressure delivered to the GC. The second stage regulator works better at pressures at least 20 psi higher than the maximum inlet pressure on the GC.

Constant pressure is sufficient to provide a constant flow rate for isothermal operations if the pressure drop in the column is constant. In temperature-programmed operations, the flow rate decreases at constant temperature as a consequence of an increased viscosity of the gas at higher temperatures. Differential flow controllers are used to ensure a constant mass flow rate.

Modern research-grad capillary GCs can be operated at both constant pressure or constant flow. The first one maintains constant head pressure throughout the temperature programmed run, and the flow rate decreases as temperature increases. On the other hand, constant flow mode increases the head pressure as the temperature increases, thus the drop in viscosity by the increase in temperature is compensated and the flow kept constant. In both modes, the flow to the column is also maintained constant when the splitter is opened or closed through the electronic solenoid valve. An electronic pressure control (EPC) is used to detect decreasing flow and increase the head pressure, hence providing a constant flow rate.

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