Gear pumps are very commonly used for the pumping of AN-water based emulsion products for both handling and blast loading applications. The potential major hazardous problems likely to be encountered with these pumps are: (ⅰ) high probability of friction; (ⅱ) possibility of product confinement in the area of the bushings; (ⅲ); high bearing failure rate; (ⅳ) pump running dry; (ⅴ) presence of foreign material; (ⅵ) deadheading of pump; (ⅶ) delamination of elastomer from steel gears. Of all these possible scenarios, the no-flow situations where the pump is running dry or deadheaded have always been recognized as the most serious ones. In the present study, a 3 in (76 mm) gear pump was tested under both dry-running and deadheading conditions with several repeats to establish how variable the results would be. Approximately 40 different tests have been conducted. The tests were performed with a gear rotation speed 20% higher than the maximum normally allowed in the explosives industry. The tests were also performed using an electric motor capable of delivering 3 to 4 times more power than that normally used in actual explosives applications. The pump was heavily instrumented with several thermocouples and pressure transducers. An infrared camera was also used to get information about the evolution of the surface temperature field of the pump. It was found that, under dry-running conditions, very high temperature spikes (close to 300°C, 570℉) could be observed at specific locations inside the pump. These are thought to be due to local burning of either the emulsion or the gear elastomer. However, due to the very small quantity of product present in the pump during this type of event, none of these events was found to degenerate into an explosive event. Under deadheading conditions, it was found that with new gears installed according to the manufacturer’s recommendations (clearance to side plates), the pump could not be started. Invariably, the pump drive shaft would break and the gears would therefore not turn. If gear elastomer wear was simulated, allowing slippage of product, by increasing clearance between the gears and the side plates, it was found that the pump could then be started in deadhead configuration. However, it was found that temperatures were limited to 140°C-220°C (284℉-428℉) due to breakdown of the product and/or delamination of the gear elastomer. In ten repeats of each test, for both open and blocked suction configuration, no explosive event was observed.
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