Hydraulic fluid compatibility chart for different seal materials

In all hydraulic systems, whether in industrial machinery or agricultural tractors, seal material compatibility with hydraulic fluid is a must. Sealing the compatibility of the material with the hydraulic fluid is a crucial element in the design and maintenance. As hydraulic fluids transfer power, seals ensure protection. If they are not compatible, it can result in leakage and premature wear, as well as contamination, or a catastrophic system failure.

Understanding how various seal materials work with different hydraulic fluids is vital for maintenance teams, engineers, and system designers. This guide will explain the basic principles of compatibility and provide an actual compatibility chart and guidance on how to select the best materials for sealing your needs.

Why hydraulic fluid compatibility matters?

Hydraulic seals are constantly exposed to fluids under pressure, temperature fluctuations, and dynamic movements. If incompatibility is a problem, many failure mechanisms can be triggered:

• Shrinkage or swelling of seals
• Softening or hardening of Elastomers
• Cracking, blistering, or degradation
• Performance loss due to sealing and leakage
• The contamination of hydraulic fluid

These problems arise due to physical and chemical interactions between the polymer and the fluid material.

For instance, nitrile Rubber (NBR) is a good choice for mineral oils, but it can break down quickly when exposed to phosphate esters. The wrong combination could cut down the seal's life significantly.

Common hydraulic fluids

Before you dive into seal materials, it's essential to comprehend the primary kinds of hydraulic fluids:

1. Mineral oil-based fluids

• Most commonly utilized (e.g., HLP oils)
• Derived from petroleum
• Compatible with a variety of Elastomers

2. Synthetic fluids

• Incorporates the PAO (polyalphaolefin) along with esters
• Provide better stability in temperature and biodegradability

3. Water-based fluids

• Solutions for water-glycol
• Useful for protection against fire
• Require special seal materials

4. Phosphate ester fluids

• Fluids with fire-resistance are commonly used in the steel and aviation industries.
• Chemically aggressive towards several Elastomers

5. Biodegradable fluids

• Organic oils, synthetic esters, or vegetable oils
• More environmentally friendly, but chemically reactive

Every type of fluid has a different way of working with seals, which makes compatibility charts crucial.

Common hydraulic seal materials

1. NBR (nitrile rubber)

• The most commonly utilized elastomer
• Great resistance to the petroleum-based oils. Excellent resistance to petroleum-based
• Good mechanical properties
• A limited resistivity to water-based substances as well as esters

2. FKM (fluoroelastomer / viton)

• Resistance to high temperatures
• Good compatibility with a variety of synthetic fluids and oils.
• Resistant to the phosphate ester (in several instances)

3. EPDM (ethylene propylene diene monomer)

• Great for water-based fluids
• Incompatible with mineral oils

4. PTFE (polytetrafluoroethylene)

• Chemically inert
• Compatible with virtually all hydraulic fluids
• The friction is low, but there is a limited amount of elastic

5. FFKM (perfluoroelastomer)

• Premium material with a near-universal chemical resistance
• For extreme conditions, it is suitable.
• High cost

6. Silicone

• Large temperature range
• Mechanical strength is limited, and it's not compatible with hydraulics

Hydraulic fluid compatibility chart

Here is an easy, practical compatibility chart based upon information from the industry:

This table provides general trends in compatibility that are observed for hydraulic applications.

Understanding compatibility ratings

Compatibility charts typically make use of the following scores:

• Excellent/good - Not a significant impact recommended for long-term use
• Limited changes in the appearance or quality. Be aware of this.
• Poor / not recommended - Severe degradation likely

It is important to keep in mind that compatibility is affected by:

• Temperature
• Pressure
• Fluid additives
• Time to expose

Even a "good" combination may fail under the most extreme of conditions.

How different fluids affect seal materials

Mineral oil effects

Mineral oils are typically compatible and compatible with the NBR as well as FKM, which makes them the standard choice for the majority of systems. However, the addition of anti-wear agents may affect the long-term performance of the product.

