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AN12-1: Pressure Port Oil Refill Procedure and Nylon Capillary Fitting Replacement

Document Number: 
Publication Date: 
Friday, September 12, 2008
PDF icon appnote12-1Sep08.pdf416.02 KB


This Application Note describes the refilling of the pressure capillary tube and replacement of the nylon pressure capillary fitting for the following instruments:

Note: The nylon pressure capillary fitting — which includes a pressure port fitting and an external capillary tube — is filled with silicone oil. The oil transmits hydrostatic pressure via internal, stainless steel, capillary tubing to the pressure sensor inside the instrument, and prevents corrosion that might occur if the sensor diaphragm was exposed to water. The internal tubing and nylon capillary fitting are vacuum back-filled at the factory. Because of the viscosity of the silicone oil and capillary action, the silicone oil does not run out of the external capillary tube. However, due to temperature and pressure cycling over long periods, it is normal for some oil to slowly leak out of the external capillary tube. When the oil is not visible or is receding inside the translucent tube, or if the fitting has been damaged, refill the oil.


Prepare P/N 50025 Pressure Sensor Oil Refill Kit

P/N Description Quantity
30419 Syringe for injecting DC-30 1
30420 Needle (21 gauge) for syringe 1
30421 76 m (3 inch) long FEP tubing (1/32 inch I.D.; 1/16 inch O.D.), to place on end of syringe needle 1
30410 Dow Corning DC-200 oil (20 centistokes viscosity) 1 ounce
30422 Bottle for 30410 oil 1

To replace the needle (if necessary):

  1. Use a 21-gauge surgical needle, minimum 25 mm (1 inch) long.
  2. Grind off the tip so the needle is no longer sharp.
  3. Remove any burrs.
  4. Verify that the needle still has a hole through it.
  5. Screw-lock the needle into place on the syringe.


Remove Nylon Capillary Fitting and Refill Pressure Sensor Capillary with Oil

  1. Seal the end of the glass conductivity cell (using Tygon tubing or similar material) to avoid contaminating the cell with oil.
  2. Unscrew the nylon pressure capillary fitting (P/N 50029) from the end cap pressure port. The fitting contains silicon oil, so there will be some spillage.
    CAUTION: Be careful not to hit the glass conductivity cell with the wrench, as doing so will break the cell.
  1. Calibrate the pressure sensor (if desired):
  1. The end cap pressure port is tapped with a 5/16-24 straight thread to accept your pressure fitting. Use a fitting that has an O-ring face seal, such as Swagelok-200-1-OR.
  2. Calibrate the pressure sensor.
  3. Remove the pressure fitting.
  1. Turn the instrument so that the end cap faces up.
  1. Fill the pressure sensor internal capillary with oil:
  1. Fill the syringe with DC-200 oil.
  2. Insert the syringe’s FEP tubing as far as it will go into the pressure port’s internal capillary.
  3. Fill the internal capillary with oil, slowly pulling the syringe tubing out of the capillary as the capillary fills. Make sure to keep the tip of the syringe tubing below the oil surface as you pull out the syringe. When filled, a slight meniscus forms at the surface of the end cap.
  1. With the end cap still facing up, reinstall the nylon pressure capillary fitting on the end cap. Do not overtighten the fitting. The oil from the internal capillary should fill the fitting and overflow the top of the external capillary tube as the fitting is screwed in. If it does not, repeat Steps 2 through 6 to fill with additional oil.
  1. Clean up any spilled oil on the instrument.
  2. Remove the material used to seal the end of the glass conductivity cell.


Application Note Revision History


Date Description
  Initial release.
September 2001 Revise, add pictures.
September 2008 Add applicability to 16plus, 16plus-IM, 16plus-IM V2, and 19plus V2 when equipped with Digiquartz pressure sensor.


Applies To