Preliminary Cleaning of the PD-Series Dryer Element

1. Remove any solids or other visible deposits from the outside of the tubing and from the epoxy header.

   1. Brush or scrub away any solids deposited on sample header.

   2. Wipe off any dust or liquid residues from the tubing and header with a clean soft cloth.

2. Blow clean, dry air through the sample outlet end of the header to remove any entrained particles.

3. To dissolve any salt deposits within the tubing, briefly inject DI water into tubing bundle with syringe or plastic squeeze bottle. Do not immerse the headers of the dryer element in water or excessively wet the tubing inside the headers. Nafion tubing swells when exposed to water. If the tubing inside the epoxy headers becomes too wet, it may swell sufficiently to crack the rigid epoxy header.

   Caution: De-ionized water must be used. Nafion is a cationic exchange material, and when exposed to liquid water will exchange the hydrogen from the sulfonic acid with any cations in the water. 

4. Blow dry, oil-free compressed air through the dryer element tubing to remove any residual water.

   1. Begin blowing dry air through the dryer element quickly after wetting the element. This will minimize the risk of damage to the dryer due to swelling of the tubing.

   2. Continue for several minutes. This will reduce any swelling and restore the dryer to normal length.

5. If the element appears to be free of all salt deposits and remains relatively clear in color, proceed to Reassembly of the PD-Series Dryer.

Treatment of PD-Series Dryer Element with Methanol

When Nafion comes into contact with an alcohol (ie. Methanol), it will swell up to 188% of its original size, both in diameter and overall length. It is because of this characteristic that kinks in tubing can be repaired.

For collapsed tubing;

1. Remove the coupling from the shell.

2. Reinstall the element into the coupling only.

   1. Slide element into coupling through threaded end

   2. Push until snap ring seats

3. Reinstall the front nut.

4. Connect dry air to the sample inlet port, do not turn on flow.

5. Gently apply methanol to the element, do not go closer than 1.5 inches from the header.

6. Slowly begin to flow dry air through the tubing and allow to expand.

7. If there are still collapsed sections, apply methanol to those areas while air is flowing.

8. Once tubing is back to the proper shape, continue to flow dry air for several minutes.

9. Proceed to Reassembly of the PD-Series Dryer.

Acid Wash of the PD-Series Dryer Element

If oily residues are present, the dryer should be washed with acid to remove the residues and to recondition the Nafion (restore it to its original sulfonic acid form).

1. Prepare a bath of 10% nitric acid (HNO₃) in a suitable container. The container should withstand exposure to nitric acid and heating.

2. Immerse the Nafion tubing into the nitric acid bath taking care not to wet the epoxy headers. About 1.5 inches (4cm) of tubing as well as the header should remain out of the acid.

   NOTE:  Do not sharply bend the Nafion tubing during this cleaning process. The bath should be large enough to allow the Nafion to flex gradually. A magnetic stirring hotplate should be used if available. If not, the acid container should be heated in some fashion and stirred periodically.

   Caution:  Heating of the acid bath will generate noxious fumes. The cleaning process should be performed in a fume hood or very well ventilated area. Covering the container with a loose plastic lid will minimize the fumes.

   Caution: Rubber gloves and protective eyewear must be worn. Nitric acid at this concentration will stain and/or irritate the skin and injure the eyes if splashed. 

3. Heat the acid bath to 70°C to 80°C, and soak the Nafion dryer element for one hour with occasional stirring (a magnetic stirring bar set on low if possible).

4. Remove the dryer from the acid bath. The acid bath may be covered and reused until it shows significant discoloration.

5. Rinse the outside of the tubing and headers with de-ionized (DI) water at room temperature to remove the nitric acid residues.

6. Briefly force De-ionized water through the inside of the tubing. This may be accomplished with a plastic squeeze bottle or syringe. Do not immerse the headers of the dryer element in water or excessively wet the tubing inside the headers. Nafion tubing swells when exposed to water. If the tubing inside the epoxy headers becomes too wet, it may swell sufficiently to crack the rigid epoxy header.

7. Quickly blow clean, dry air through the dryer element to remove any residual water.

8. Continue to blow air through the dryer for several minutes. This will reduce any swelling and restore the dryer to normal length.

Reassembly of the Nafion Dryer

1. Install all (4) o-rings onto element.

2. Slide element into shell and coupling.

3. Install snap ring onto one end.

4. Push element into shell until o-ring seats.

5. Repeat for other end.

6. Tighten smaller set screw located in coupling threads, older models only.

7. Replace front nut.

8. Connect the sample inlet and outlet lines.

9. If necessary, reconnect the purge lines. Note that the purge inlet is at the opposite end from the sample inlet.