Gap Seal Technical Info | GMN Bearing USA

Gap Seal Technical Info

Labyrinth Seal

Material: Polyacetal resin TK - AD; Delrin 100

Limits of use:

Temperature limits: - 40° C to 60° C/ - 40° F to 140° F

Speed limit: shaft speed 80m/ sec

Chemical resistance:

The acetaresin our seals are made of is resistant against a large variety of chemicals as: the most of the common organic solvents, alcohols, esters, ketones, aliphatic and aromatic hydrocarbons, greases and oils. Alkaloid water and base even at higher temperature do not harm the material.

On the other hand this material may not be used to seal against oxidators and organic and inorganic acids (pH < 4). Another advantage of this material is the very low value of water pickup (max. 0.8%).


Labyrinth Seal Labyrinth Seal


The GMN Gap Seal is mounted from two plastic parts, which create a zig zag shaped gap based on a conic envelope. Peaks and valleys of the inner and outer rings profiles (turned by the same tool) merge with each other so that they may be snapped together during the mounting process at GMN but are shipped as an inseparable unit.


Sealing principle: The basic principle of a labyrinth seal is based on the geometric shape of the labyrinth which causes some turns of the contaminant on its way to penetrate the seal. With the GMN Gap Seal the efficiency of the centrifugal force to accelerate the contaminant radially to throw it away from the sealing gap is increased by the conic envelope of the labyrinth. To penetrate the seal the contaminant has to overcome the centrifugal force by creeping from the larger labyrinth diameter facing the contaminant to the smaller diameter on the "dry" side of the seal. Particles penetrating the first steps of the conic labyrinth are expelled by the centrifugal force and led back to the side of the seal facing the contaminant.

There is no chance for a Gap Seal to protect against higher liquid levels and a pressure gradient between inside and outside of a Non-Contact Seal. Pressure gradients may be reduced or throttled but not sealed.

Protection against dust:

For this type of requirement the Gap Seal may be filled with grease before the mounting to increase the sealing efficiency against dusty environment. Please mark your order "pregreased". A certain amount of the grease may be moved out of the seal at rotating shaft.

The right mounting direction:

Care should be taken to install the Gap Seal the right way - the larger labyrinth diameter has to point to the contaminant.

Axial and radial clearance:

Axial and radial clearance of the seal are almost the same - approximately 0.5 mm. Both interfere each other.

Speed Limit

GMN Gap seals are pressed onto the shaft with a certain press fit. Due to centrifugal forces the inner ring could lift off of the shaft. The diagram below shows the speed limit depending on the size.

How to increase the sealing efficiency

Problem: The contaminant is splashing directly into the sealing gap.

Solution: One should use a disc in front of the seal with enough space between the seal and the disc to avoid backup of liquids in front of the sealing gap.

Problem: Heavy splashing liquids.

- There should be enough free space in front of the seal to allow free dropping or flowing of the splashing liquid.
- In addition one may use the "Sa Type" for rotating shafts or the "Si Type" for rotating housings.

Problem: Dual sealing function required

Solution: To keep the contaminant out of and the lubricant inside of the unit one may use two seals back to back (smaller labyrinth diameters of both seals facing each other). You should use a distance ring of at least 0.5 mm in between the seals. If heavy splashing liquids are expected, one may prepare drain hole located between both outer rings; in this case a minimum distance of 3 mm between both seals should be used.

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