Two Position Injector and Valve Applications
Application guide
Two Position Injector and Valve Applications
These illustrations show basic sample injection techniques using Valco two position valves. With rare exceptions, there is no difference between switching valves and external volume sampling valves, so the same valve can be used for either function.
The unique advantage of 8 and 10 port valves is that they reduce extra column volume by combining sampling and switching functions in a single valve. This minimizes expense, maintenance, service, and risk of leaks as compared to multiple 6 port valve systems.
Explore the flow paths below. Open an application to watch the valve switch positions automatically. Use Pause to study a diagram, or choose Position A or Position B. Reduced-motion preferences start playback paused.
Browse all 18 applications
- Alternate column regeneration10 port
- Backflush of precolumn to vent6 port
- Detector selection from two columns, or one column and auxiliary carrier4 port
- Dual microvolume sample injection6 port
- Heart cut trapped in a loop and injected onto a second column10 port
- Loop sampling with backflush of precolumn to vent10 port
- Loop sampling with backflush to detector8 port
- Loop sampling with two column sequence reversal10 port
- Microvolume sample injection4 port
- Same sample to different loops8 port
- Sample enrichment (cleanup) using dual precolumns10 port
- Sample injection6 port
- Sample injection and heart cut to detector10 port
- Simultaneous injection of the same sample onto two separate columns10 port
- Simultaneous injection of the same sample onto three separate columns14 port
- Two column selection6 port
- Two different samples to same column10 port
- Two different samples to two columns12 port
Alternate column regeneration
10 port
When columns must be regenerated following each analysis, this technique permits automation of the process. While one column performs the analysis, the second column undergoes regeneration by use of an auxiliary pump. Once the first analysis is complete, the valve is switched and the regenerated column is now ready for analytical use.
Backflush of precolumn to vent
6 port
This plumbing scheme allows slower eluting components (end cut) which are not of interest to be backflushed to vent. Often a shorter version of the analytical column is used as the precolumn.
Once all components of interest have entered the main column (at port 2), the valve is switched, backflushing the precolumn to vent and reducing analysis time. An auxiliary source of carrier or mobile phase is required for this application
Detector selection from two columns, or one column and auxiliary carrier
4 port
This unique configuration allows analysis of different parts of one analysis with two different detectors, without splitting or multiple injections. For example, fixed gases can be analyzed with a thermal conductivity detector, followed by the analysis of a hydrocarbon fraction with a flame ionization detector.
Dual microvolume sample injection
6 port
The CI6 injector shown in this application is not on this website. Please contact us for details.
This microvolume injector can be used to alternate between two different samples. Each time the valve is switched, a sample is injected.
When the two sample inlets are connected in series, the valve injects the sample each time the valve switches. This is particularly useful in heavy duty cycle operations to minimize valve wear.
When the sample/waste and pump/column connections are swapped, the valve can be used to inject the same sample onto two different columns, in alternation.
Heart cut trapped in a loop and injected onto a second column
10 port
Sample is injected (using a separate injector) onto an analytical column. Early eluting components (front cut) pass through a trapping loop and are detected at port 3. The valve is then switched, and the center (or heart cut), which was retained in the trapping loop, is injected onto the second column to the detector (at port 4).
Late eluting components (end cut) are trapped on the first column. When the valve is switched again, the end cut passes through the trapping loop to the first detector, completing the analysis.
Loop sampling with backflush of precolumn to vent
10 port
When components of interest are low boiling, this plumbing scheme allows "heavy" components with long retention times to be backflushed to waste. After the sample loop is loaded in Position A, the valve is switched to Position B to inject the sample onto column 1. As soon as all components of interest have entered column 2, the valve is switched back to Position A. Column 1 is backflushed to vent during the analysis, reducing the total analysis time.
Loop sampling with backflush to detector
8 port
One valve performs the functions of sampling and backflush valves, simplifying operation and reducing cost. When components of interest are detected, the strongly retained components are backflushed and removed from the column, without temperature programming.
Loop sampling with two column sequence reversal
10 port
This is ideal for fixed gas-from-CO2 analysis where no "high boilers" are present. Column 1 is packed with a porous polymer and Column 2 with molecular sieve. The sample loop is loaded in Position A. When the valve is switched, the loop contents are sent onto Column 1.
