ABSTRACT
Pumps are devices with glands that leak. Packed glands are cheap and simple and rarely fail catastrophically, but there is usually a slight leak, and they need regular adjustment. Mechanical seals are therefore widely used, often with a second seal to contain any leakage. They require skilled assembly and accurate shaft alignment. Canned motors and magnetic drives eliminate the need for seals, but their initial cost is high. When experience shows that pumps handling problematic liquids are particularly liable to leak, for example, those handling very hot or cold liquids, remotely operated emergency isolation valves should be fitted in the suction lines so that leaks can be stopped from a safe distance.2 All glands may fail catastrophically if there is a bearing failure. If the quantity of liquid in the suction vessel is large, then emergency isolation valves should be installed even though the pumps have no history of failure. Otherwise, if failure should occur, a large quantity of liquid will be discharged.
