PSS provides emergency discharge control
Aug 1, 2003 12:00 PM
The new Passive Shutdown System (PSS) from MSA (Mine Safety Appliances Co), provides emergency discharge control for MC330 and MC331 cargo tanks as required by DOT HM-225A (49 CFR 173.315).
This system automatically shuts off the flow of product without human intervention within 20 seconds of an unintentional release caused by the complete separation of a liquid delivery hose. This system can be used to monitor leaks of propane, anhydrous ammonia, and dimethyl ether.
The PSS is mounted on the vehicle framework under the cargo tank and is activated before the driver begins product delivery. A catalytic combustible sensor continuously monitors transfer of product, detecting any gas released during discharge due to a hose separation, hose leak, or valve leak. The amount of gas present is converted into a percentage-LEL (lower explosive limit) reading. When the detection limit of 10% LEL is exceeded, the unit goes into alarm mode. This triggers immediate shutdown of the primary valve, closing discharge, fill, and vapor lines.
Housed in a stainless steel, explosionproof enclosure, the PSS meets NEC Class I, Division 1 hazardous location installation requirements, and is provided for both cable and air systems. It is UL-approved and has Design Certified Engineer (DCE) certification. For complete details, contact MSA, PO Box 427, Pittsburgh PA 15230.
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