For many engineers with responsibility for pumps and other rotating equipment, mechanical seals can appear to be complex products, perhaps too difficult to be bother with. Some will simply stick with tried and tested, though inefficient, methods of sealing leaking pumps such as gland packing.

The following has been written to change this perception, to explain hew advances in sealing technology have resulted in a new generation of seals which are highly cost effective, reliable, easy to fit and require little or no maintenance.

So for those of you who have responsibilities for specifying sealing systems we hope the following will be of value as an outline guide to the many valuable advantages to be gained from fitting mechanical seals.

Why Mechanical Seals?

Pumps and vessels handling liquids all need some form of shaft sealing device to prevent the liquid leaking uncontrollably from the equipment. Traditionally both pumps and vessels with rotating shafts have a gland or 'stuffing box' to accommodate the sealing device.

The Problems Posed By Gland Packing.

Gland packing is a well used, traditional method of sealing. Far from perfect, it relies on the gland being allowed to leak in order to provide lubrication under the gland packing and thus prevent overheating and excessive wear of both the packing and, more importantly, the shaft. Once installed the gland packing has to 'bed in'. This necessitates frequent small adjustments until the required level of leakage is achieved. When the packing has been fully 'bedded in' regular adjustments are still needed to maintain this required leakage.

Product Down The Drain.

A correctly adjusted gland packing with a steady drip leakage will leak at an average of 13 litres a day (normal rates for water leakage). That's 4745 litres per year - straight down the drain. This may be acceptable to some plant operators but what if the product is expensive ? Or what if it is dirty and has to be cleaned away or requires special effluent treatment?

Which ever way you look at it this leakage is extremely wasteful and environmentally unacceptable.

Cost Maintenance.

The majority of packed glands required adjustment 2 or 3 times a month. Repacking is usually needed at least twice a year. even if a gland has been correctly maintained the shaft will eventually become worn and need replacing.

The cost of correctly maintaining a packed gland can typically be in excess of £300 per year when taking labour costs, downtime and replacement packing into account. Even higher if a pump is remotely located as so often is the case in the water industry. And when the shaft does need to be replaced this cost will escalate dramatically.

Saving On Leakage, Wear And Power.

One of the simplest and most popular types of mechanical seal is the formed metal bellows seal. Leakage from this type of mechanical seal is so small that is usually undetectable. A tremendous benefit when handling expensive or dirty liquids.

Mechanical seals require minimal attention to maintain an effective seal. No wear of the equipment takes place when seals are fitted. What's more the absorption of power is significantly reduced when compared with gland packing. On a typical water application at a pressure of 10 bar a mechanical seal absorbs approximately 85% less power than gland packing. This represents a cost saving of several hundred pounds per year on a pump running continuously.

Correct seal selection needs experience and applications knowledge to ensure that the best possible selection is made. Our extensive knowledge base of applications, materials, liquids and sealing solutions has been accumulated through many years of experience. This knowledge base enables us to provide users with the best seal recommendation for safe and reliable performance.