128
VALVES
SwitchingValves
Switchingvalvesdynamicallyalternatebetweentwofluidpathswithout
manuallydisconnectingplumbing. InChromatography, these valves
canbeused for column switching, backflushing, sampleenrichment,
andother techniques. InDiagnosticor Sequencingapplications, the
switching valvemay alternate flowpaths toenableback flushingor
other fluidic taskswithin the instrument.
Rheodyne
®
switching valves operate between two positions, and
may have 6 or 10 ports on the face of the stator (2/6 or 2/10). The
flow paths connect ports around the circumference of the stator.
The Upchurch Scientific
®
manual switching valves (to 1,000 psi)
describedonpage133havedifferent flowpathgeometryasnoted.
InjectionValves
Rheodyne injection valves are a form of switching valve. Injection
valvescanbeautomatedormanual, and theyaregenerallyutilized in
the two-position, six-port (2/6) configuration and have a sample
loopattached.
Thepurposeofan Injectionvalve is to introduceasampleofasolution
intoaflowingstreamof liquid.SomeSwitchingvalvesbecome Injection
valves by the additionof aSample Loop (adefined lengthof tubing
andfittingsconfigured tomatch theangleof thevalveports).Sample is
loadedandheld in the loopuntil injection is triggered,eithermanually
ormechanically.
Rheodyne injectionvalvesareclassifiedaseitherSingleorDualMode,
andeither Front or Rear-loading, basedonhow theSampleLoopcan
befilled.ASingleMode Injectionvalve requirescompletefillingof the
sample loopand is configured for Rear loading, generally inanauto-
sampleconfiguration.ADualMode Injectionvalveallowseitherpartial
orcompletefillingofthe loop,and introducessamplebysyringethrough
theneedleportbuilt into thevalveshaft.Completefillingof thesample
loop inboththeDualandSingleMode Injectionvalvesprovidesgreater
repeatability injection to injection. (See theApplicationNote,page129
forgreaterdetail onpartial vs. complete loopfilling.)
1
1
6
6
5
5
4
4
3
3
2
2
Flowpathof Two-Position, Six-Port SwitchingValve
Position1
Position2
Flowpathof Two-Position, Ten-Port SwitchingValve
Position1
Position2
1
2
3
4
5 6
7
8
9
10
1
2
3
4
5 6
7
8
9
10
Flowpathof Two-Position, Six-Port InjectionValve
LOAD
6
5
4
3
2
1
Column
Pump
Waste
Sample
INJECT
6
5
4
3
2
1
Column
Pump
Waste
Sample
Valve Functions
