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Look beyond the price tag for cost-efficient seals

Look beyond the price tag for cost-efficient seals

Cost should not be the only consideration when selecting mechanical seals for pumps and other rotating equipment, says Paul Green of AESSeal. To achieve a better return on investment, a wise buyer also looks for factors such as reliability, traceability and customer service.

It’s a common scenario across countless industries: downtime due to recurring problems such as pump leakage or the bearings failure brought about by it. The maintenance manager curses the inconvenience and cost of interruption – then promptly implements a sealing solution identical to the one that was at the root of the disruption.

When mean time between failure (MTBF) can be as short as a couple of weeks it’s easy to see how the habit develops to keep using the same sealing methods when the product is already on the maintenance shelf, is relatively cheap and has been installed so many times you could virtually do it with your eyes closed. This approach may seem the cheap and easy option but it can be more costly – financially and environmentally – down the line.

The worst culprit for causing operational downtime is traditional gland packing. Although the initial cost of gland packing is low compared to a mechanical seal, it has inbuilt drawbacks:

  • Friction caused by the rotating shaft causes the packing to wear over time, leading to repeated leakage of the process fluid such as water or paper pulp for example.
  • Heat caused by the friction means the packing has to be flushed with large volumes of water to keep it cool.
  • More energy is needed to turn the shaft due to the pressure of the gland packing.
  • This pressure eventually wears a groove into the shaft or shaft sleeve, which can be expensive to repair or replace.

For companies with a commitment to the environment as well as the bottom line, the argument for upgrading to mechanical seals and support systems is strong. The optimum gland packing arrangement has a leakage rate of one-drop per minute of sealed product per 25mm of outside diameter shaft, a 50mm diameter shaft would see total leakage of 450 litres a month, or 5,400 litres a year. We know from experience that realistic leakage levels tend to be 5-10 times greater.

By contrast, a well designed, specified and fitted mechanical seal will lose the equivalent of half a teaspoon of product a day. For a product costing 50p a litre this would see a return on investment on even an advanced mechanical seal of around six months. And this is before taking into account:

  • Operational savings gained from new MTBFs that generally run into months and years.
  • The environmental and cost benefits of having no effluent to dispose of.
  • Power consumption roughly six times less than gland packing.
  • Improved bearing life as the risk of contamination through leakage is removed.

The argument for upgrading to mechanical seals is pretty unequivocal. The questions remain: which mechanical seal should you buy, and who from? Which mechanical seal will depend on the requirements of each individual application. AESSeal, for example offers a range of standard inventory cartridge mechanical seals as well as a Standard Plus range, designed for specific pumps and pumping processes, or adapted to suit a customer’s individual needs.

For added reliability you could choose cartridge mechanical seals, which are pre-assembled, pressure tested and shipped as a unit. Cartridge construction eliminates the need to measure and set spring compression, and pre-assembly means seal faces are protected from damage during installation.

Who you purchase mechanical seals from is also matter of choice. But for industries governed by food contact materials (FCM) legislation there really should be only one option: from a supplier who can trace the origin of each component of every seal with absolute certainty. These companies must adhere to Regulation (EC) 1935/2004 on materials and articles intended to come into contact with food (also known as the Framework or FCM Regulation); and Regulation (EC) 2023/2006 on good manufacturing practices for materials and articles intended to come into contact with food (also known as the GMP Regulation).

Regulation (EC) 1935/2004 states: “A name, reference number and batch or delivery number should identify each raw material, so that it can be traced, if necessary. The traceability of raw materials is achieved throughout the production chain and in-house by the delivery and/or batch reference numbers.” Food and beverage is the most obvious industry that must comply with the regulations. But crossover between food and beverage and pharma-ceutical and bio pharma-ceutical sectors is routine – the use of the dairy by-product β-lactose as an excipient is a typical example. So regulations governing food contact materials (FCMs) must apply with equal weight in both sectors.

The supply chains involved in the production of component seals currently being imported into Europe from Asia are complex. In pursuit of low costs the product has often been through so many links in the supply chain that by the time it arrives at the end user all traceability has been lost. It seems incredible that any mechanical seal could contain, for example, antimony carbon, which looks like other harmless carbons but is, put simply, poisonous. Yet they have been seen on sites where the implications of it being misapplied could be disastrous.

Companies which have FCMs who fail to confirm the traceability of a mechanical seal are essentially building risk in to production processes at the same time as breaking the law. Is that a risk worth taking? Even for industries without FCM obligations, specifying a fully traceable mechanical seal is surely common sense – as well as a clear indication of their commitment to quality, reliability and fair practice. Pound for pound that’s got to be the surest measure of good value.

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