Water-glycol fluids

These fluids have a significant amount of water. This can lead to hydrolysis in many elastomers.

• Best-suited material: EPDM
• Bad selections: NBR and FKM

Phosphate ester fluids

These are abrasive fluids that are used in fire-resistant systems.

• Suitable materials: FKM, FFKM, PTFE
• Not suitable: NBR and many standard Elastomers

Synthetic esters

These biodegradable fluids are polar and may cause swelling in elastomers.

• Recommended: FKM, PTFE
• Caution: NBR

Biodegradable oils

The environment is friendly, yet the chemicals are active.

• Preferred: FKM, PTFE
• Compatible with limited limitations: NBR

Key factors when selecting seal materials

The selection of the appropriate seal material requires more than simply fluid compatibility. Take into consideration these aspects:

1. Temperature range

Every material has an established operating temperature. For instance:

• NBR: up to ~120 °C
• FKM: up to ~200 °C
• PTFE: up to ~260 °C

The high temperatures speed up chemical reactions and destruction.

2. Pressure and mechanical load

Hydraulic systems typically operate under high pressures. Materials such as PTFE need backup rings due to their lack of elasticity.

3. Chemical additives

The fluids of hydraulic contain certain additives, such as:

• Anti-wear agents
• Anti-corrosion agents
• Oxidation stabilizers

These could significantly impact compatibility.

4. Dynamic vs static applications

• Flexible seals require elasticity and wear resistance
• Static seals prioritize resistance to chemicals

For instance:

• NBR is very effective in dynamic systems.
• PTFE excels in high-chemical and static environments.

5. Cost vs performance

• NBR: affordable and widely utilized
• FKM: mid-range cost, greater performance
• FFKM is a top option for critical systems

Practical selection guidelines

Here's a brief guide for selecting seal materials:

• For normal hydraulics (mineral oil):
  Use FKM or NBR
• For systems with high temperatures:
  - Utilize PTFE or FKM
• Water-based liquids
  The use of EPDM
• For phosphate esters that are fire-resistant:
  - Make use of FKM FFKM as well as PTFE.
• For chemicals that are highly aggressive or hazardous in environments:
  - Use FFKM

Common compatibility mistakes

Even experts make mistakes in selecting the seal materials. These are the most common mistakes:

1. Assuming all Oils are the same

Different hydraulic oils, even having the same viscosity, may contain various chemical components.

2. Ignoring additives

The addition of additives can significantly alter the way that compatibility is exhibited.

3. Overlooking temperature effects

A material that is compatible with ambient temperatures can fail when exposed to higher temperatures.

4. Mixing fluids

Mixing fluids can trigger unexpected chemical reactions, as well as compatibility issues.

Testing and validation

Compatibility charts are merely guidelines, not guarantees. The best practices are:

• Testing of seal materials in the laboratory using actual fluid
• Reviewing Material Safety Data Sheets (MSDS)
• Manufacturers of consulting seals
• Conducting field tests

The industry standard suggests that testing in the real world is crucial since performance is dependent on operational conditions.

Future trends in seal compatibility

Hydraulics is changing and is facing new challenges:

• More frequent utilization of biodegradable fluids
• Pressures and operating temperatures are higher.
• The demand to have more frequent service periods

These patterns are driving innovations in:

• Advanced Elastomers
• Composite materials
• Improved PTFE blends

Fluid compatibility between hydraulic and seals is not only an engineering issue, but it is a vital aspect of the reliability, safety, and effectiveness. If the wrong combination is used, it can cause rapid failure of the seal as well as costly downtime, and even a hazard to safety.

A well-informed process of selection should be able to consider:

• Fluid type
• Properties of material
• Operating conditions
• Balance of cost-performance

While compatibility charts can be an effective starting point, they should be supplemented by tests and guidance from the manufacturer.

If you know what happens when hydraulic fluids come into contact with seals, you can greatly improve the performance of your system, prolong the lifespan of your components, and cut down on the cost of maintenance.