flow rate and pressure issues

[bal]

Hi to everyone,

I have noticed something strange with two hp 5890 devices. The first is the type hp 5890a and the second is hp5890 series ii. Both they work with packed columns. In the first gc the inlet pressure of the column is adjusted to value in order to yield the desired flow at the column exit (measured at room temp) and this pressure value remains constant at a wide temperature range. In the second device the inlet pressure is also adjusted at room temperature but it incerases as the temperature of the oven is increasing. From the software of both devices neither the pressures nor the flow rates can be controlled. Apparently there is a problem with one of the devices...
The answer to my following questions would help:

1. The flow rate appearing in the equation of the Vn is measured at room temperature. I guess this flow rate has to be constant during the measurements at different temperatures. Is that correct?
In this case the gc should be equiped with a flow controller. I also guess the stability of the flow is made by changing the pressure based on the characteristics of the column and the temperature. Another question is if that is possible to made with an hp5890 series ii equiped only with a column head pressure control and a pressure gauge .
2. If the inlet pressure of the column is adjusted then is it normal to see the inlet pressure increassing when the temperature rises or there is maybe an insulation problem or something else?

Thanks in advance

[Peter Apps]

The most likely explanation is that the A series machine has a pressure regulator and that Series II has a mass flow controller. On the series II the inlet pressure increases because the viscosity of the gas increases with temperature.

Peter

[chromatographer1]

I concur.

You should be able to set the second GC to constant pressure instead of constant flow. It is in the software.

best wishes,

Rod