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Seals

HSC stocks hydraulic seals, O-rings, and cylinder rebuild kits for maintaining and repairing cylinders, pumps, valves, and fluid system components — urethane seals, wiper rings, Buna-N and Viton O-rings, back-up rings, and piston rings. Same-day availability, 40+ locations.

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Seals by Category

Image of Inch Sizes

Inch Sizes

Individual hydraulic seals in inch dimensions — including 70 and 90 durometer Buna-N O-rings, 90A urethane back-up rings, AN/BT/KW style urethane wiper rings, homogeneous Buna-N U-seals, cotton fabric and rubber piston cups, cast iron piston rings, and Caterpillar D-rings. The replacement seal inventory for hydraulic cylinder and component maintenance on equipment dimensioned to SAE inch standards.
Image of Metric Sizes

Metric Sizes

Hydraulic seals in metric dimensions — including metric urethane rod U-seals and Caterpillar D-rings — for maintaining and rebuilding hydraulic cylinders on European-manufactured equipment, imported machinery, and mobile equipment with metric-dimensioned cylinder bores and rod diameters.
Image of Assortment Kits & Tools

Assortment Kits & Tools

O-ring and seal assortment kits for comprehensive maintenance inventory — including Caterpillar D-ring kits, European and Japanese metric O-ring kits, flange O-ring seal kits, Teflon and urethane back-up ring kits, and Viton O-ring seal kits. Assortment kits provide the breadth of sizes needed to handle a wide range of seal replacements without sourcing individual seals for each job.
Image of Cynlinder Kits & Parts

Cynlinder Kits & Parts

Hercules complete hydraulic cylinder seal rebuild kits, bleeder valves, and telescopic cylinder parts — providing all the seals needed for a full cylinder rebuild in a matched kit format for specific cylinder applications, including dump truck telescopic cylinders. Eliminates the need to identify and source individual seals when a complete rebuild is the correct service approach.
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  1. Inch Sizes 896
  2. Metric Sizes 2
  3. Assortment Kits & Tools 14
  4. Cynlinder Kits & Parts 2
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How to Choose the Right Hydraulic Seal

Identify the seal type by function in the cylinder, match material to fluid and temperature, and measure dimensions carefully before ordering.

  • Identify the Seal Type by Function in the Cylinder Hydraulic cylinder seals serve distinct functions, and selecting the correct seal type for each position is the foundation of a successful rebuild. The rod seal (U-seal or lip seal) prevents fluid from escaping along the rod as it strokes. The wiper seal (scraper) removes contamination from the rod surface before it re-enters the cylinder — protecting the rod seal from abrasive particles. The piston seal (U-seal, O-ring with back-up ring, or piston cup) seals between the piston and cylinder bore to maintain pressure differential across the piston. The back-up ring prevents the O-ring from extruding into the clearance gap at high pressure. Each position requires the seal type designed for that dynamic or static loading condition — substituting seal types between positions creates premature failure.
  • Match Seal Material to the Hydraulic Fluid and Operating Temperature Seal material compatibility with the hydraulic fluid and operating temperature is non-negotiable. Buna-N (nitrile) is the standard material for petroleum-based hydraulic fluids at normal operating temperatures — compatible with mineral oil, and the most common hydraulic seal material. Urethane (polyurethane) provides higher abrasion resistance and better extrusion resistance than Buna-N for rod and wiper seal applications in high-cycle, high-pressure cylinders. Viton (fluoroelastomer) is specified for fire-resistant hydraulic fluids (phosphate ester, water glycol) and high-temperature applications where Buna-N degrades. PTFE back-up rings are chemically inert and compatible with virtually all hydraulic fluids. Confirm fluid compatibility before selecting a seal material — a Buna-N seal in a phosphate ester fire-resistant fluid circuit will swell, degrade, and fail rapidly.
  • Measure Carefully — Seal Dimensions Determine Fit and Performance Hydraulic seals are dimension-critical components. The seal must fit the groove it occupies with the correct cross-section, inside diameter, and outside diameter — too loose and the seal rolls and leaks; too tight and it distorts and tears during installation. For O-rings, identify the cross-section diameter and inside diameter. For U-seals and lip seals, identify the bore or rod diameter, the seal OD, and the seal height. When replacing a seal from a running cylinder, measure the groove dimensions as well as the existing seal — worn grooves may require a seal with different cross-section dimensions to seal correctly. If the original seal part number is available, use it; if not, bring the cylinder or the original seal to an HSC specialist for identification.

Featured In-Stock Seals

Best-sellers ready for immediate shipment.

