Shaft End Seals

By appropriate notation, the vendor may be requested to offer alternatives for the specific application, if a particular type of seal has not been selected at the time of the specification writing. It is very difficult to generalize the seal selection, because of the many requirements and numerous methods available. For specification purposes, the single most important factor to pass on to the vendor is the requirement for a positive seal, which would be a mechanical contact of the oil buffered or dry gas type or oil film seal. All other types have significant process gas leakage associated, which can be controlled if required, but at best cannot be considered in the positive class. For oil buffered seals, a quantity of acceptable inner leakage should be established for use later at test time. In the inquiry phase, it can be given as a target value for vendor comment or acceptance or as a requested value from the vendor, which would then be made a contract value for the order specification.

Seals, particularly the restricted leakage type, require auxiliary piping, control valves, and other items. If more than a suggested schematic is to be included in the vendor's scope of supply, a statement to that effect should be made. For the oil buffered systems, if a separate oil system is required, this must be stated, and it can be detailed in the accessory section with the lube system. For dry gas seals, the type of support system must be specified. The vendor's proposal should be requested to outline materials and to permit user review of the standard materials for compatibility. As always, if a problem is known to exist or is suspected, acceptable materials may be specified. The vendor can use the list to review his ability to conform or to propose alternatives. This method tends to save some time.

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