PolyPak Seal: Complete Guide to Structure, Materials and Selection

What Is a PolyPak Seal

A PolyPak seal is a composite hydraulic seal consisting of:

• A polyurethane (PU) sealing lip
• An elastomer O-ring energizer (NBR or FKM)

It is widely used in hydraulic cylinders for both rod sealing and piston sealing applications.

In engineering terms, it is also called:

• O-ring energized lip seal
• Composite hydraulic seal

PolyPak Seal Structure & Working Principle

Structure

A typical PolyPak seal includes:

• Outer sealing element: PU lip
• Inner energizer: O-ring (NBR / FKM)

Working Principle

The sealing mechanism combines two effects:

1. Initial sealing force

    → Provided by the O-ring (preload)

2. Pressure-activated sealing

    → Hydraulic pressure pushes the lip outward

    → Increases contact force automatically

Result:

• Excellent sealing at low pressure + high pressure

• Stable performance under dynamic conditions

PolyPak Seal Materials

1. Sealing Lip Materials

Polyurethane (PU)

• Excellent wear resistance
• High extrusion resistance
• Suitable for hydraulic systems

Widely used in:

• Construction machinery
• Injection molding machines

2. O-Ring Energizer Materials

NBR (Nitrile Rubber)

• Cost-effective
• Suitable for mineral oil

FKM (Viton)

• High temperature resistance
• Better chemical resistance

3. Advanced Material Options

For demanding applications:

• PTFE filled compounds
• High-performance elastomers

Used in:

• High-speed systems

• Aggressive media environments

PolyPak Seals vs Other Hydraulic Seals

PolyPak Seal vs U-Cup

PolyPak Seal vs O-Ring

PolyPak Seal vs Step Seal

Applications of PolyPak Seals

PolyPak seals are widely used in:

Hydraulic Equipment

• Hydraulic cylinders
• Pumps and valves

Industrial Machinery

• Injection molding machines
• Press systems

Heavy Equipment

• Excavators

• Mining equipment

How to Select the Right PolyPak Seal

Selecting the correct seal requires evaluating:

1. Pressure

• Typical range: up to 35 MPa

2. Temperature

• PU + NBR: approx. -30°C to +100°C
• PU + FKM: higher temperature capability

3. Speed

• Typical: ≤ 0.5 m/s

4. Media

• Mineral oil
• Hydraulic fluids

5. Installation Space

• Groove size

• Clearance

PolyPak Seal Sizes & Standards

Common standards include:

• Parker BA profile
• Metric and inch sizes

Equivalent designs are widely available for replacement applications.

Common Problems and Solutions

Leakage at low pressure

• Cause: insufficient preload
• Solution: select proper O-ring hardness

Excessive wear

• Cause: poor lubrication or contamination
• Solution: improve surface finish and filtration

Extrusion damage

• Cause: high pressure + large clearance

• Solution: use harder PU or add backup ring

FAQ

Q: What is the difference between PolyPak and Poly Seal?

A: "Poly seal” is a non-standard term.

In most cases, it refers to PolyPak seals or polyurethane seals.

Q: Can PolyPak seals be used for piston applications?

A: Yes.

PolyPak seals can be used for both rod and piston sealing.

Q: What materials are used in PolyPak seals?

A: Typical combination:

PU (sealing lip)

NBR or FKM (O-ring energizer)

Q: Are PolyPak seals suitable for high pressure?

A: Yes.

They perform well in medium to high-pressure hydraulic systems.

Need PolyPak Seal Replacement or Custom Design?

We provide:

• Standard and custom PolyPak seals
• Parker equivalent profiles
• Material customization (PU, NBR, FKM, PTFE)
• Fast delivery for global B2B customers

Contact us for technical support or quotation.

Email: xhh@xhh-smartech.com