3-72 Troubleshooting, Testing, and Maintenance
• Fixing rotor seal leakage
Refer to the figure “Rheodyne 7725i injector: exploded view” on page 3-73 for
each procedure.
Tightening the needle seal
The needle seal, a PTFE sleeve in the rotor seal, may not seal correctly around
a needle that is smaller than average. A poor seal results in a loss of accuracy
in sample loading.
To reform the PTFE sleeve to make a good seal:
1. Remove the needle from the needle port.
2. Push gently on the plastic needle guide with the eraser end of a pencil.
Do not squash the PTFE sleeve. Repeat if necessary.
To check for a proper seal around the needle:
1. Fill the syringe with water. Place the injector in the Load position and
slowly discharge the water in the syringe into the injector. Notice the
lack of resistance to syringe discharge.
2. Repeat step 1 with the injector handle halfway between Load and Inject
(the pump must be off). The resistance to discharging the syringe should
now be much greater.
The needle seal holds only a few psi of pressure, and will not completely
prevent syringe discharge with the handle in the halfway position.
Replacing the position sensing switch
The position sensing switch is a magnetic reed switch actuated by a magnet in
the shaft. The switch sends the inject signal to the controller, signaling the
controller to begin a gradient. If a gradient does not begin after an injection,
replace the switch. The switch is rated for 100 VAC at 200 mA.
To replace the switch:
1. Remove the stator, stator ring, and 60° stop ring.
Caution: Always use the correct type and gauge needle to load the
injector, or damage to the rotor seal can result.
To Next Page
Loading...
