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FEATURE PUMPS, VALVES & ACTUATORS COST V. PERFORMANCE – AVOIDING A FALSE ECONOMY


Despite being considered outdated, the comparatively low cost of gland packing means many companies continue to use it. But, asks David Amory of AESSEAL, is it a false economy?


M


echanical seals are small components when considered in the


overall context of an industrial plant and it can therefore be easy to underestimate their relevance. But their function - to prevent fluid


leaking from the shaft region of pumps and other rotating equipment - is fundamental to operational efficiency. They have a significant impact on maintenance budgets and downtime. There has been a step-change in the


design and efficiency of mechanical seals since they first arrived on the market more than 80 years ago. In contrast, traditional gland packing is a sealing principle which dates back to ancient Greece and comprises a compressed, lubricated material which is literally packed around the pump shaft to physically stuff the gap. More durable synthetic packing materials have been developed, but the inherent drawbacks of gland packing remain. To achieve the most effective seal, gland packing must press tightly against the


rotating shaft. This friction gradually wears away the packing, causing leakage. In an ideal scenario, correctly adjusted gland packing should be maintained with a leakage rate of one drop per minute of sealed product per 25mm of outside shaft diameter, equating to 450 litres a month or 5,400 litres a year on a 50mm diameter shaft. In reality, leakage rates can be ten times higher, so consider the cost for lost product valued at 50p per litre. Gland packing can eventually wear a


groove into the pump shaft, requiring costly repair or replacement. The risk of overheating must also be mitigated, meaning it must be flushed with large volumes of cooling water. The pump may require more drive power and, therefore, energy consumption, to turn the shaft – creating an environmental and financial concern. Constant maintenance is essential to offset the negative impact of gland packing. So why choose it over mechanical sealing solutions? Common reasons are its cheaper initial cost and short-term convenience -


By looking beyond the price tag and rethinking ingrained maintenance practices, replacing gland packing with mechanical sealing solutions can lead to gains in operational and financial efficiency


carrying out regular maintenance and repacking while the pump remains in service simply becomes an accepted part of operational routine. Yet consider the long-term benefits of ‘more expensive’ mechanical seals, and the perceived benefits of using gland packing quickly diminish. In fact, there are few exceptions where it is a more effective solution. Mechanical seals have no visible leakage. And with just 0.002% of water contamination to lubrication oil estimated to reduce bearing life by almost half, that alone should make the case for an upgrade. With properly specified and installed mechanical seals, effluent disposal costs are also eliminated. Product is protected from dilution and airborne pollution is reduced. Mechanical seals require no ongoing


maintenance. They cause no wear to the pump shaft or shaft sleeves, saving on costly repair or replacement. To understand the scale of return on


investment (ROI) by upgrading to mechanical sealing solutions, take the example of a global food and beverage manufacturer, which was experiencing a MTBF (Mean Time Between Failures) of just two months on a vertical mixer processing starch at its starch and sweetener processing plant in Poland. The gland packing on the mixer was


David Amory from Aesseal VALVE WITH ONE MOVING PART ELIMINATES POTENTIAL LEAKS AND EMISSIONS


Oxford Flow has launched its IM gas regulator valve to increase reliability and reduce costs for operators in the gas distribution, power generation, industrial gases and oil and gas sectors. The launch follows a successful ongoing trial with SGN where the valve has been installed and


commissioned with ease, regulating gas pressure smoothly with rapid changing demand profiles within an Accuracy Class of 1.5%. This valve accuracy enables utilities and operators to achieve faster network stability on commissioning, even where flow rates vary significantly. In addition, the valve’s compact construction reduces weight and the need for lifting equipment during installation and maintenance. In conventional valves, the diaphragm tends to be the most common failure point. Oxford Flow’s design


has eliminated the diaphragm, stem and external mechanical actuator. With only one moving part, the design minimises potential leaks and the risk of fugitive emissions – maximising efficiency and reducing maintenance costs. Neil Poxon, CEO at Oxford Flow, said: “As many companies across the industries


we serve look for ways to minimise costs, this gas regulator enables just that. Our recent valve testing and developments in the UK, Germany and USA have enabled us to improve and perfect the regulator so that we can now roll the technology out to the wider industry with confidence.” Oxford Flow


oxford-flow.com 16 SEPTEMBER 2019 | PROCESS & CONTROL


leaking and causing seal and, subsequently, bearings failure. Packing replacement and maintenance cost the company almost £5,000 a year, in addition to the cost of lost production. The vertical mixer operated under high pressure, generating vibration. This, combined with the pressure of the packing, also led to premature wearing of the shaft axial. AESSEAL replaced the gland packing with a cartridge double mechanical seal specifically designed for mixers, where radial shaft movement caused by vibration is common. The seal was designed to accept radial movement up to 1.5mm. Inboard seal faces were made from tungsten carbide and outboard faces from tungsten carbide and carbon. Labyrinth style bearing protector seals, which exclude moisture and other contaminants, were also installed. The new seal and support system


eliminated the problems of leakage and wear and achieved an increase in MTBF of 1,700%. The company saved £3,450 within the first year on packing replacement and maintenance costs and achieved a ROI within four months. Total savings to date are £10,300.


Aesseal www.aesseal.co.uk


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