DIRTY and inoperable pressure- and vacuum-relief vents rank high on the list of cargo tank violations cited during roadside inspections, according to inspectors from the Department of Transportation. This is an issue that needs to be addressed by the tank truck industry. Speaking at the 1999 Cargo Tank Maintenance Seminar in Chicago, Illinois, Federal Highway Administration official Ted Turner said vents are not being cleaned at all or are being cleaned inadequately. This can compromise the safety of a cargo tank.
Plugged vents are something that shouldn't turn up on roadside inspections. Vents should be cleaned along with everything else when a tank trailer is washed out. Nothing is gained by cheaping out on these components.
Vents should be washed out with every tank cleaning. It takes maybe half an hour to remove, inspect, and clean a vent. That's not much added time or cost, especially when it is part of the regular tank cleaning process.
Vents can be cleaned of many products without disassembly. A high-pressure wand, detergent, and hot water may be all that is needed. In those instances when the vent must be taken apart, it should be bench tested to ensure proper performance after reassembly.
Vents aren't alone in needing more attention during tank cleaning. Other components also are ignored or missed. Discharge valves need to be disassembled and thoroughly washed. Seals need to be inspected and replaced if damaged or contaminated. Some wash racks replace the packing in Hydrolet valves after each cleaning.
Product pumps often are cleaned along with the cargo tank, but they need to be thoroughly inspected after cleaning and may need to be disassembled if a particularly viscous or aggressive product was handled. Product can collect in nooks and crannies throughout the pump.
Product hoses may be cleaned with the tank or soaked in a vat. That may not be enough, though. Product can collect in gaps between the hose and the hose fittings.
Product residue in any component can result in load contaminations, which can pose serious health hazards in foodgrade operations. Chemical loads also can be damaged by contaminations, which can bring costly claims for tank truck carriers.
Contamination may be the smallest of problems if pressure- and vacuum-relief vents are plugged. Tank integrity and operating safety can be jeopardized by vents that are contaminated to the point that they no longer function properly or at all.
A contaminated vent may open only partially, resulting in reduced venting capacity. This will become more of a concern for vacuum vents as closed-loop chemical loading and unloading and vapor recovery become more widespread in the future. The industry could see more collapsed chemical tanks if vacuum breakers aren't kept in good operating condition.
Tank components need just as much cleaning attention as the cargo tank itself. The job isn't done until every item that comes in contact with the cargo is scrubbed clean.