Gas flow switching method and apparatus

Claim 2

Apparatus as claimed in claim 2 in which the controlled pressure is a constant pressure.

Claim 3

Apparatus as claimed in claim 1 in which the means for preventing effluent gas passing from the junction through the remaining limbs comprises means for passing gas at a controlled pressure to them.

Claim 4

Apparatus as claimed in claim 4 in which the same pressure source is used to supply all outlet limbs of the junction.

Claim 5

Apparatus as claimed in claim 5 in which the resistance to gas flow beyond each of the outlet limbs is substantially the same, which comprises a constant pressure source for feeding carrier gas to the column, a let-down valve, and means to feed each outlet limb intermediate the ends thereof with gas from the constant pressure source through the let-down valve.

Claim 6

Apparatus as claimed in claim 5 including a further chromatographic column having an output side connected to an outlet limb and means for feeding gas at substantially the same pressure as that fed to the outlet limbs of the junction to the output side of said further chromatographic column.

Claim 7

A process for controlling a flow of effluent gas stream from a gas chromatographic column whereby the flow of said stream can be switched from one path to another as desired, said process comprising the steps of passing the effluent gas stream through a junction having at least three limbs, one limb being a gas inlet limb for said effluent gas stream and the other limbs being gas outlet limbs, feeding a second gas stream to all outlet limbs other than a first selected one at a point intermediate the ends of said outlet limbs and at a slightly higher pressure than that arising due to the flow of effluent gas stream through the inlet limb and said first selected limb so that flow of said effluent gas stream through said outlet limbs is blocked except for said first selected outlet limb, continuously maintaining the feed of said second gas stream as indicated until the flow of said effluent gas stream is to be switched from said first selected outlet limb to another selected outlet limb, then selecting a different outlet limb according to the path desired for the flow of the effluent gas, discontinuing the flow of said second gas stream to said other selected outlet limb to permit flow of the effluent gas stream therethrough and feeding the second gas stream to said first selected outlet limb to block the flow of said effluent gas stream therethrough.

Claim 8

In a gas chromatographic apparatus, a chromatographic column, a sample source for supply to said column, means for feeding a carrier gas and a sample from said source through said column, means for Discharging effluent gas from said column, and a gas flow switch communicating with said discharge means, said switch comprising a gas flow-through junction having at least three limbs, one limb being a gas inlet limb to receive said effluent gas and two other limbs being gas outlet limbs, means for maintaining a continuous flow of blocking gas at a controlled pressure to a point intermediate the ends of each outlet limb to prevent said effluent gas from passing therethrough except when an outlet limb is selected for such passage, and means operatively associated with each outlet limb for selectively discontinuing the flow of blocking gas to said selected outlet limb to permit flow of the effluent gas therethrough while maintaining the flow of said blocking gas in said other outlet limb and at least one chromatographic column fed by an outlet limb, any other outlet limb feeding a storage device.