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Comments
When
the syringe is inserted, the needle travels along the needle port tube
for about 4.5 cm before it reaches the needle seal. During this time the
friction is low. Then the tip of the needle enters the needle seal and
travels another 3 mm, during which time the friction is higher. The needle
is stopped by contact with the ceramic stator face.
Failure of the needle seal is more likely when vent tube #6 is plugged by buffer salt crystals. Check that tube if you suspect Cause A.
Leakage out the needle port will occur when using the wrong syringe. When the needle is too short the tip will not reach the needle seal. When the needle is too small in diameter the seal will not grip it tightly enough. The needle should be 0.7 mm OD (#22 gauge) x 5.1 cm (2 in) long and 90° point style (square-cut end). The Model 3725 requires a .062 - .065 mm OD needle x 5.1 cm (2 in).
Do not use a beveled, pointed, or tapered needle.
It is normal for fluid to pass from the port as the needle is inserted. It displaces fluid left in the port after flushing.
Leakage out the needle port during loading will cause non-reproducible analytical results. See Symptom #7.
Rheodyne RheBuild™ Kits are available for all injectors. Kits contain only genuine Rheodyne parts together with tools and instructions.
Symptom #1
Fluid leaks out the needle port only while loading the loop, i.e. while depressing the plunger of the syringe (see Fig. 3).Slowly insert the syringe needle all the way into the needle port and notice the friction:
- If friction
increases slightly during the last 3 mm of travel, and the needle then
comes to a hard stop, see Cause A.
- If the friction does not increase, the needle does not penetrate the needle port as far as previously, and the stop seems somewhat soft, see Cause B.
Fig. 3. Sample leaking out the needle port while loading sample.
Cause A
The needle is penetrating the needle seal (see Fig. 4), but the seal is not gripping tightly enough to prevent leakage around the needle. Some or all of the sample flows back into the needle port tube and out the needle port. See comments.Solution
Push in on the plastic needle guide with the eraser tip of a pencil (see Fig. 5). This pushes on the needle port tube, which compresses the needle seal, reducing the hole diameter.
Fig. 4. Detailed view of the needle seal (located in the rotor seal) sealing around needle.
Fig. 5. To reform the needle seal, push the eraser end of a pencil against the needle port.
Cause B
The needle is not penetrating through the hole in the needle seal. The diameter of the hole has decreased due to cold flow of the Teflon®. Most or all of the sample flows back into the needle port tube and out the needle port.
Solution
Remove the rotor seal from the injector and use the needle of your syringe (22# gauge) to increase the diameter of the hole by pushing the needle through it. Important - Do not do this with a Model 3725. Replace the rotor seal if the needle seal is damaged beyond repair (see Comments).
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