What is a DAs Seal?

A DAs seal (also written as D‑A‑S, DA‑S, or DAs) is a compact, double-acting piston seal assembly designed for hydraulic systems. Combining sealing, guidance, and backup functions into a single unit, it ensures reliable bidirectional sealing under high-pressure conditions. This guide explores its construction, materials, applications, and advantages, providing a comprehensive understanding of this critical hydraulic component.

Definition & Core Functionality

The D‑A‑S seal integrates five components into one compact assembly:

1. A nitrile rubber (NBR) sealing ring for dynamic and static sealing.
2. Two polyester elastomer backup rings to prevent extrusion.
3. Two polyacetal (POM) guide rings for piston alignment and wear protection.

This unified design eliminates the need for separate backup or guide rings, simplifying installation and reducing inventory complexity. It operates under pressures up to 31.5 MPa (≈ 315 bar) and temperatures ranging from –30°C to +100°C, making it ideal for demanding hydraulic applications.

Construction & Components

The DAs seal’s efficiency stems from its multi-material, multi-functional structure:

1. Profile Seal Ring (NBR)

• Material: Nitrile rubber (70 ShA hardness), compatible with mineral oil-based hydraulic fluids.
• Role: Provides primary sealing by maintaining contact with the cylinder bore during piston movement.

2. Backup Rings (Polyester Elastomer)

• Material: High-performance polyester elastomer.
• Role: Flanks the sealing ring on both sides to prevent elastomer extrusion into clearance gaps, even under extreme pressure.

3. Guide Rings (POM)

• Material: Polyacetal (POM), known for low friction and wear resistance.
• Role: Centers the piston within the bore, absorbs side loads, and protects the sealing lip from abrasion.

This “compact seal” design allows snap-in installation into closed or split grooves, minimizing machining costs and assembly time.

Technical Specifications

Operating Conditions

• Pressure: Up to 31.5 MPa (peak ratings up to 40 MPa for specialized variants).
• Temperature Range: –30°C to +100°C (limited to +40°C for flame-retardant fluids).
• Speed: Reciprocating speeds up to 0.5 m/s, depending on pressure and temperature.

Sizes & Variants

DAs seals are available in metric and inch dimensions, with examples including:

• 32 × 22 × 16.4 × 29.1 mm (bore × rod × groove × seal length).
• 80 × 60 × 35.1 mm (5-piece compact assembly).
• 125 × 100 × 38.1 mm (heavy-duty applications).

Customization Options:

• Type A: Shallow grooves with L-profile guide rings.
• Type B: Deeper grooves with Z-profile backup rings.
• DBM Variant: Concave backup rings for enhanced extrusion resistance.

Installation Best Practices

To maximize performance and longevity:

1. Groove Preparation: Remove burrs and sharp edges; chamfer groove entrances.
2. Lubrication: Apply a thin layer of hydraulic fluid to the seal and shaft.
3. Alignment: Press the seal squarely into the groove to avoid twisting.
4. Closed-Groove Installation: Use the seal’s stiff profile for snap-in placement without disassembling the cylinder.

Applications

DAs seals excel in environments requiring robust, space-efficient sealing:

• Mobile Equipment: Excavators, cranes, loaders.
• Agricultural Machinery: Tractors, harvesters, sprayers.
• Industrial Systems: Hydraulic presses, forklifts, machine tools.
• Material Handling: Lift tables, automated guided vehicles (AGVs).

Advantages

1. Space Efficiency: Combines five components into one, reducing groove complexity.
2. Extrusion Resistance: Backup rings provide bidirectional protection.
3. Wear Protection: POM guide rings enhance piston alignment and durability.
4. Simplified Inventory: Fewer parts to stock and manage.
5. Ease of Maintenance: Standardized sizes enable quick replacements.

Key Considerations

• Fluid Compatibility: Verify NBR compatibility with system fluids (e.g., HFD, HFA).
• Temperature Limits: Avoid exceeding material thresholds to prevent degradation.
• Gap Clearance: Ensure backup rings match system pressure and gap dimensions.

Conclusion

The DAs seal is a versatile, high-performance solution for hydraulic systems requiring compact, bidirectional sealing. By integrating sealing, guidance, and backup functions into a single unit, it simplifies design, reduces costs, and enhances reliability in medium- to heavy-duty applications. Engineers can optimize hydraulic cylinder performance by selecting the appropriate DAs seal variant based on pressure, temperature, and geometric requirements.