Specialty Compound for EP Gear Oils & ATF
Polyacrylate (ACM) is the specialty oil seal compound for extreme-pressure (EP) gear oils, automatic transmission fluid (ATF), and hot petroleum oils that swell NBR and don't require the cost of Viton. Rated -25°F to 300°F with superior abrasion resistance to NBR. 17 Durus sizes stocked.
What Is a Polyacrylate Oil Seal?
Polyacrylate (ACM) is an acrylic-based elastomer engineered specifically for petroleum oils and EP-additive lubricants. While NBR has good general oil resistance, modern EP gear oils contain sulfur and phosphorus additives that aggressively attack NBR. Polyacrylate is chemically resistant to these additives, providing extended service life in applications where NBR would degrade prematurely.
ACM seals fill the temperature gap between NBR (max 250°F) and Viton (max 400°F) - operating reliably up to 300°F continuous at a cost typically 2-3× NBR rather than 4-6× for Viton. The compound also has superior abrasion resistance compared to NBR, making it the preferred choice for shafts with marginal surface finish or slight runout issues.
When to Specify Polyacrylate
- EP gear oils (GL-5) - The sulfur/phosphorus additives in extreme-pressure gear oils attack NBR; ACM resists
- Automatic transmission fluid (ATF) - ATF additives are aggressive to NBR; ACM provides longer service
- Hot petroleum oils 250°F - 300°F - Above NBR's limit but below where Viton is required
- Manual transmissions and differentials - Standard application where EP gear oil is specified
- Shafts with marginal surface finish - ACM's abrasion resistance handles slight roughness better than NBR
When NOT to Use Polyacrylate
- Water, steam, water-glycol coolants - ACM has poor water resistance; use NBR or specialty compound
- Brake fluid - Glycol-ether brake fluids attack ACM; use Viton
- Below -25°F - ACM stiffens at low temperatures; use NBR or silicone
- Fuels and aromatic chemicals - Use Viton for fuel exposure
Material Comparison
| Compound | EP Gear Oil | ATF | Hot Oil >250°F | Cost vs NBR |
|---|---|---|---|---|
| NBR | Fair | Poor | Poor | 1× |
| Polyacrylate (ACM) | Excellent | Excellent | Excellent | 2-3× |
| Viton (FKM) | Excellent | Excellent | Excellent | 4-6× |
Polyacrylate hits the sweet spot for gear oil applications: significantly better than NBR for EP fluids and hot oil, at roughly half the cost of Viton. For the specific use cases above, ACM is the cost-optimal choice.
Identifying Polyacrylate Parts
Durus polyacrylate oil seals are identified by a P suffix in the part number type code - examples: 187263 SBP (SB2 type, Polyacrylate), 155315 BWYP, 262457 B5YP. The product description and spec metafield explicitly state "Polyacrylate (ACM)" as the material.
Related Materials
Frequently Asked Questions
What is the difference between Polyacrylate and Nitrile (NBR) oil seals?
Polyacrylate (ACM) is specifically engineered for EP gear oils, automatic transmission fluid, and hot petroleum oils - applications where the sulfur and phosphorus additives in modern EP lubricants attack standard NBR rubber. ACM also extends the operating temperature range from NBR's 250°F limit up to 300°F, with superior abrasion resistance to NBR. ACM costs 2-3× NBR. For applications using standard mineral oils below 250°F, NBR remains cost-effective. For EP gear oils or temperatures above 250°F, specify ACM.
Are Polyacrylate oil seals more expensive than Viton?
No - Polyacrylate is typically half the cost of Viton. Polyacrylate costs roughly 2-3× NBR; Viton costs 4-6× NBR. For applications within ACM's capability (EP gear oils, ATF, hot petroleum oils up to 300°F), Polyacrylate provides equivalent performance to Viton at meaningfully lower cost. Reserve Viton for the higher-temperature applications (above 300°F), fuels, and aggressive chemicals that exceed ACM's range.
Can Polyacrylate oil seals handle water or steam?
No. Polyacrylate has poor water resistance and will degrade in continuous water or steam service. For water-glycol coolants, hot water, or steam applications, specify NBR (Buna-N) for cool water service or a specialty water-rated compound for hot water. Polyacrylate is exclusively for petroleum oil applications. Specifying ACM for a water-based fluid leads to rapid seal failure.
What gear oil applications require Polyacrylate seals?
Modern API GL-5 extreme-pressure (EP) gear oils contain sulfur and phosphorus additives that provide load-carrying capacity for hypoid gears and heavily loaded gearboxes - but these additives attack standard NBR seal lips. Polyacrylate is the recommended compound for: automotive rear axle differentials, manual transmissions running GL-5 oil, industrial gearboxes with EP additives, automatic transmissions (ATF service), and any application where the lubricant manufacturer recommends ACM seals.
How do I know if my seal is Polyacrylate?
Three indicators: 1) The Durus part number includes a "P" suffix in the type code - examples include SBP, B5YP, BWYP, BZP. 2) The product description and material metafield explicitly state "Polyacrylate (ACM)". 3) The spec sheet or original equipment manual specifies ACM for the seal position. If the equipment uses EP gear oil or ATF, the original seal was likely ACM and the replacement should match. Confirm with Texas Belting at (888) 203-2358 if uncertain.
Cross-reference from any CR, SKF, National, Federal-Mogul, or Timken part number. Houston, TX warehouse stocks the full Durus catalog with same-day shipping for in-stock items.
Call (888) 203-2358 or email sales@texasbelting.com with your existing part number, equipment make/model, or shaft and bore measurements.
