Section 10 - Special Problems with Cabinets

1. Blowers running backwards
   

   Blowers in Class II cabinets usually cannot be made to run backwards but the external blowers on Class I cabinets and Class II type B cabinets usually have reversible motors. When running backwards, they still deliver air flow, but at reduced volume flow. Whenever insufficiency in air flow is noted in a new cabinet, direction of blower rotation should be checked.

   In a system with 2 blowers, both blowers must be started at the same time. If one starts substantially ahead of the other, the second blower may run backwards. Verify that if independent, the speed controls are set at equal voltage setting.

2. Controls located in contaminated section of the cabinet
   

   Older cabinets prior to the NSF International Standard have controls, switches, ballasts, etc., in the contaminated part of the cabinet. These cabinets must be decontaminated, appropriate precautions taken and/or proper Personal Protective Equipment taken before servicing these parts if they have been used for work involving hazardous materials.

3. Flowmeters units
   

   Cabinets that have a rotameter-type flowmeter on the control panel to give an indication of air flow. There are two tubes located in the supply blower, one with holes facing into the air flow and the other with holes facing the other way. Air flows through connecting tubing to the flowmeter and back through connecting tubing to the other tube. The air flow is adjusted with an integral valve until the rotameter float rises to the indicated height. Because the connecting tubes are located on the dirty side of the HEPA filters, they become dirty during use and should be cleaned and blown out at every filter change. If not properly cleaned, dirt will eventually plug the tube to the flowmeter and cause low or unreliable readings. The cabinet must be decontaminated, appropriate precautions taken and/or proper Personal Protective Equipment taken before attempting to clean or service this unit.

4. Moveable sash wiper seals
   

   Cabinets with sliding sashes have wiper seals behind the view screen. When these wiper seals deteriorate, laboratory air can be sucked into the work zone. This deficiency can be detected with a smoke source generated outside the cabinet and checking for penetration inside. Replacement wiper seals should be installed to correct this deficiency.

5. Speed controls
   

   Newer model cabinets by various manufacturers now incorporate speed controller that compensate for voltage fluctuations. Initial field problems by a few manufacturers resulted in wiring upgrades and/or replacement of newly designed speed controllers.

6. Electrical support devices
   

   See electrical troubleshooting section but due to age and use; relays, pilot lights for operation, alarm indications, micro switches and others tend to wear or burn out and may be more nonsense problems than performance problems. At the time of testing, the above should be checked for proper operation.

7. Internal diffusers, soundproofing or prefilter
   

   Some style Type B1 cabinets particularly older units incorporated closed foam type supply diffusers. These were typically located above the work surface and over time tend to breakdown and shed large black particulate. At time of testing one may run their gloved fingers along the foam diffuser to check the current condition. If brittle replace with OEM (Original Equipment Manufacturer) foam. This would also apply to older cabinets with soundproofing. If used with hazardous material, a decontamination or appropriate PPE shall be donned. Lastly are prefilters if brittle or dirty replace as necessary.

8. 3rd HEPA filters above work surface
   

   On newer style Class II Type B1 incorporate a third HEPA filter above the work surface. Typically, this HEPA filters only purpose is to clean the air which passes across the motor/blower assembly. Since the primary HEPA filter is located under the work surface tray and leak tested, the filter typically does not require the standard leak test. It acts like a diffuser and provides HEPA filtered laminar flow air at the work zone.

9. Internal dampers, screens, diffusers
   

   As for the motor and impeller whenever a cabinet is opened for service, decontamination or appropriate PPE when contaminated, all internal dampers, balancing screens, diffusers and airflow monitors should be thoroughly cleaned prior to re-assembly. This will potentially eliminate any motor overheating and restriction airflow problems. On a few models, screens, etc. are hidden from view (i.e. rear wall under work deck).

10. Operational hardware
    

    During and at completion of the testing of the cabinet, various operational hardware should be inspected and replaced if necessary. That would include:

    1. Hinges - look for wear
    2. Switches - proper operations
    3. Latches/closure devices - look for wear and proper compression
11. HEPA filter seals
    

    At one point, for a limited time, some manufacturers incorporated a "liquid seal" type HEPA filters. Initially, this seal was a compound similar to high vacuum grease. But tended to dry out and bypass leakage resulted. To correct this problem field retrofit kits were available (custom ordered) to replace the liquid seal knife edge with a standard clamping surface so closed cellular type gasketed HEPA filters can be utilized.

12. Motor maintenance
    

    Some manufacturers incorporated motors that require lubrication once a year or each HEPA filter replacement. 20-30 drops of SAE-20 non-detergent or electric motor oil should be used.

13. Other problems
    

    When problems are encountered that are not covered in this manual, the cabinet manufacturer should be contacted. Listed below are manufacturers phone numbers:

    
    
    
    
    
    
    
    
    
    
    
    

    Baker Company, Inc. Sanford Airport Sanford, ME 04073 (207) 324-8773	Germfree Laboratories, Inc. 7435 N.W. 41st Street Miami, FL 33166 (800) 888-5357
    Becton Dickinson Microbiology Systems 250 Schilling Circle P.O. Box 243 Cockeysville, MD 21030 (505) 345-3561	Hitachi Ltd. 4-6 Kanda Surugadai Chiyoda-Ku Tokyo 101 Japan 032581111
    Bellco Glass, Inc. 340 Edrudo Road Vineland, NJ 08360 (609) 691-1075	Labconco Corporation 8811 Prospect Kansas City, MO 64132 (816) 333-8811
    CCI (no longer in existence) contact Forma Scientific Envirco Corporation 6701 Jefferson N.E. Albuquerque, NM 87109 (505) 345-3561	Microzone Corporation (formerly Canadian Cabinets, Ltd.) 25F Northside Road, Box 11336, Station H Nepean, Ontario, K2H7V1 Canada (613) 829-1433
    Forma Scientific, Inc. P.O. Box 649 Mill Creek Road Marietta, OH 45750 (800) 848-3080	Nuaire, Inc. 2100 Fernbrook Lane Plymouth, MN 55447 (763) 553-1270