Air sampling can be more involved and more difficult at times than sampling for water and solids. For example, a leak cannot be easily identified when collecting an air sample like it can be with water. The following instructions provide an overview of sample collection for general purpose to help ensure something like a leak does not affect the sampling and impact the data. To learn more about air sampling equipment, please check out the Air Sampling Equipment Guide blog.
Shut-In Test for 3 and 6 Liter Canisters
Attach the flow regulator or other equipment to the canister. Tighten the fitting with your fingers first, then tighten gently using a 9/16” wrench. Be sure equipment is closed off from the environment. Open the canister valve counterclockwise approximately 1 ¼ turns, and leave it open for roughly 10-15 seconds. After the time has elapsed, turn the valve clockwise to close. The canister valve is left open for 10-15 seconds in order to allow the closed system to equilibrate. After the valve is closed, observe the vacuum gauge for approximately three to five minutes. If the vacuum gauge shows a change in pressure re-tighten all fittings and continue to observe if the canister retains its vacuum. If the canister retains pressure, it is considered to be “leak-tight.” Ensure the valve is closed and continue with Canister Sampling Instructions for a Grab Sample or Composite sampling.
Grab Sample
If collecting a Grab sample, disconnect the brass cap from the top of the 3- or 6-liter canister and connect the canister to the sampling port via tubing or a sample train. Open the canister valve, turning the valve counterclockwise. Then turn back clockwise slightly until resistance is detected. If collecting the sample with a 1.4-liter canister, the sample point will need to be connected via the quick connect fitting which opens the valve on the canister. A grab sampler can be rented out and connected to the 1.4-liter canister to allow the grab sample to be collected.
Composite Sample
If collecting a Composite sample, disconnect the brass cap of the 3- or 6-liter canister and attach the flow regulator to the canister. Tighten the fitting with your fingers first, then tighten gently using a 9/16″ wrench. A shut-in test should be performed to ensure there are no leaks between the canister and the flow controller. To begin sampling, turn the valve counterclockwise until there is no resistance. Then turn back clockwise slightly until resistance is detected. If a 1.4-liter canister is being used, the flow controller will be fitted with a quick connect fitting, allowing it to attach directly to the canister and sampling to begin.
Sampling Completion
At the end of the sampling period, close the canister valve of the 3- or 6-liter canister by turning the knob clockwise. Do not tighten with a wrench. If using a 1.4-liter canister with a quick connect fitting the grab sampler or flow controller can just be removed from the canister. This closes the valve and stops sample collection. Remove all attached equipment from the canister and replace the brass cap on the canister valve on a 3- or 6-liter canister. Tighten the brass cap a quarter turn past tight using a 9/16″ wrench.
Enthalpy can perform many analyses on differing matrices of air. We provide silanized summa canisters which makes them inert from reacting with the gas samples. This is important as un-silanized canisters can react with an air sample which can make the data less meaningful and damage the canister used.
For more information on air sampling equipment and the analysis please contact us here.
