Most Summa-type canisters and regulators are equipped with Swagelok™ compression fittings which connect to 1/4-inch outer diameter (OD) tubing, including Nylaflow, with Swagelok™ ferrules and a hexagonal nut. The nut can be reused, but the ferrules are not, except on stainless steel tubing. Many laboratories will provide Swagelok™ ferrules that fit their sample canisters at a nominal cost.
Because the Vapor Pin® sampling device was designed to be rugged and compatible with other sampling hardware, it has a nominal 1/4-inch barbed fitting at the top. Like other barbed fittings, it is actually somewhat larger than 1/4 inch in diameter, so the Vapor Pin® sampling device is joined to semi-rigid tubing, e.g. Nylaflow, with a short piece of soft tubing. Cox-Colvin offers Tygon™ R-3063 tubing to make these connections. Tygon™ offers better chemical resistance than other soft tubing, but is pliable enough to make a tight seal. The Tygon™ tubing is placed between the Vapor Pin® sampling device and the semi-rigid tubing and fits over both of them. Pressure gauges, tee fittings, and other devices with a 1/4-inch barb can be attached to the sample train with Tygon™ tubing. The sample train can also be assembled with compression fittings if desired, but the additional ferrules required at each connection adds to sampling time and costs. Also, in our experience, barbed fittings are less likely to leak than compression fittings, especially under negative pressure. In fact, Missouri’s 2004 vapor-intrusion guidance discourages compression fittings at all points except at the sample canister, due to their tendency to leak.
Tygon™ has better chemical resistance than softer tubing, such as silicone, but silicone’s high flexibility allows connecting devices of different diameters. Silicone can also be penetrated with a hypodermic syringe for some types of sampling, after which the tubing automatically seals the hole. As with all environmental sampling, make sure your equipment complies with regulatory requirements and Data Quality Objectives.
Please notice that chemical interference from tubing is dependent upon many factors, but tubing is more likely to contribute hydrocarbons than chlorinated compounds. To minimize the risk of chemical interference from all tubing, reduce tubing lengths as far as possible, particularly soft tubing, and keep tubing away from vapor sources during storage and transport.
