Types of O-Ring Kits We Supply
Imara Engineering supplies o-ring kits in two primary formats to cover every maintenance and repair application on your excavator:
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Comprehensive Assortment Kits — Large-format o-ring assortment kits covering a wide range of sizes in a single supply, organised by diameter and cross-section in a compartmentalised storage case. Ideal for workshop maintenance operations, fleet service teams, and site repair kits where a broad size range is needed immediately without waiting on individual part sourcing. These kits cover the full size range encountered across all major excavator hydraulic circuits from pilot connections through to main pump port seals.
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Application-Specific O-Ring Sets — Targeted o-ring sets containing the exact o-ring sizes and quantities required for a specific component rebuild or circuit service pump overhaul sets, valve block port sets, cylinder gland sets, and hose fitting sets. Application-specific sets eliminate the guesswork of selecting the correct sizes from a large assortment and ensure every o-ring in the set is the correct dimension and elastomer grade for the specific assembly being serviced.
O-Ring Elastomer Materials: Choosing the Correct Grade
O-ring material selection is as critical as dimensional accuracy the wrong elastomer grade in a hydraulic application causes rapid seal degradation regardless of dimensional fit. These are the primary o-ring elastomer grades used across excavator hydraulic systems:
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Nitrile Rubber (NBR) — The standard elastomer for the vast majority of excavator hydraulic o-ring applications. Compatible with mineral-based hydraulic oil, engine oil, and gear lubricants across the normal operating temperature range of most excavator hydraulic circuits. NBR o-rings are the correct grade for most pump, motor, cylinder, valve, and hose fitting applications on machines running standard mineral hydraulic oil.
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Fluorocarbon Rubber (FKM / Viton) — High-temperature and chemically resistant elastomer for applications involving elevated operating temperatures, fire-resistant hydraulic fluids, or synthetic lubricants. FKM o-rings are required on machines running fire-resistant or synthetic hydraulic fluids, and are often specified for high-temperature circuit locations such as pump case drain ports and hydraulic oil cooler connections on heavy-duty applications.
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Polyurethane (PU) — High-abrasion resistance elastomer used in dynamic sealing applications within hydraulic cylinders — rod seals, piston seals, and wiper seals where reciprocating motion and surface contact demand higher wear resistance than standard NBR provides. Not typically used for static face seal applications.
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EPDM — Ethylene propylene elastomer compatible with water-based and phosphate ester hydraulic fluids. Not compatible with mineral oil — EPDM o-rings must never be used in standard mineral oil hydraulic circuits as they swell and disintegrate rapidly on contact.
When ordering o-ring kits, always confirm your machine's hydraulic fluid type with our parts team to ensure the correct elastomer grade is supplied for your specific application.
O-Ring Standards and Thread Specifications on Excavators
Excavators from different brands and production eras use different o-ring standards and port thread specifications, meaning o-ring dimensions are not universally interchangeable across all machines. Understanding which standard your machine uses is essential for correct o-ring selection:
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Metric O-Rings — Used as the primary o-ring standard across Japanese brands, including Komatsu, Hitachi, and Kobelco. Sized by inner diameter and cross-section in millimetres — the most common standard encountered on excavators working across African and Asian markets.
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Imperial O-Rings (AS568) — The American standard o-ring sizing system used predominantly on Caterpillar and Case machines, sized by dash number corresponding to specific inner diameter and cross-section dimensions in inches. Dimensionally distinct from metric o-rings, even where sizes appear similar, always confirm the standard before ordering.
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BSP Face Seal O-Rings — Used at British Standard Pipe threaded port connections throughout hydraulic circuits on many European and Asian machines. These o-rings seat in a machined groove on the port face rather than in the thread, providing a positive face seal rather than a thread seal.
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ORFS O-Rings (O-Ring Face Seal) — Used at ORFS hose end fittings and adaptor connections throughout circuits on many modern excavators. These o-rings provide a positive flat-face seal at hose and tube end connections and are available in both metric and imperial sizing depending on the fitting standard.
Our parts specialists will confirm the correct o-ring standard and sizing system for your specific machine before your order is placed.
Where O-Rings Are Used on an Excavator
O-rings serve as the primary static and semi-dynamic sealing element at virtually every hydraulic connection point on a working excavator. Key application locations include:
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Hydraulic pump and motor housing faces — O-rings at every housing split face, end cover joint, and port connection on pump and motor assemblies, maintaining internal pressure containment at all housing interfaces.
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Hydraulic cylinder gland and end cap — O-rings in the rod gland assembly and cap end of every boom, arm, and bucket cylinder, supporting and backing the primary rod and piston seals.
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Main control valve block ports — O-rings at every function port, pilot port, tank port, and pump port on the main control valve body, preventing external leakage at all circuit connections to the valve block.
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Hose end fittings and adaptors — O-rings at every hydraulic hose end fitting connection throughout the machine — are the most frequently disturbed o-ring locations during routine hydraulic maintenance and hose replacement.
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Relief valves and regulator valves — O-rings at valve body threads and port connections throughout the relief and regulator valve circuit, maintaining fluid containment at all valve installation points.
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Center joint port connections — O-rings at all upper structure and undercarriage port connections to the center joint body, maintaining circuit integrity at the rotary union connection points.
O-Ring Kit Models and Coverage
Imara Engineering supplies hydraulic o-ring kits covering all major excavator brands and model series. Our kits are available in a comprehensive assortment format and application-specific configurations for:
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Komatsu — PC200-7, PC200-8, PC210-8, PC300-7, PC300-8, PC360-7, PC400-7, PC400-8, PC450-8
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Caterpillar (CAT) — 320C, 320D, 320D2, 323, 325C, 325D, 330C, 330D, 336D, 336E
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Hitachi — ZX200-3, ZX210-3, ZX300-3, ZX330-3, ZX450-3, ZX500-3, EX200-5, EX300-5
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Volvo — EC210B, EC240B, EC290B, EC380, EC480, EC700
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Doosan — DX225LC, DX300LC, DX380LC, DX480LC
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Kobelco — SK200-8, SK300, SK350-8, SK480, SK850
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Hyundai — R210LC-9, R290LC-9, R380LC, R480LC
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Case — CX210, CX300, CX350, CX470
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Bobcat — E35, E50, E85 compact excavator range
Cannot find your machine model listed? Contact our parts team with your machine serial number and application details, and we will confirm the correct o-ring kit format, elastomer grade, and size range for your specific requirements immediately.
Related Hydraulic Parts You May Need
O-ring kits are most commonly required alongside wider hydraulic component servicing. Consider sourcing these components together with your o-ring kit:
- Pump Seal Kits — Complete pump seal kits including all o-rings, shaft seals, and internal sealing components for full pump overhaul
- Motor Seal Kits — Complete motor seal kits for travel and swing motor rebuilds, including all o-rings and dynamic sealing components
- Hydraulic Cylinder Seal Kits — Full cylinder seal kits including rod seals, piston seals, wiper rings, and all o-rings for complete cylinder rebuilds
- Center Joint Seal Kits — Complete swivel joint seal kits, including all circuit seal rings and o-rings for full center joint overhaul
- Hydraulic Hoses & Pipes — Replace hose end fitting o-rings alongside any hose replacement for a complete leak-free circuit repair