As the inorganic gases and methane leave Column 1 and enter Column 2, the valve is returned to Position A, reversing the column sequence. CO2 now leaves Column 1, becoming the first peak. The inorganics and methane are separated by the mole sieve and pass through the porous polymer column to the detector.
Microvolume sample injection
4 port
The internal sample (fixed volume) flowpath is used when very small volumes are required. The sample size is determined by a passage engraved on the valve rotor, allowing precise, repeatable injections.
In Position A, the sample flows through the sample passage while the mobile phase flows through to the column. The third passage is inactive. In Position B, the sample passage is in line with the column and the mobile phase injects the contents of the sample passage onto the column. The passage which was inactive in Position A allows the sample to continue flowing without interruption.
Same sample to different loops
8 port
In a dual external sample loop configuration, sample is injected in both positions. In Position A, Loop 2 is loaded while the mobile phase flows through Loop 1 and onto the column. In Position B, the Loop 2 sample is injected onto the column and another sample is loaded into Loop 1. When the valve is returned to Position A, the Loop 1 sample is injected onto the column and Loop 2 is reloaded.
Sample enrichment (cleanup) using dual precolumns
10 port
Sample is injected by a separate injector onto one of two precolumns (stripper). Early eluting components vent at port 6 while components of interest are retained on the stripper. When the valve is switched, a new injection is made onto the second stripper while components retained on the first stripper are backflushed onto the analytical column at port 9. This method requires an auxiliary pump at port 4.
Sample injection
6 port
With the valve in Position A, sample flows through the external loop while the carrier flows directly through to the chromatographic column. When the valve is switched to Position B, the sample contained in the sample loop and valve flow passage is injected onto the column.
Sample injection and heart cut to detector
10 port
The sample loop is loaded in Position A. When the valve is switched, the contents of the loop are injected onto the analytical column. The front cut elutes from the column and goes to vent at port 5. The valve is then switched back to Position A, and the heart cut is backflushed to the detector). Once the heart cut has eluted, the valve is switched back to Position B, sending the end cut to waste.
By delaying the switching times, the front and heart cuts could go to waste, with the end cut going to the detector.
Simultaneous injection of the same sample onto two separate columns
10 port
In Position A, sample fills the two loops in series. In Position B, the sample is simultaneously injected into two separate flow systems. A single autosampler used with this flowpath can automate two analytical procedures for the same sample.
In an important non-chromatographic application, the roles of carrier and sample are reversed, permitting two different quantities of two different materials to be dispensed together, as in automatic dilution.
Simultaneous injection of the same sample onto three separate columns
14 port
The 14 port valve permits a variety of plumbing arrangements. This one loads the same sample onto three sample loops for injection onto three different columns. This is used primarily by column manufacturers for QA since samples are injected simultaneously. It has also seen use in labs to perform different parts of the same analysis.
Two column selection
6 port
When two different columns are required at frequent intervals at similar oven temperatures, a 6 port valve can provide rapid selection of the one to be used. The column not in use is protected by a blanket of inert mobile phase, and may be rapidly brought to equilibrium when required. (An 8 or 10 port valve is required if flow must be maintained to the non-selected column.)
Two different samples to same column
10 port
A single 10 port valve permits alternate injections from two loops, which may be identical or of different sizes. This technique replaces a 4 port switching valve (used as the sample selector) and a 6 port sample injector.
In Position A, Loop 2 is loaded with sample 2 while the mobile phase flows through Loop 1 and onto the column. In Position B, the Loop 2 sample is injected onto the column and Loop 1 is loaded with sample 1. When the valve is returned to Position A, the Loop 1 sample is injected onto the column and Loop 2 is reloaded with sample 2.
Two different samples to two columns
12 port
This 12 port plumbing arrangement is simply a dual 6 port diagram; while sample 1 is loaded and subsequently injected onto column 1, sample 2 is loaded and injected onto column 2. As with 10 port valves, the 12 port is capable of a wide variety of sample injection and switching applications.
Blank valve templates
Use these blank diagrams to sketch your own valve plumbing.
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