X Ring Seal Ideal for Hydraulic Mechanical & Industrial Equipment Sourcing

In sealing systems, X-rings, often called star-shaped seals, are instantly
recognizable for their four-lip cross-section: their cross-section resembles a
distinct "X." They can be installed in specialized, low-compression grooves to
reduce friction, or they can directly utilize the AS568A standard O-ring groove
and dimensions, effectively replacing O-rings in most applications without
significantly modifying the hardware structure.

Definition and Mechanism

·Structural Features: They have an X-shaped cross-section and four lips acting
on the sealing surfaces. After pre-compression, they establish contact stress
in the radial and axial directions. Higher system pressures increase the
sealing force, making them a "pressure-energized" seal.

·Operating Condition Compatibility: They can be used for both static sealing
and reciprocating and rotating applications. The four lips provide greater
stability in dynamic conditions, resist rolling or twisting, reduce starting
resistance, and facilitate lubrication development and retention.

· Materials and Temperature: Common materials include nitrile rubber (NBR) and
fluororubber (FKM), with a typical operating temperature range of -40°C to
+250°C. Applicable media include hydraulic oil, water, and gas.

· Interchangeability and Grooves: Standard dimensions align with American
Standard AS568A O-rings, allowing direct use of O-ring grooves of the same
specification. To further reduce friction and wear, a dedicated X-shaped seal
groove with a lower compression ratio can also be used.

Differences and Advantages Compared to O-rings

· Lower Friction and Starting Resistance: The "lubrication cavity" between the
sealing lips facilitates oil film formation, resulting in easier starting and
slower wear.

· Torsion Resistance and Stability: The non-circular cross-section suppresses
rolling and torsion during reciprocating motion, reducing premature leakage
caused by instability.

· Optimized Sealing Details: The flash edge is located in the concave portion
of the cross-section, which more easily focuses contact pressure on the
effective sealing area, improving sealing reliability.

Number of contact lines: Four contact lines, compared to two for an O-ring,
provide more ample sealing contact and compressive stress distribution.

High-pressure capability: With appropriate groove, tolerance, and support
configurations, high-pressure operating conditions can reach 60 MPa. For
extreme pressures or large gaps, it is recommended to consider the stiffness of
both the retaining ring and the mating component.

Groove and Selection Key Points

Universal Installation: The O-ring groove can be directly used. For lower
friction and longer life, a dedicated X-shaped seal groove is recommended
(which offers a milder compression rate, lower dynamic friction, and heat
generation).

Dimensional Recommendations: For static seals (for holes): The matching
difference between the seal ring inner diameter and the groove outer diameter
should be controlled within approximately 2% to achieve appropriate
interference fit and preload. For rotary seals (for shafts): The seal ring
inner diameter is typically approximately 2–5% larger than the shaft diameter
to account for thermal expansion, frictional heat generation, and lubricant
film stability.

· Dynamically Prefer Thicker Sections: For dynamic applications such as
reciprocating and rotating, thicker sections are preferred for more
controllable compression set, greater wear resistance, and greater sealing
margin. Smaller sections are also suitable for static sealing.

· Operating Condition Review: The selection process should comprehensively
consider temperature (peak and continuous), pressure (including pulsation),
media, motion type, and cycle. For rotating applications, the temperature rise
and heat dissipation capacity caused by frictional heat should also be
evaluated.

Material and Operating Condition Matching

· Nitrile (NBR): Compatible with most mineral-based hydraulic fluids and
greases, it offers a balance of low-temperature performance and wear
resistance, making it a "basic" for hydraulics and general machinery.

· Fluorocarbon (FKM): Demonstrates stronger adaptability to higher
temperatures and a variety of chemical media, making it suitable for oil and
gas, chemical, powertrain, and some energy equipment.

· Hardness and Formulation: Commonly found in the 70–90 Shore A range; higher
hardness improves pressure resistance and extrusion resistance, but a balance
must be struck between assembly requirements and low-temperature flexibility.

· Pressure and Clearance: For high-pressure or large radial clearance
applications, retaining rings/stops are recommended. The roughness and hardness
of the sealing surface also directly affect the lifespan and leakage level.

Application Scenarios and Audience

· Pumps and Hydraulic Systems: For both reciprocating and rotary sealing,
star-shaped seals offer reliable performance in shaft seals and plunger/piston
rod applications.

· Motors, Gearboxes, and Engines: They balance lubricant retention and torsion
resistance, making them suitable for auxiliary oil seals at shaft ends and end
caps.

· Industrial Machinery and Robotics: Comprehensive sealing solutions for
reciprocating actuators, rotary joints, and reducer interfaces.

· Construction Machinery and Energy Equipment: Ensures seal reliability and
lifespan management under high loads and pulsating pressures.

· Wind Power, Metallurgy, Chemical Engineering, Water Treatment, and
Shipbuilding/Rail Transit/Automobile (including heavy-duty trucks): These seals
cover a wide range of applications, from static sealing flanges to dynamic
bearings.

If your system needs to reduce friction and starting resistance, inhibit
torsion and extrusion, and maintain high compatibility with existing AS568A
structures, a star seal (X-ring) is a good choice. Provide key operating
conditions (temperature/pressure/media/motion type/clearance), and DEDE can
quickly provide recommendations for selecting and sampling the X-ring series.

Minimum Order: 1000 pieces

Click to Enlarge