The Reston Groundwater Dating Laboratory
Troubleshooting CFC sampling
Problem: Gas in water
- Is it real? Is the water outgassing?
- Loose connection somewhere; at well, pump, back of instrument
- Is N2 gas pressure too high (should be around 25 psi)?
- Are you or have you been pumping sand? Pump may be damaged (in case of Bennett pump); or sand may has scratched valve on apparatus.
Problem: No gas flow, can't clear the ampoule stem for sealing.
- 1/8 inch Cu tubing at molecular seive has cracked, losing gas.
- 1/16 inch stainless steel tube has cracked
- Forgot to open both valves on N2 regulator
- Pressure at 1st stage regulator on N2 needs to be about 25 psi
- Tighten nut around ampoule and stem on 1/8 inch tube that goes inside the ampoule.
- Replace ferrules in nut and stem.
- Pinch tygon tubing tighter.
- Are the ferrules assembled in the proper order?
Problem: Glass inflates on melting and bubbles out
- Tygon tube behind apparatus is in water or somehow blocked.
- Flame too high
- Too much water in stem. Empty stem so meniscus is at bulge in stem.
- Keep flame higher on stem, above water in neck.
- Check gas flow rate; regulator at 25 psi
Problem: No or limited flow of water
- May have particle blocking flow in inlet tube
Problem: Ampoule breaks while connecting
- Bad ampoule, thin glass
- Broken glass fragments in ferrule
- Was ferrules of broken glass
- Ampoule size may not be just right. If too small, wrap with Teflon tape. If too large, get another ampoule.
Problem: 1/8 inch stainless steel stem does not slide freely.
- Stem is bent. Try removing and straightening by rolling against a flat surface
- Use replacement stem taped inside lid of shipping box.
- Avoid over-pack shipping box
- Careful not to over-heat stem and melt ferrule
- Avoid "bird art" in stems. Make short, blunt seals
- Careful with flame in general
- DO NOT HEAT VALVE IN APPARATUS
- Be careful with the equipment. It arrived in good shape and should be returned as such.
- Don't hold on to the equipment, if not using it for 3-4 weeks. We will check it out, make sure it is "clean" of CFCs and ship it back when you need it.
- Packing ampoules for shipping - no samples in outer edge of box. Bubble wrap on top. Seal box. Double-box samples.
- Ship ampoules and equipment next day Federal Express.