  1. Polyurethane U-Seal, 1.38 Inch OD, 1.06 Inch ID, 0.25 Inch Height
    Polyurethane U-Seal, 1.38 Inch OD, 1.06 Inch ID, 0.25 Inch Height

    SKU: U12-1.12-25B

  2. Vee Packing Set, 2.00 Inch OD, 1.50 Inch ID, 1.00 Inch Height
    Vee Packing Set, 2.00 Inch OD, 1.50 Inch ID, 1.00 Inch Height

    SKU: VS15004X100

  3. Vee Packing Set, 2.50 Inch OD, 2.00 Inch ID, 0.88 Inch Height
    Vee Packing Set, 2.50 Inch OD, 2.00 Inch ID, 0.88 Inch Height

    SKU: VS20004X087

  4. Style QR Buna-N Quattro Rings, -212 Size, 5 Per Pack
    Style QR Buna-N Quattro Rings, -212 Size, 5 Per Pack

    SKU: QR-4212

  5. Vee Packing Set, 3.00 Inch OD, 2.50 Inch ID, 0.81 Inch Height
    Vee Packing Set, 3.00 Inch OD, 2.50 Inch ID, 0.81 Inch Height

    SKU: VS25004X082

  6. 70 Durometer Buna-N O-Ring, Inch OD, 1 Inch ID, 0.14 Inch Width
    70 Durometer Buna-N O-Ring, Inch OD, 1 Inch ID, 0.14 Inch Width

    SKU: A-214

  7. 70 Durometer Buna-N O-Ring, Inch OD, 2-3/4 Inch ID, 0.14 Inch Width
    70 Durometer Buna-N O-Ring, Inch OD, 2-3/4 Inch ID, 0.14 Inch Width

    SKU: A-232

  8. 90A Durometer Urethane Back-Up Rings -228 Dash Size, Per Pack
    90A Durometer Urethane Back-Up Rings -228 Dash Size, Per Pack

    SKU: 575-228

What Our Customers Say

Trusted by 50,000+ industrial clients.

“Always great service, always seem to have what you need. It’s our go-to when we’re on a job and need any hydraulic supplies.”

Jim Denman

Harvey, LA

“Awesome company. Great experience here every time with Rene. My husband and his associates in the pool construction business won’t use anyone else for their machinery. Highly reputable service provider.”

Amanda P.

Naples, FL

“Great staff, always helpful. Highly recommended.”

Gaige O’Neal

Harvey, LA

Technical Resources & Articles

Expert insights, maintenance tips, and industry news for hydraulic cylinder and component sealing.

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Industry Solutions

HSC works with industries that depend on reliable hydraulic and pneumatic systems, providing access to in-stock components, service capabilities, and knowledgeable support across diverse applications.

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Hydraulic excavator with boom and arm cylinders on an active earthmoving job site

Construction & Earthmoving

Heavy-duty hoses and cylinders built to withstand extreme conditions and vibration.

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Stainless steel hydraulic hose assemblies and marine-grade fittings on a shipyard vessel deck

Marine & Offshore

Corrosion-resistant stainless steel fittings and certified assemblies for marine environments.

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Factory floor with hydraulic press and pneumatic supply lines on a manufacturing production line

Manufacturing

Pneumatic automation and hydraulic power units to keep production lines moving.

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Agricultural tractor with hydraulic lift arm cylinders in a field

Agriculture

Durable fluid power systems designed to keep agricultural machinery operating at peak efficiency.

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Stainless steel food processing conveyor line with sanitary pneumatic fittings and valves

Food & Beverage

Expert fluid power solutions and components for food and beverage facilities.

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Airport tarmac ground support vehicle with hydraulic lines and fittings in foreground

Aircraft Ground Support

Precision hydraulic hose assemblies and fittings engineered for ground support vehicles and aircraft servicing equipment.

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Large aggregate crusher in operation at a quarry with visible hydraulic cylinders and hose lines

Aggregates & Cement

Heavy-duty hydraulic systems and hose assemblies built for the continuous demands of crushing, screening, and mixing operations.

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Hydraulic actuators and pneumatic cylinders on the mechanical undercarriage of an amusement ride

Entertainment & Theme Parks

Reliable hydraulic and pneumatic systems powering rides, stage equipment, and attractions safely and consistently.

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Automated packaging line with pneumatic cylinders and robotic arms on an industrial factory floor

Industrial & Packaging

Pneumatic cylinders and fluid power components engineered for high-cycle industrial automation and packaging lines.

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Municipal utility truck with extended hydraulic lift cylinder and hose lines

Government & Municipal

Certified hydraulic components and hose assemblies supporting the reliability demands of government fleets and municipal infrastructure.

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Paper mill interior with large rollers and hydraulic hose assemblies in a steam atmosphere

Paper & Pulp Mills

High-pressure hydraulic hoses and fittings built to withstand the high-moisture, corrosive conditions of paper and pulp production.

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Clean-room assembly line with precision pneumatic components and stainless steel fittings

Healthcare & Life Sciences

Precision hydraulic and pneumatic components meeting the cleanliness and reliability standards of medical and life science manufacturing.

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Mining drill rig with large hydraulic cylinders at an open-pit mine site

Mining & Extraction

Rugged hydraulic hoses, cylinders, and fittings built to perform in the demanding conditions of surface and underground mining.

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Telescoping crane truck with extended boom and prominent hydraulic cylinders on a job site

Mobile Machinery & Equipment

Complete hydraulic solutions keeping mobile equipment and specialty vehicles operating reliably across demanding field conditions.

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Oil field wellhead with hydraulic fittings and hose assemblies against a dramatic sky

Oil & Gas

High-pressure hydraulic hoses, fittings, and assemblies rated for upstream, midstream, and downstream oil and gas operations.

