Rheodyne 7125 Operating Instructions

®

1.0 DESCRIPTION

Model 7125 is a six-port sample injection
valve in which the sample is loaded through
a built-in needle port in the front of the valve.
Figure 1 shows the flow diagram of the
valve. The circles represent the ports in the
valve stator. The dark and white grooves
represent the connecting passages in the
rotor seal. The large circle represents the
needle port.
The sample loop is loaded through the
needle port in the LOAD position. Rotation
of the knob 60° switches the valve from
LOAD to INJECT. In INJECT the mobile
phase flows through the loop.

2.0 SUPPLIED WITH THE VALVE

Supplied with the valve in a separate bag
®
are RheFlex fitting sets for all ports and the
items shown below. A 20 µL sample loop is
standard with the valve.
• Hex Keys
• Needle Port Cleaner
• Mounting Screws
• Vent Tubes
The #22 gauge needle supplied in the valve
should be removed from the needle port
before using the valve.

3.0 SPECIFICATIONS

• Maximum Temperature: 80°C
• Maximum Operating Pressure: 48 MPa
(482 bar, 7000 psi)
• Flow Passage Diameters: 0.6 mm (0.024")
and 0.5 mm (0.018")
• Wetted Surfaces: stainless steel, ceramic,
and an inert polymer

4.0 IMPORTANT SAFETY NOTICES

4.1 Warning: When using sample loops
larger than 100 µL, shield yourself from
mobile phase coming out of the needle port
when the valve is turned from INJECT to
LOAD. Example: 1 mL loop ejects 20 µL
upon decompression from 19 MPa (200 bar,
2898 psi).
4.2 Warning: When using the Needle Port
Cleaner, empty the syringe slowly to prevent
solvent from squirting back at you.
4.3 Caution: Rinse the valve with water
after using buffer solutions to prevent
crystals from forming, which can cause
scratches on the rotor seal.
Rheodyne LLC • A Unit of IDEX Corporation • 600 Park Court, Rohnert Park, CA 94928 • (707) 588-2000 • Fax (707) 588-2020

Operating Instructions

Model 7125
Manual Sample Injector
2
Pump
Position A (LOAD)
Fig. 1. Model 7125 flow diagram.

5.0 USING PROPER SYRINGES

Use syringes with #22 gauge syringe needle,
without electro taper and with 90° point style
(square cut). Using the incorrect needle size
will damage the injector.

6.0 INSTALLATION

a) To mount the valve on a panel, remove
the handle by loosening the two handle set
screws. Use the two screws supplied to
fasten the valve to a panel.
b) Replace the handle by tightening the two
set screws on the two flats of the shaft.
c) Connect the two vent tubes (supplied) to
Ports 5 and 6. Place the outlet ends of both at
the same horizontal level as that of the
needle port to avoid siphoning. See Figure 2.
d) Connect the pump to Port 2 and the
column line to Port 3. Leave the column
disconnected from the valve during initial
flushing.

7.0 FLUSHING THE INJECTOR

In INJECT, flush the needle port with 1 mL
of mobile phase, using the Needle Port
Cleaner as shown in Figure 3. At this time,
the pump flushes the loop. See Warning 4.2.

8.0 MAKING AN INJECTION

There are two common methods of loading
the sample loop – complete or partial filling.

8.1 COMPLETE LOOP FILLING

In complete-filling, the volume of sample
Fig. 2. Correct position of vent lines.
injected is set by the volume of the loop (this
includes the valve passages). This method
produces the highest precision.
Overfill the loop with at least two to five
www.rheodyne.com
Waste
6
Waste
1
5
4 Needle Port
3 Pump
Sample Loop
Column
Position B (INJECT)
Fig. 3. Use of Needle Port Cleaner.
loop volumes of sample. Six to ten loop
volumes will provide even better precision.
An excess of sample is needed because
mobile phase near the wall of the loop is
displaced slowly due to the laminar flow
effect shown in Figure 4.
To completely fill the loop:
a) See Warning 4.1 and turn to LOAD.
b) Insert the syringe into the needle port.
You will feel tightness during the last 2-3
mm of travel as the needle passes through the
needle seal and then stops against the stator
face.
c) Load the sample.
d) Leave the syringe in and turn to INJECT.

8.2 PARTIAL LOOP FILLING

If you only have small quantities of sample,
this is the method of choice. In the partial-
filling method the volume of sample injected
Fig. 4. Laminar flow effect.
is set by the syringe. In this method, no more
than half a loop volume of sample should be
loaded into the loop. For example, load no
more than 10 µL into a 20 µL loop. With
larger volumes some of the sample is lost out
Vent Line 6. This is because sample flows
down the center of the loop at twice the
average velocity due to the laminar flow
effect shown in Figure 4.
Waste
6
Waste
1
5
Needle Port
2
4
3
Sample Loop
Column
Needle Guide
Syringe Barrel
Needle Port Cleaner
Handle Assembly
Sample
Mobile Phase
Tube Wall Flow
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