What is Seal Compatibility in Filtration?

Seal compatibility refers to matching a filter element’s seal material (O-ring or gasket) to the hydraulic fluid in the system. The two most common materials are Nitrile (Buna-N/NBR) for petroleum-based fluids and Fluorocarbon (Viton/FKM) for synthetic fluids and high-temperature applications. Using the wrong seal causes swelling, hardening, or chemical failure.

Nitrile (Buna-N / NBR)

Nitrile is the most common hydraulic filter seal material. Compatible with petroleum-based hydraulic fluids, HLP/HM hydraulic oils, and most synthetic lubricants. Temperature range: -13°F to 250°F (-25°C to 121°C). NOT compatible with phosphate esters, Skydrol, ketones, or strong acids. If no seal material is specified on the element, it almost certainly uses Nitrile.

Fluorocarbon (Viton / FKM)

Fluorocarbon seals are required for aggressive fluids and high-temperature applications. Compatible with phosphate esters (Fyrquel, Skydrol), most synthetic fluids, and petroleum fluids at elevated temperatures. Temperature range: -4°F to 400°F (-20°C to 204°C). NOT compatible with ketones, some amines, or hot water. FKM seals typically cost 30–50% more than NBR.

Cross-Reference Seal Matching

When cross-referencing filters, seal material must match the original element or be compatible with the system fluid. Common manufacturer codes: B=Buna-N, V/H=Viton/FKM, E=EPDM, N=NBR. A filter with correct dimensions and micron rating but wrong seal material will leak or degrade, potentially contaminating the entire hydraulic system.

Reference Table

Seal Material	Temp Range	Petroleum Oils	Phosphate Esters	Water-Glycol
Nitrile (NBR)	-13°F to 250°F	Yes	No	Limited
Fluorocarbon (FKM)	-4°F to 400°F	Yes	Yes	No
EPDM	-40°F to 300°F	No	Yes	Yes
PTFE	-100°F to 500°F	Yes	Yes	Yes

Frequently Asked Questions

What seal material does my hydraulic filter need?

If your system uses standard petroleum-based hydraulic oil (the most common), Nitrile (Buna-N/NBR) seals are correct. If your system uses phosphate ester fluid (common in steam turbine EHC systems), you need Fluorocarbon (Viton/FKM) seals. Check your fluid data sheet if unsure.

What happens if I use the wrong seal material?

Using an incompatible seal material causes the seal to swell, harden, or dissolve. This leads to bypass leakage (unfiltered fluid reaching the system), seal debris contaminating the fluid, and potential damage to pumps and valves. NBR seals in phosphate ester fluid will fail within hours to days.

What do filter seal codes B, V, and E mean?

B or N = Buna-N/Nitrile (NBR), for petroleum-based fluids. V, H, or F = Viton/Fluorocarbon (FKM), for phosphate esters and high temperatures. E = EPDM, for water-based fluids. These codes appear at the end of many filter part numbers to identify the seal material.

Related Specifications

Filter Cross-Reference Filter Media Types Collapse Pressure

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