FEATURE BEARINGS, SEALS & GASKETS
Seeking cost-efficient mechanical seals? Look beyond the price tag...
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 quality customer service
I
t’s a common scenario across countless industries: downtime due to recurring
problems such as pump leakage or bearing failure brought about by a failed seal. 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,
32 DECEMBER/JANUARY 2021 | DESIGN SOLUTIONS
Above left: Seal optimising use of silicon carbide; Right: F range of cartridge seals supplied with FDA and EU compliant food safe materials
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.
UPGRADE TO MECHANICAL SEALS The argument for upgrading to mechanical seals is pretty unequivocal, but which mechanical seal should you buy, and who from? The type 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
Left: Example of a pump with perished gland packing
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
/ DESIGNSOLUTIONS
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
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
