One of the most effective ways of sealing rotating shafts is by mechanical seals. These consist of two plane faces arranged perpendicular to the axis of the rotating shaft (which gives rise to the alternative name, "radial face seal"). One face is fixed to the equipment casing or vessel, while the other is fixed to the shaft and so rotates with it. Frictional heat generation and wear are controlled by maintaining a film of lubricant between the seal faces. As such, mechanical seals resemble thrust bearings.
Mechanical seals have replaced packings as the seal of choice in many applications, primarily because mechanical seals offer:
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reduced wear (from lower friction) |
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reduced heat generation (from lower friction) |
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lower energy consumption (from lower friction) |
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reduced maintenance requirement (from reduced wear) |
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tighter control of shaft leakage (from extremely low or zero fluid emissions) |
Mechanical seals are precision devices, requiring in general more careful installation and higher initial investment than those of soft packings.
See ... List of Division Members
ATEX Directive 94/9/EC
The ATEX Directive (also known as "ATEX 95") -
‘Equipment and Protective Systems intended for use in potentially explosive
atmospheres’ - has been mandatory since 2003 July 1.
Despite this, the interpretation of how this Directive applies to mechanical seals
is still largely misunderstood. Consequently, the Members of the ESA Mechanical Seals
Division have developed a Position Statement to act as a
guidance towards clarification.
To download (as a pdf file) please click .. ESA ATEX Position Statement
Sealing Technology BAT guidance note
Sealing technology is involved in virtually all of the sectors covered by the EU IPPC
Directive. Yet, only limited information and guidance on sealing options is
available in most of the BREF notes which have been published. For this reason, the ESA
has published a Sealing Technology BAT
guidance note, with sections covering the best available
techniques for sealing solutions required to meet the IPPC legislation.
Seal Forum
This document is a compilation of technical papers from leading
rotating equipment engineers across the globe, providing a balanced view of
mechanically-sealed and sealless systems in a wide range of applications. The user experts
give unbiased reports about their own experience with the various options available for
rotating equipment. This is a "must read" for all rotating equipment
users!
For more information, please see Seal Forum
The document is a joint ESA+FSA publication, available in English and German language versions.
Other documents
Member Companies have an ongoing commitment to research and
development. This has resulted in the continually increasing performance of mechanical
seals, reflecting state-of-the-art technology which has been used in the design of seals
available in the marketplace today. In anticipation of increasing environmental
regulations, new generations of mechanical seal products have been developed to provide
cost-effective solutions for the control of emissions. Increased life of 3+ years has been
attained reliably with low emission single seals and dual seals. These results have been
obtained through the use of improved designs, high quality face materials, attention to
manufacturing and assembly details, and enhanced seal chamber environment. These advances
in seal technology go hand in hand with improved installation, maintenance and operating
procedures, to enable considerable reductions in fugitive emissions and hence substantial
savings for the operator.
Most of today's low emission single mechanical seals, using modern materials and advanced technology, are performing reliably with emissions typically below 1g/h under normal operating conditions in the field.
Emission from today's dual mechanical seals with barrier fluids is essentially zero, usually described as "not measurable with existing instrument technology". These seal arrangements can provide very tight emission control, meeting the requirements of the most stringent environmental legislation world-wide. These performance levels have been supported by independent users over extended periods of operation in the field.
In recognition of these developments, the Mechanical Seals Division has prepared a document to provide information and guidance on:
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performance of modern, low emission mechanical seals |
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application recommendations |
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achievement of environmental legislative requirements |
This document is for use by original equipment manufacturers, engineering contractors and end users in the process industries. It is entitled, "Meeting emission legislation requirements with today's advanced technology mechanical seal systems"(ESA Publication No. 005/95).
The publication is also available in French and German language versions.
Although much of this 1995 document continues to be relevant to current practice in mechanical sealing, the Sealing Technology BAT guidance note (mentioned above) covers the same subject and, in addition, brings the topic up to date. Consequently, the BAT guidance note should be used as the primary document when considering the latest technology options for managing fugitive emissions in mechanical seals.
Recommendations for safe shaft sealing from ESA Publication No. 005/95:
| Area | Leak rate maximum (g/h) | Specific gravity of process fluid | Acceptable sealing solution |
| 1 | 2.5 - 24 | >0.4 | -
general purpose single seals |
| 2 | 0.5 – 2.5 | >0.5 – 0.7 | - advanced
technology single seals - dual unpressurised (tandem) seals - dual pressurised (double) seals |
| 3 | <0.5 | >0.4 | - advanced
technology single seals vented to a closed vent system - dual unpressurised (tandem) seals vented to a closed vent system - dual pressurised (double) seals |
| <0.4 | - dual pressurised (double) seals |
Pressure Equipment Directive
97/23/EC
The Directive will have significant implications on sealing technology,
which is of course used extensively for the reliable and safe containment of fluids under
high pressure. In response, the Mechanical Seals Division of the ESA has developed a Position Statement, to act as guidance
about the legislation and its relevance to sealing systems.
