WTL – Seal of approval
March 04th 2008 The addition of mechanical seals to the Water Technology List (WTL) has again focused attention on the potential for water savings in this area. Here, John Crane Safematic’s commercial manager Jussi Sorvoja examines how modern technology is helping realize some of that potential
The idea of reducing the water used to quench and lubricate mechanical seals is by no means new. However coupled with increasing concern for the environment, the addition of mechanical seals to the WTL is making this an area that is now being taken far more seriously than it has been. There have been numerous attempts made in the past to reduce the volume of water that is continuously fed to the seal faces, but attention is now focusing to the smarter solutions to this problem that have been made possible by recent developments in technology.
One such approach that has emerged in recent times is the use of an ‘intelligent’ control system that supplies water to the seal only as and when it is actually required.
Regulating the volume of water fed to the seal so that it matches the heat load placed on the system in this way can produce some dramatic water consumption reductions and this allows this type of unit to provide a highly-effective, reliable and economical way to combine optimum seal performance with significantly reduced costs.
Like all the best ideas, the essence of these units is very simple. The secret lies in a spring which is fabricated from a special heat-activated shape-memory alloy. The heat-sensitivity of the spring allows it to expand and contract in response to changes in temperature, and as it does so it opens and closes the channel through which water flows to the actual seal. By allowing the water to flow only when it is needed rather than continuously, this type of unit can produce impressive reductions in seal water consumption of up to 97%. It’s easy to see why this solution is growing rapidly in popularity and with water management equipment now eligible for tax relief via the Enhanced Capital Allowance scheme that growth looks set to accelerate in pace in the future.
Reducing the amount of water used automatically reduces the water bill which follows but there are also other significant cost savings to be enjoyed from this type of unit The water used to cool and lubricate the seal must be filtered before use to prevent contaminants from damaging the seal faces, and then it usually needs to be treated prior to disposal in order to prevent environmental contamination. Cutting water consumption immediately cuts any costs associated with these filtration and treatment processes.
Because these units operate in response to fluctuating conditions within the seal they are usually able to adapt automatically to different pressure and temperature conditions and this flexibility makes them ideal for many different types of application. In addition, the better versions are also very simple to install as they need no wiring or electrical supply, and they are also virtually maintenance free, requiring only an occasional check on the integral filter to ensure that it is operating efficiently. They also normally incorporate a fail-safe mechanism that prevents seal failure in the event of a fault developing.
There is a growing recognition of the potential that this sort of intelligent control system offers. Indeed a project using just this type of unit that recently won a prestigious Business Enterprise Award - Best Specific Environmental Initiative - from the United Nations Association of Australia where there is perhaps a greater imperative to save water than in many other locations.
And with applications that go beyond just pumps – the units can be used to dissipate heat from bearing coolers, cooling jackets and similar items of equipment – they surely point the way ahead for anyone looking for savings on their mechanical seal water usage. John Crane is part of the Smiths Group. | 
