If I had to estimate the number of times someone asked for a seal meeting AMS7287, the answer is very few. On the other hand, the number of times someone has asked for a seal material meeting Mil-R-83485, AMS-R-83485, MS83485 or AS83485 it would be too many to count. The lack of inquiries surrounding AMS7287 is surprising, given the document has been active since 2012. Therefore, if you are reading this blog and are familiar with the AMS-R-83485 specification, but do not know much about the AMS7287 specification you are not alone! This blog is intended to explain the differences and help you understand one specification with respect to the other.
But first, let me provide the title and status of each document as of April 2021:
|Number||Title||Status & Rationale||Part Drawing & Numbering System|
|Mil-R-83485||Rubber, Fluorocarbon Elastomer, Improved Performance at Low Temperature/td>||Cancelled, S/S by AMS-R-83485||Mil-R-83485/1 M83485/1-xxx|
|AMS-R-83485||Rubber, Fluorocarbon Elastomer, Improved Performance at Low Temperature||Cancelled May 2014, S/S by AMS7287 (Ty I O-rings) AMS3384 (Ty 2 Molded parts)||Mil-R-83485/1 M83485/1-xxx|
|AMS7287||Fluorocarbon Elastomer (FKM) High Temperature / HTS Oil Resistant / Fuel Resistant Low Compression Set / 70 to 80 Hardness, Low Temperature Tg -22F (-30C) For Seals in Oil / Fuel / Specific Hydraulic Systems||Active; Issued 2012-08||AS83485A M83485/1-xxx|
Looking at both Mil-R-83485 and AMS-R-83485, the document was largely unchanged in both requirements and intent. Qualification requirements included limits for:
Basic physical properties
TR-10 (Temperature Retraction) of -20°F
Compression set for 70 hours @ 75°F
Compression set for 22 hours @ 392°F
Dry Heat age of 70 hours in 528F air for a change in physical properties and weight.
Fluid Immersion in Fuel, 70 hours at 73°F for a change in physical properties and volume
*Long term Compression set for 166 hours @347°F (with the second set to cool for 18 hours in test fixture)
*Fluid Immersion in Di-ester polyol, 70 hours at 347°F for compression set plus a change in physical properties and volume
(*not carried over to AMS7287)
Over the years of “83485” revisions, there were some changes in the exact fluid called out, but the intent did not change. For example, TT-S-735 Type III was later updated to Fuel B which might appear to be a change, but both are a 70/30 blend of isooctane and toluene. Similarly, the Stauffer Blend 7700, a di-ester polyol synthetic-based oil, was updated to AMS 3021 (also known as Hatco 7700 and Service Fluid 101) which is basically the Mil-L-7808 oil, also a polyol synthetic-based oil.
An interesting detail about the specifications has to do with ownership and the subsequent naming convention. The documents with the ‘Mil’ prefix were owned by Wright Patterson Air Force Base, and when they turned ownership over to SAE, the document number prefix transitioned to “AMS”. This naming convention also explains why some of the fluids within the specification switched from a brand of di-ester polyol to a reference oil with an AMS prefix.
The change to AMS7287 brought about more than a few changes to nomenclature and standardization of fluids. The testing criteria which stayed the same are the first six listed above for Mil-R and AMS-R-83485. The polyol oil immersion from the requirements was carried over, however, there is a difference to the fluid, the testing limits, and the addition of a compression set. The synthetic oil was updated to AMS3085, which is a reference lubricant for High Thermal Stability (HTS) oils such as Mil-PRF-36699(HTS), Mil-PRF-7808 Grade 4 and AS5780 Class HPC. This change makes sense given the widespread use of AMS-R-83485 seals in HTS oil applications such as gear turbine oils and engine oils. In addition, the AMS3085 type oil is standard among other SAE-owned specifications, such as AMS7257 and AMS7379.
Further technical changes from AMS-R-83485 to AMS7287 are the addition of the following requirements:
Glass transition temperature (Tg) of -20°F
Long Term Compression set for 336 hours @ 392°F
You may notice that the original list of requirements at the beginning includes a 166-hour compression set but at a more modest temperature of 347°F, with a maximum result of 25% on O-rings. The addition of a 366-hour test at a temperature 45°F higher is significant. Qualified materials must not exceed a compression set of 50%. This more aggressive condition could easily cause a material that meets the requirements of AMS-R-83485 not to meet the requirements of AMS7287.
Another area of change is with respect to conformance testing. The “83485” specifications require O-rings to undergo acceptance testing on size -214 O-rings molded at the same time as the production batch of O-rings. The move to AMS7287 requires testing on the actual O-rings unless they are an unsuitable test size. In the case of unsuitably sized O-rings, only then would the -214 O-rings be tested for physical properties and compression set.
The final area of significant change in AMS7287 is the requirement of each manufacturer to have their material approved and listed on the Qualified Producers List (QPL). This means each manufacturer must also be approved and listed on the Qualified Manufacturer’s List (QML). QML and QPL status require a robust quality system and rigorous audits by the governing body, which ensure both the material and the necessary manufacturing practices comply with the AMS7287 standard.
Parker’s VM125-75 fluorocarbon meets all the requirements of AMS7287. For more information on VM125 or the AMS7287 specification, please reach out to one of our Application Engineers, or click here to view test data and our product bulletin.
Article contributed by Dorothy Kern, applications engineering lead, Parker O-Ring & Engineered Seals Division
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