SEALS & BEARINGS FEATURE MOVING FROM COMPONENT TO CARTRIDGE AESSEAL M


any companies across the industrial spectrum use cartridge mechanical


seals almost exclusively on their pumps. Why? The fact is that although this type of seal was developed to limit emissions in hazardous, flammable and/or toxic services, they provide increased reliability and cost efficiency in virtually all applications and in all industries, from food and beverage to pulp and paper. Cartridge seals have a significant edge


over traditional component seals in the key areas of installation/assembly, repair/refurbishment and Inventory management. These benefits are felt not only in terms of bottom line gains for the company, but also in practical terms by staff responsible for maintenance, reliability and inventory management.


INSTALLATION/ASSEMBLY Traditional component seals are assembled into pump components during the pump build. This assembly process can cause premature failure and reduced reliability. The working length of the seal is either controlled by the mechanic assembling the seal drive screws on the shaft, or with a hook sleeve located on the pump shaft and held in place by the pump impeller. Such arrangements are susceptible to build tolerance stack-ups and are affected by any re-machining of pump components. An incorrectly set working length will negatively affect seal life and its ability to seal. Seal faces are made of hard, relatively brittle materials which are often damaged on installation. Gaskets or packings also risk damage. With a single component seal it is impossible to test the build until the pump is fully assembled. If the pump volute shares space with, or protrudes the pipe work (as in most pumps), testing can only be done when the pump is back in place in the pipe work. The test is often done when the valves are opened, resulting in inadequate process containment. Even with dual seals where an integrity test can be carried out using compressed air, test pressure is mostly limited to a few psi due to fear of the reverse pressure unseating a seal face. By contrast, cartridge seals are pre-


Typical dual cartridge seal cut away view


assembled and pressure-tested as a one- piece seal unit and the working length is controlled by the seal manufacturer. The cartridge is locked to the shaft at the end of the pump assembly and is unaffected by the tolerance stack-up of pump components or by the mechanic’s skill. Setting/transporting clips retain all seal components within the cartridge, protecting them during the build process.


REPAIR/REFURBISHMENT Unlike component seals, cartridge seals are easily boxed as a unit and sent back to the manufacturer’s trained team for repair or rebuild, with a typical turnaround of three days. A competent seal manufacturer records the condition of seal components as part of the repair programme. Trending or tracking repairs can provide detailed data on reliability improvement and measurement, and help identify the probable cause of failures. They also subject both new and repaired API cartridge seals to an integrity air test, providing assurance that sealing products have been correctly assembled. Using in-house maintenance staff for


seal repairs is a less-than-optimum use of valuable resources. Why make the significant training and equipment investment required to achieve a manufacturer’s standard of repairs when seal manufacturers have trained staff, often with several levels of competency, as well as the specialist equipment required?


API seal air test rig


Dual mechanical cartridge seal (DMSF)


INVENTORY MANAGEMENT With a large number of pumps across a factory or manufacturing plant, the seal component inventory can be substantial and its management complex. A typical component seal would consist of at least six parts for a single and at least ten parts for a dual seal. In a recent survey of a refinery storeroom, over 900 parts bins were required for a fleet of less than 230 pumps. According to inventory stewardship accountants’ rules of thumb, the management of inventory costs between five per cent and 20 per cent of the inventory value annually. With such a complex inventory, stewardship costs - including storage, part bins, procurement tax, inventory count, stocktaking, obsolescence, degradation (elastomers), breakages and losses - are likely to be closer to 20 per cent. If a cartridge seal strategy was adopted across the plant, the number of items held would be reduced by approximately 85 per cent. The overall stock value would also decline by approximately 30 per cent. With this significant simplification of the inventory portfolio the stewardship costs are also likely to be at the lower end of the scale, around five per cent, but further reductions could be achieved by a standardisation programme. If a site repair strategy was adopted, spares kits should be held as consumable parts, rather than individual components. Cartridge seals have been standardised


in the petroleum, natural gas and chemical industries since 1994 (API 682 1st Edition). But the benefits they bring from shop floor to boardroom is why they are increasingly becoming the first choice for companies with a strong focus on reliability.


AESSEAL www.aesseal.co.uk / FACTORYEQUIPMENT FACTORY EQUIPMENT | MAY 2018 23 T: 01709 369966


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56