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Diamond Seals & Precision Cut

For small cross section O-rings and seals, the challenge can be the seal tolerance itself. When the O-ring tolerance is combined with the substrate tolerance, the resulting tolerance range for compression can be much bigger than desirable.   For example, a .070” (1.78mm) cross section O-ring, it requires a groove depth of .050±.002 (1.27±0.05 mm). In the ideal case, .018 to .022” (.46 to 0.56 mm) of the O-ring is compressed . Add to that any variation in plate gap, or increase the tolerance on the gland depth and we quickly run the risk of very low O-ring squeeze.

One solution is to increase the O-ring cross sectional thickness. Going from a .070” O-ring up to a .103” O-ring, the tolerance does not change. However, it is necessary to increase the groove width for proper fill to void ratio.

In the instances where increasing the O-ring size does not make up for the excessive tolerances on the hardware, or the gap between the plates, the next best option is a tall, slender seal. Both Diamond Seals and Precision Cut Seals can be can be tall and narrow compared to the round profile of an O-ring.

Diamond Seals are the molded option for a tall, narrow seal. We can add seal height without making the groove any wider. By adding seal height, the amount of compression on the seal increases, which may be enough for smaller ranges in groove depth tolerances. For example, if we swap a 0.070” (1.78mm) O-ring groove for a Diamond Seal groove of the same width (Diamond Seal height is 5.25mm), the groove deepens a bit and the the seal compression jumps from 0.020” (0.51mm) to .050” (1.25 mm). This increase may be enough to compensate for groove depth variation.   For more information on all advantages of a Diamond Seal.

For much larger groove depth variations, another sealing option is a rectangular profile Precision Cut. Precision Cuts are manufactured by the extrusion method, which allows for a high degree of size customization without the costly investment of a tool. The ability to make a very tall, thin seal can overcome a very wide tolerance range on the groove depth. For example, the illustration is for a seal cut length 24.50mm (0.965”) with 3mm (.118”) wall thickness. The tolerance on the seal in this instance is ± 0.51mm(0.020”), but on a traditional molded product of this size, would be closer to 0.20mm (0.008”). The height of the seal, coupled with the slightly reduced tolerance that comes with machining, results in favorable offset to excessive groove tolerances.

Parker Hannifin
O-Ring & Engineered Seals
2360 Palumbo Drive
Lexington, KY 40509
Ph: 859-269-2351
Fax: 859-335-5128