How Does a 6-Port HPLC Injection Valve Work? Load, Inject and Vent
A 6-port HPLC injection valve switches paired internal passages to move the sample loop between the loading path and the high-pressure analytical path. During loading, the sample-loading mechanism fills the loop. During injection, mobile phase supplied by the HPLC pump passes through the loop and carries the sample into the column.
The high-pressure valve switches flow paths. A complete injection sequence also requires a pump, sample loop, sample-loading mechanism and control program. The following uses the FOREACH HP 2-position, 6-port high-pressure rotary valve with venting to explain these connections.
01How do the six main ports connect the pump, sample loop and column?
Start with an external sample-loop connection example for understanding the principle. The loop is a tube with a known volume, connected to the valve at both ends. The loading mechanism supplies the sample and the HPLC pump supplies mobile phase. The port assignments below are an instructional example; verify actual tubing against the equipment design.
| HP port | Component connected in this example | Function |
|---|---|---|
| 1 | HPLC pump outlet | Supplies mobile phase |
| 6 | Column inlet | Receives mobile phase and the injected sample |
| 2 and 5 | Both ends of the external sample loop | Holds the sample before injection |
| 3 | Sample-loading mechanism | Supplies sample to the valve |
| 4 | Waste path | Collects fluid displaced during loading |
| 7 | Separate vent path | Used with the Vent state |
The essential feature is which ports are connected in pairs at each position. Unlike a rotary selector valve that connects a common port to one of several fluid sources, an injection valve rearranges several connections in one switch to insert or remove the loop from the analytical path.
02Load: fill the sample loop while mobile phase bypasses it
In the HP Load position, connections are 1—6, 2—3 and 4—5. With the tubing above, the HPLC pump supplies mobile phase directly to the column through 1—6; the sample loop is outside that analytical path.
- HPLC pumpMobile phase enters port 1
- Load position1—6 connected
- ColumnSupplied through port 6
A separate path loads the sample. Sample from the loading mechanism enters port 3, passes through port 2 into the loop, and then exits through ports 5 and 4 to waste. This loads the loop while retaining the pump-to-column connection in the Load position of this example.
- Sample-loading mechanismSample enters port 3
- 3—2 pathSample enters the loop
- Sample loopOther end connected to port 5
- 5—4 pathDischarges to waste
Before initial loading, remove air from the path and arrange displacement of previous sample and wash fluid. In full-loop loading, moving one nominal loop volume with the loading mechanism does not prove that the loop is completely filled with the target sample. Confirm sufficient filling by method validation.
03Inject: mobile phase passes through the loop and carries the sample to the column
In the HP Inject position, connections become 1—2, 3—4 and 5—6. Mobile phase from the HPLC pump enters the loop through ports 1 and 2, then reaches the column through 5—6. The sample retained in the loop enters the analytical path with the mobile phase.
- HPLC pumpMobile phase enters port 1
- 1—2 pathConnects the sample loop
- Sample loopMobile phase sweeps out the sample
- 5—6 pathEnters the column
At this point, 3—4 is connected, linking the sample-loading branch to waste. The control program must coordinate loading, valve position and data acquisition, and verify completed switching and sample-transfer time. Sending a valve-switch command alone does not prove that all sample has entered the column.
Injection hold time depends on the loop, connecting tubing, mobile-phase flow rate and analytical method. Switching back too early may impair transfer. The timing between valve actuation and acquisition start must also remain verifiably consistent from cycle to cycle.
04What does venting connect in a 2-position, 6-port valve with venting?
Load and Inject are the HP valve's two main operating flow paths. It also provides a Vent state with the specified connection 3—7. Describe both the two-position, six-port main arrangement and the additional vent function. This does not mean that every six-port valve has a seventh vent port.
- Port 3 branchLoading branch in this example
- Vent state3—7 connected
- Port 7 pathExternal vent or collection path
This does not mean that the entire high-pressure system has been depressurized, nor that the pump-to-column path remains connected during venting. Coordinate the pump, loading mechanism and pressure-release steps according to the complete connections in this state, verifying pressure and fluid destination before operating. Do not vent by loosening a fitting under pressure.
05What do loop volume, valve internal volume and pressure each limit?
| Parameter | Meaning | What cannot be concluded directly |
|---|---|---|
| Sample-loop volume | Establishes nominal sample volume in full-loop injection | A nominal 20 μL loop does not guarantee identical actual injection volume under every loading condition |
| HP internal volume: 0.8 μL | Volume specification for the valve's internal passages | Not the injection volume; excludes the external loop and the complete tubing system |
| HP bore: 0.4 mm | Dimensions of the internal fluid passages | Cannot alone determine system flow, peak shape or analytical results |
| HP maximum operating pressure: 25 MPa | Permitted pressure boundary for this valve | Does not cover every high-pressure or UHPLC condition, and is not a pressure-relief valve setting |
Full-loop injection requires stable, complete loop filling. Partial-loop injection relies more on metering by the loading mechanism, air-gap arrangement and sample distribution in the tubing. The valve cannot automatically detect a full loop or guarantee method injection accuracy by itself.
HP uses 10-32 UNF ports. When selecting fittings and tubing, check thread, sealing geometry, tubing diameter, pressure rating and wetted materials together. Define the complete path's operating boundary using its lowest-rated component and actual pressure fluctuations, rather than the valve rating alone.
06How can loading, injection and cleaning be validated together?
- Under permitted pressure conditions, verify ports and valve positions. Confirm the intended Load, Inject and Vent paths before establishing an automatic sequence.
- Repeat injections of a stable standard sample. Compare peak-area repeatability and differences between the first and subsequent injections; investigate loading volume, bubbles, valve timing and detector stability together.
- Run a blank after a high-concentration sample to check carryover. Optimize cleaning separately for the loading mechanism, valve, sample loop and connecting tubing.
- Observe pressure changes during switching and external leakage. Run full cycles at the target flow rate with the actual fluid and backpressure, then confirm the permitted injection hold time.
These steps establish validation of the equipment and analytical method. One successful valve movement or a passed component check does not establish acceptable system injection repeatability.
07Frequently asked questions
Are six-port injection and six-port selector valves used in the same way?
Not necessarily. An injection valve generally rearranges paired paths to switch the loop between loading and analytical paths. A selector generally connects a common port to one of several candidate ports. Select using each position's connection diagram, rather than counting ports alone.
Does a vent port depressurize the whole HPLC system?
That cannot be inferred. The HP Vent state specifically establishes 3—7. Which parts of the equipment can release pressure depends on other passages and external connections. This is not automatic pressure regulation or a safety pressure-relief valve.
Can the program stay unchanged after installing a larger loop?
Recheck loading volume, displacement and wash volumes, injection hold time and method suitability. With a different loop, the original sequence may no longer fill and transfer sample adequately. Revalidate injection volume and repeatability.