Gas chromatograph sample and column-switching valve

Details Gas chromatograph sample and column-switching valve Gas chromatograph sample and column-switching valve

1999-01-07

2002-09-24

Williams, Hezron (Department: 2856)

Measuring and testing

Gas analysis

Gas chromatography

C137S863000, C137S869000, C137S885000, C251S061100, C251S062000

Reexamination Certificate

active

06453725

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to valves used in gas chromatographs (“GC”) and more particularly to such a valve that internally blocks fluid communication between ports.
DESCRIPTION OF THE PRIOR ART
All process GCs include a sample valve. The function of such a valve is to collect a precise volume of a liquid or vapor sample. The components of the collected sample are then separated by the one or more columns in the GC based on some physical or chemical property. The one or more detectors inside the GC are used to sense the separated components as they leave the end of the one or more columns so that component concentrations can be determined.
Referring to
FIG. 1
there is shown a simplified block diagram of an on-line process GC
10
. GC
10
has a sample extraction and conditioning system
12
which is used to remove a sample from process stream
14
. The sample is conditioned to filter contaminants out of the sample before it enters sample valve
16
through sample input port
16
a
. The valve
16
has also has a sample output port
16
b
for returning the sample to the sampling and conditioning system
12
and a port
16
c
for injection of carrier gas. A fixed volume of the sample mixture is injected into the flowing carrier gas stream through port
16
a
to start the analysis cycle. The function of sample valve
16
is to trap a constant volume of sample in a sample loop
16
d
and periodically inject the sample into the flowing carrier gas.
The chromatograph column
18
includes a packing, not shown, which may be either a fixed bed of tiny liquid coated particles, tiny porous particles, or the coating on the wall of a capillary tube. The packing is known as the stationary phase and its function is to separate the chemicals in the sample based on some physical or chemical property. The carrier gas sweeps or carries the sample through or past the stationary phase.
GC
10
includes a measuring detector
20
which is located at the outlet of column
18
and produces a signal proportional to the concentration of each component band passing through the detector. GC
10
also includes a reference detector
22
which is exposed to pure carrier gas. Detectors
20
and
22
are connected to vents
21
and
23
, respectively. The electrical signals from detectors
20
and
22
are connected to chromatograph controller
24
. Controller
24
amplifies, digitizes and integrates the raw electrical signal from detector
20
and produces an output signal when detector
20
is exposed to components leaving the end of column
18
while the reference detector
22
is exposed to nothing but pure carrier gas.
As can be seen from
FIG. 1
, sample valve
16
, column
18
, and detectors
20
and
22
are contained in the oven
26
of GC
10
. Oven
26
includes a heater
28
. The oven ensures that high boiling point liquid samples are vaporized in the sampling valve
16
and also keeps components from condensing.
In addition to being used as sample valves, chromatograph valves are also used as column switching valves. A column switching valve is used to redirect the carrier gas flow during an analysis cycle to load specific components onto different columns for further separation. Column switching valves are also used to reverse the flow of carrier gas through a column and backflush components not of interest off the column to a vent.
Prior art sample and column switching valves usually includes a multiplicity of ports but do not provide internal blocking of fluid communication between one or more pairs of ports. Two examples of such valves are the four port double diaphragm model
44
valve and six port double diaphragm model
46
valve both of which are sold by Applied Automation, Inc. of Bartlesville, Okla. It is desirable to preserve the full functionality of all of the ports in the valve. It is also desirable in a GC to conserve carrier gas.
In many applications where a prior art valve is used, carrier gas should not flow out of a particular port or ports when the valve is in one of its two operating modes but should flow out of that port or ports when the valve is in the other of its operating modes. Blocking the port or ports would not accomplish that result as the port or ports are then blocked for both operating modes. Therefore, prior art valves have included additional hardware external to the valve to regulate the flow out of that port or ports. Such regulated flow is however a waste of carrier gas in that valve operating mode where carrier gas should not flow out of the port or ports.
As was described above, the sample valve along with the column and the detectors are inside of the oven in the GC. The GC oven is of a predetermined size and if external hardware is added to the sample valve to regulate the flow out of a port or ports that external hardware must also reside in the oven. Therefore, the addition of external hardware to the sample valve reduces the room in the oven for additional columns and detectors.
SUMMARY OF THE INVENTION
A valve having at least four ports. The valve has first and second operating modes. When the valve is in the first operating mode the at least four ports become at least two pairs of adjacent ports in fluid communication with each other internal to the valve and at least two pairs of adjacent ports not in fluid communication with each other internal to the valve. At least one pair of the at least two adjacent port pairs not in fluid communication with each other internal to the valve when the valve is in the first operating mode separate at least one pair of the at least two port pairs that are in fluid communication with each other internal to valve when the valve is in the first operating mode.
The valve has a first plate which has on its periphery the at least four ports for entry and exit of a first fluid. The at least four ports are in fluid communication with at least four openings in each of the first and second exterior surfaces of the first plate. Each of the at least four openings are associated with a respective one of the at least four ports. The at least four openings in the first exterior surface are blocked when the valve is in the second operating mode.
The valve also has a second plate which has a valve for entry of a second fluid. The second plate also has a first exterior surface which has at least one opening which is in fluid communication with the second plate second fluid entry valve. The valve further has a first diaphragm between the second exterior surface of the first plate and the first exterior surface of the second plate. The first diaphragm pressing against the second plate first exterior surface when the valve is in the second operating mode.
The at least one opening in the first exterior surface of the second plate allows, when the valve is in the second operating mode, fluid communication internal to the valve between all but at least one of the at least two port pairs not in fluid communication with each other internal to the valve when the valve is in the first operating mode.
A process gas chromatograph which has a valve having at least four ports which is embodied as described above, at least one separation column connected to a port of the at least four port valve, and at least one detector connected to the at least one separation column.
A valve having at least 2N ports, where N≧2. The valve also has first and second operating modes. When the valve is in the first operating mode the at least 2N ports become at least N pairs of adjacent ports in fluid communication with each other internal to the valve and at least N pairs of adjacent ports not in fluid communication with each other internal to the valve. At least one pair of the at least N adjacent port pairs not in fluid communication with each other internal to the valve when the valve is in the first operating mode separate at least one pair of the at least N port pairs that are in fluid communication with each other internal to valve when the valve is in the first operating mode.
The valve has a first plate which has on its periphery

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