ARCHIVED REPORTS_1988_2 - Laserfiche WebLink

Home Browse Search

Recent inquiries from other experts in the field requesting that we supply them with these specially possivated canisters indicates that their inherent superiority over bags is becoming more widely recognized. For example, canisters can be pressurized for more convenient leak testing. The CCAS canisters are sealed both by the needle valve and by Swagelok, cap to doubly prevent losses while bags have only a single seal. Bag samples must be overwrapped to protect the samples from light while cons are opaque. Bags are fragile while cons are not. Bags cannot withstand air shipment in a depressurized environment while cans are readily shipped by air. Although bags are cheaper than cans, they are difficult to clean while canisters can be rigorously cleaned using moist zero air, heating, flushing and evacuation. Since bags really should not be reused at all, overall costs are actually cheaper if canisters are used in place of bags. INTEGRATED SAMPLING PROCEDURE This sampling procedure is applied when regulatory requirements on program needs mandate continuous sampling over on extended period of time such as is the case with Calderon monitoring. The sampling system is controlled by a programmable timer which, in turn, activates a stainless steel/Teflon pump and a solenoid valve. The system incorporates a relief valve and a flow controller in order to ensure a constant flow of air into the sampling manifold. The arrangement of components within the all -stainless steel/Teflon system is provided in figure 2. CCAS is presently developing a second integrated sampling system modeled after a very similar EPA apparatus in which a restrictor is placed ahead of the pump in the sampling train. Both systems deal effectively with the problem of drawing samples into a canister which begins under vacuum and finishes under pressure. Prior to initialization of sampling, an electropolished steel canister (preferred) or cartridge or Teflon/Tedlar bag is connected to the manifold. The manifold is then flushed with ambient air through the three®way boll valve/vent shown in figure 2. The connections to the sampling container is then opened and the system is ready to be activated by the timer. For example, if a 24 hour sampling period is desired, the timer would turn on the pump just prior to the desired time (ie 10:00 AM). A few seconds later the solenoid valve would open to admit the sample to the containers or cartridges. If canisters are employed, progress may be monitored by means of the pressure/vacuum gauge positioned on the manifold. Flow may be regulated via the controller to ensure that the capacity of the sampling system is not exceeded during the desired sampling period. In this way sampling periods as long as 24 hours can easily be accommodated. Futhermore, the solenoid valve may be connected to a wind direction sensor so as to trigger on automatic valve closure in the event of an inappropriate wind shift. The systems may be set up to start and stop without the presence of an operator so that extra labor is not required in order to tend multiple samplers.