Silicon carbide bushings are critical to the design of a new two-stage pump whose seal-less design helps prevent production losses. Positive displacement pumps are normally used in applications such as cooling systems that have a relatively small flow system yet require a high flow rate. These pumps provide good performance in these applications but are quite expensive and are vulnerable to seal failures that cause a considerable amount of downtime. Price Pump has targeted these applications with a new design that achieves high pressure at low flow rates by using a two-stage rather than a positive displacement design. This approach offers significant cost advantages because it inherently requires fewer sealing features, but Pawel Bankowski, Director of Engineering for Price Pump, was determined to go one step further by improving reliability with a seal-less design. He used a magnetic drive to eliminate the mechanical seals by sealing the impeller and its housing completely.
Yet, while magnetic drive pumps eliminated the need for mechanical seals, they did not eliminate the problems associated with them completely. Magnetic drive pumps still require bushings and washers to maintain the position of the impeller shaft and this bushing, while rotating, generates heat. As the company was developing the new pump, obtaining good performance from these bushings was a major challenge. Designers started with several different types of carbon graphite and ceramic bearings. The problem was the magnets used to drive the pump generated very strong forces that could easily break the bushings and washers while they were being assembled. Usually, the assembler didn’t even notice that the bearings had broken. Then, when the pump was turned on for testing, additional damage would usually occur to expensive components. Another problem was that these bearings did not provide the required level of run dry capability.
Engineers from Morgan AM&T, suggested Grade PGS-100, a patented sintered silicon carbide that contains an optimum amount of free graphite evenly dispersed throughout the material matrix. The free graphite enhances lubrication at the operating interface during the upset condition, prolonging the time between process upset and catastrophic failure. Morgan engineers worked with Bankowski to design wear components to meet the requirements of the application. “The new bushings and washers worked perfectly,” Bankowski said. “We haven’t seen a single example of breakage since we began using them. At the same time, our testing quickly determined that they were easily capable of surviving in run dry mode long enough for the automatic shutoff to kick in. The new step was wear testing and we found that no matter how long we tested these bushings we were never able to get them to wear out in normal usage. Even after extended test runs, there were no signs of wear. They are providing outstanding reliability and performance to our customers.”
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Yet, while magnetic drive pumps eliminated the need for mechanical seals, they did not eliminate the problems associated with them completely. Magnetic drive pumps still require bushings and washers to maintain the position of the impeller shaft and this bushing, while rotating, generates heat. As the company was developing the new pump, obtaining good performance from these bushings was a major challenge. Designers started with several different types of carbon graphite and ceramic bearings. The problem was the magnets used to drive the pump generated very strong forces that could easily break the bushings and washers while they were being assembled. Usually, the assembler didn’t even notice that the bearings had broken. Then, when the pump was turned on for testing, additional damage would usually occur to expensive components. Another problem was that these bearings did not provide the required level of run dry capability.
Engineers from Morgan AM&T, suggested Grade PGS-100, a patented sintered silicon carbide that contains an optimum amount of free graphite evenly dispersed throughout the material matrix. The free graphite enhances lubrication at the operating interface during the upset condition, prolonging the time between process upset and catastrophic failure. Morgan engineers worked with Bankowski to design wear components to meet the requirements of the application. “The new bushings and washers worked perfectly,” Bankowski said. “We haven’t seen a single example of breakage since we began using them. At the same time, our testing quickly determined that they were easily capable of surviving in run dry mode long enough for the automatic shutoff to kick in. The new step was wear testing and we found that no matter how long we tested these bushings we were never able to get them to wear out in normal usage. Even after extended test runs, there were no signs of wear. They are providing outstanding reliability and performance to our customers.”