Maintenance
2.6.1 Sampler
Maintenance of the sampler is required from time to time. Special attention should be paid to:
• Rotameter flow rate: It is recommended to check the rotameter flow rate once per month. The rotameter flow rate should be about 10% higher than the flow rate observed on the volume meter.
• Open flow test and leak test: It is recommended to check for optimal flow conditions from time to time. Depending on the sampling location and the setup of the sampling station, this test should be performed once a week or at least once a month.
The following procedure is recommended:
A. Fully close the valve – the rotameter flow rate should be zero (0), the vacuum should read about -0.8 bar and the volume meter gauge should not move. If these three conditions are fulfilled, the tubing from the valve to the pump is ok. If the conditions are not fulfilled, the tubing from the valve to the pump is not vacuum tight. Start searching for the vacuum leak and repeat test A as long as conditions are fulfilled.
B. Fully open the valve and no SFU connected - By closing off the transparent tubing temporarily, e.g. with a small rod or even a finger, the rotameter flow rate should again be zero (0) flow rate, the vacuum should again read -0.8 bar and the volume meter gauge should not move. If these conditions are fulfilled, the tubing from the SFU to the pump is ok. If the conditions are not fulfilled, the tubing from the SFU to the valve is not vacuum tight. Start searching for the vacuum leak and repeat test B as long as conditions are fulfilled. Cause of the vacuum leak can for example be that somebody stepped on the fragile POLY-FLO tube (mechanically deformated) or put a heavy weight on the tube. Replace the leaking part of the tube before commencing air sampling. Repeat test B until conditions are fulfilled. Page: 18
The tubing will also become brittle from exposure to sunlight and should be replaced periodically.
C. Connect the SFU without loaded filters and check that the flow rate is setup to 16 – 17 l/min by manually adjusting the valve. Test C is probably the most important test because this test reveals if there is a problem with the tubing from the SFU to the valve and to the pump. However, all three tests must be performed regularly to ensure a proper operation of the air sampling unit.
2.6.2 Black polyethylene container
Cleaning of the container is required on a regular basis, e.g. every 2-4 weeks. Take the container apart and clean it with water and ethanol. Figure 9 shows overview and detail images of the assembled black polyethylene container.
Greasing of the pre-impaction plate
After cleaning with ethanol, apply a thin layer of grease to the pre-impaction plate using Apiezon vacuum grease type AP101 (or type H) to minimize the particle bounce-off.
Note: do not use silicon-based or silicon-containing grease for contamination reasons. Make sure that the grease is silicon-free by carefully reading the documentation that came with the grease. Note that many vacuum grease applied to O-rings in vacuum systems do contain silicon. Double check that the grease applied to the pre-impaction plate is silicon-free.
It may be necessary from time to time to pull the pre-impaction plate out of the unit for cleaning purposes. For this cleaning purpose, pull one or two rods that hold in the pre-impaction plate in place carefully out. Do not apply excessive force – they are breakable! The rods are retractable and can be pulled out carefully from the grove located in the inner surface of the container. Clean the pre-impaction plate with ethanol and make sure that a thin layer of grease is applied before re-assembling.
2.6.3 Stacked filter cassette
Cleaning of the stacked filter cassettes – after having used the unit for, say 6 sampling periods, i.e. every 3 weeks based on sampling twice a week, the filter cassettes should be cleaned.
1. For this maintenance disassemble the stacked filter cassettes completely.
2. Prepare detergent solution.
3. Prepare two solutions of distilled or deionised water (named here solution A and B, respectively).
4. Prepare dilute solution of nitric acid (0.001 molar).
5. Clean all parts including the O-rings, the lids and the screw cap in the detergent solution.
6. Clean all parts that are in contact with the Nucleopore filters, i.e. support grids and filter retaining rings, in the dilute nitric acid and subsequently in distilled or deionised water (use solution A).
7. Clean remaining parts only in distilled or deionised water (use solution B).
8. Assemble the cleaned stacked filter unit. Make sure that the filter support grids are inserted correctly. The grids are marked four (4) times with UP at the edge. The flat edge of the grid is now facing down to ensure that the O-ring seals tightly. The support rings fit in one direction only. Make sure that the support rings fit nicely. Tighten the stacked filter unit, but don’t over tighten it.