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Power plant interior with large turbine and visible hydraulic control lines and actuators

Power Generation

Hydraulic and pneumatic components built to the precision and reliability standards required by power generation facilities.

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Modern poultry processing facility with stainless steel conveyor equipment and pneumatic actuators

Poultry Processing

Sanitary-grade hydraulic and pneumatic components designed for the high-volume, wash-down conditions of poultry processing.

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Sterile pharmaceutical production line with stainless steel pneumatic valves and clean-room workers

Pharmaceutical

Clean-room-compatible fluid power components meeting the strict regulatory and contamination-control requirements of pharmaceutical manufacturing.

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Commercial semi-truck with hydraulic lift gate cylinder and hose lines at a logistics depot

Transportation & Logistics

Durable hydraulic hoses, cylinders, and fittings built to keep commercial vehicles and transport fleets operating at full capacity.

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Waste collection truck with hydraulic ram cylinder extended at a waste facility

Waste & Disposal

Heavy-duty hydraulic cylinders and hose assemblies built for the relentless demands of waste collection and compaction equipment.

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Industrial baler in a recycling facility with hydraulic ram and hose assembly visible

Recycling & Recovery

Robust hydraulic components and hose assemblies powering balers, shredders, and material handling equipment in recycling operations.

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Industrial Applications of Hydraulic Seals

Hydraulic seals are wear components that degrade predictably with every stroke and pressure cycle — and maintaining correct seal specifications is essential to cylinder performance. In construction equipment, failed cylinder seals cause fluid bypass past the piston and rod leakage. In industrial manufacturing, seal kit availability determines how quickly a cylinder is rebuilt and returned to service. HSC stocks seals, O-rings, and rebuild kits for major hydraulic cylinder, pump, and valve brands.

Hydraulic Seal Components Matter

A hydraulic seal is the barrier between high-pressure fluid inside the cylinder and the equipment and operator outside it. A seal that fails to hold rated pressure allows fluid bypass past the piston, rod leakage past the wiper, and uncontrolled actuator drift — consequences ranging from productivity loss to safety risk. HSC stocks urethane, Viton, and Buna-N seals, O-rings, and rebuild kits with same-day availability for major hydraulic cylinder and pump brands.

Frequently Asked Questions

How do I identify the correct replacement hydraulic seal for my cylinder?

The most reliable method is the OEM part number from the cylinder manufacturer’s service manual or parts catalog — Hercules and other seal manufacturers publish cross-references from OEM part numbers to their replacement seals. If the part number is unavailable, measure the cylinder bore diameter (or rod diameter for rod seals), the seal groove width and depth, and the existing seal cross-section and height. Bring these measurements and the original seal (if intact) to an HSC specialist — in most cases, the correct replacement can be identified from dimensions alone.

What is the difference between a U-seal and an O-ring with back-up ring for cylinder sealing?

A U-seal (lip seal) is a single-piece seal with a U-shaped cross-section that seals dynamically — the lips flex against the bore or rod surface and self-energize under system pressure, maintaining contact as the seal wears. An O-ring provides static or low-dynamic sealing; in dynamic cylinder applications at higher pressures, O-rings are used with Teflon or urethane back-up rings that prevent the O-ring from extruding into the rod-to-bore clearance gap under pressure. U-seals are generally preferred for the primary rod and piston sealing positions in hydraulic cylinders at moderate to high pressures; O-ring and back-up ring sets are common in lower-pressure dynamic applications and in many valve and fitting static seal positions.

What causes a hydraulic cylinder to develop an external rod seal leak?

The most common causes are: seal wear from high cycle count (normal service life); rod surface damage — scratches, chrome flaking, or corrosion pits that create leak paths through the seal contact zone; seal hardening from fluid incompatibility or heat exposure, which causes the lip to lose flexibility and contact force; and wiper seal failure that allows abrasive contamination to reach and damage the rod seal. If the rod surface is damaged, replacing the seal alone will not solve the leak — the rod must be repaired or replaced before the new seal will perform correctly.

When should I use Viton O-rings instead of Buna-N?

Viton (FKM) O-rings are required when the hydraulic fluid is a fire-resistant type — phosphate ester (Skydrol, Fyrquel), water glycol, or high-water-base fluid — where Buna-N is not compatible and will swell or degrade rapidly. Viton is also specified in high-temperature applications (above approximately 250°F continuous) where Buna-N’s heat resistance is exceeded. For petroleum-based hydraulic oils at normal operating temperatures, Buna-N is the standard and correct choice — Viton provides no performance advantage in petroleum fluid service and costs significantly more.

Does HSC stock hydraulic seals and cylinder kits for same-day pickup or shipping?

HSC maintains in-stock hydraulic seals — including Buna-N and Viton O-rings, urethane U-seals and wiper rings, back-up rings, piston cups, and cast iron piston rings — in both inch and metric dimensions, along with Hercules cylinder rebuild kits and O-ring assortment kits. Same-day shipping is available on orders placed before 2pm EST, and with 40+ branch locations throughout the Southeast, there is likely an HSC store near you with the seals you need already on the shelf.