 |
Technical
Service Bulletin 94-4R1
|
Compression Gaskets: Their Function, Styles & Installation
A
compression seal is a means of preventing migration of liquids, gases
or solid contaminates across a joint or opening in an assembly or housing.
A seal not only prevents the escape of fluid from inside and foreign material
from entering the system from outside, but it must provide for easy installation
and removal.
The
majority of compression-type seal applications are static in nature. This
means the rigid components of the seal groove do not move in relation
to each other or to the seal. The only movement of the seal is caused
by vibration or internal fluid pressure.
In
service, the compressive force exerted by the gasket on the mating surfaces
insures a positive seal, even at low pressure. The flexibility of the
gasket material conforms to mating surfaces closing off the flow of fluid.
Figure
1 shows the gasket installed (A), compressed to form a seal (B) and under
pressure (C). As the systems pressure increases, the gasket moves to the
low pressure side of the groove and is supported by the groove wall. The
amount of pressure required to move the gasket within the groove is determined
by the frictional force of the seal material on the sealing surfaces.
Only when the systems pressure exceeds the frictional forces will the
seal seat itself on the low pressure side of the groove.
Under high pressure, the gasket acts just like a viscous fluid. Thus, due to the laws of fluid, the gasket transmits the systems pressure to all sealing surfaces including the low pressure side of the groove. In actuality, system pressure insures consistent gasket sealing.
Gaskets
require the sealing surfaces be finely finished so that the initial compressive
force can be applied until there is no clearance between the surfaces
and the gasket. Additional force is applied to compress the gasket material
to itself to achieve the required sealing pressures. This force is obtained
by tightening the filter per the installation instructions. Following
the recommended installation procedure is essential.
Figure 2 shows the basic types of filter designs and their gasket sealing arrangements. In applications where an element fits in a housing the filtering element may contain one or more gaskets which are integral parts of the element. This listing identifies the gaskets necessary to seal the filter assembly or which may require field replacement.
Figure 2
|
|
 |
| SPIN-ON OR SCREW-ON FILTER WITH SELF CONTAINED SEALING GASKETS: Amount of torque required for proper sealing varies with Filter design. Follow instruction supplied with each individual Filter. | TRAPPED SEAL FILTER: The bottom of the Filter housing fits into a groove in the Filter base where the gasket is contained. Torque Recommendations: 20-25 ft. lbs. |
 |
 |
| COVER SEAL FILTER HOUSING: Requires a gasket to seal the cover to the body when Filter element is replaced. Torque Recommendations: 10-15 ft. lbs. | BAND SEAL OR O-RING SEAL: Band seal housings may use an O-Ring gasket or an irregular shaped gasket. The gasket is compressed and sealed when the band is tightened. No torque recommendations can be given to cover all housings, but clamp and sealing flanges must be kept in good condition. |
 |
 |
| LIP SEAL FILTER HOUSING: The bottom of the Filter housing is provided with a turned lip which contacts a gasket contained in a recess in the Filter base. Torque Recommendations: 15-20 ft. lbs. | BOLT FLANGE SEALED FILTERS: The gasket is held securely between the flange at the top of the housing and Filter cover by screws or bolts. Torque Recommendations: 20-25 ft. lbs. |
For additional information, contact:
Filter Manufacturers
Council
P.O. Box 13966
Research Triangle Park, NC 27709-3966
Phone: 919/406-8817 Fax: 919/406-1306
www.filtercouncil.org
Administered by Motor & Equipment
Manufacturers Association
Created May 1996
Back to Top
Back to Technical Service Bulletins