Excavator Arm Hydraulic Cylinder
Toleng manufactures high-performance excavator arm hydraulic cylinders (also known as stick cylinders or crowd cylinders) designed for demanding digging and loading applications. Our arm cylinders are engineered with precision control, durable sealing systems, and high-strength materials to deliver reliable performance through millions of cycles.
What Is an Excavator Arm Hydraulic Cylinder?
An excavator arm hydraulic cylinder (also called a stick cylinder, dipper cylinder, or crowd cylinder) is a double-acting hydraulic cylinder that controls the movement of the excavator's dipper arm (stick). It extends the arm forward for reach and retracts it inward for digging and loading operations.
The arm cylinder is the most actively cycled of the three working attachment cylinders (boom, arm, and bucket), making it statistically the most frequently rebuilt cylinder on a working excavator over its service life.
How Does an Excavator Arm Cylinder Work?
The arm cylinder operates using pressurized hydraulic oil supplied by the excavator's main pump.
Crowd Inward (Digging)
High-pressure flow from the main pump is directed to the cap end of the arm cylinder, extending the rod and pulling the dipper arm inward through the digging arc.
Extend Outward (Reach)
Pressure is applied to the rod end, retracting the cylinder and extending the arm forward to its maximum reach position, ready for the next digging pass.
Dynamic Load Profile
Unlike the boom cylinder which primarily sustains static holding load, the arm cylinder works dynamically through its full stroke on virtually every digging cycle.
Pressure Range
Arm cylinders operate at similar pressure ratings to boom cylinders, typically between 250 and 350 bar (25-35 MPa) on modern excavators.
Continuous Cycling
This continuous dynamic cycling places significant fatigue demands on rod seals, wiper rings, and piston seals, making arm cylinders the most frequently serviced cylinders on an excavator.
Precise Control
Equipped with advanced sealing and buffering systems, arm cylinders provide smooth, controlled movement for precise digging and loading operations.
Main Components
Understanding the key parts of an excavator arm hydraulic cylinder.
| Component | Function |
|---|---|
| Cylinder Barrel | Houses the piston assembly, precision-honed for smooth operation |
| Piston Rod | Transfers force to the dipper arm, chrome-plated for wear resistance |
| Piston | Separates cap and rod chambers, with seals to prevent bypass |
| Rod Gland | Supports and seals the rod, houses the rod seal and wiper |
| Rod Seal | Prevents hydraulic oil leakage from the rod end |
| Wiper Ring | Removes dirt and debris from the rod surface during retraction |
| Wear Ring | Reduces metal-to-metal contact between piston and barrel |
| Buffer System | Absorbs impact at stroke end, reducing shock and noise |
| Clevis/Pin Mount | Connects cylinder to the boom and dipper arm |
| Hydraulic Ports | Oil inlet and outlet for cap and rod chambers |
Key Features
Engineered for durability, precision, and long service life.
Heavy-Duty Alloy Steel
Made from 42CrMo high-strength alloy steel with pressure resistance up to 35 MPa.
Hard Chrome Plated Rod
Induction-hardened (HRC 50-55) and hard chrome plated rod surface for superior wear resistance.
Dynamic Seal System
Triple-sealing system with main seal, dust shield, and dust scraper ring to prevent contamination.
Precise Control
Equipped with buffer valve for smooth movement, enhancing control by up to 40%.
Fast Response
Low starting force (≤ 0.5 MPa) and reduced cycle time for improved productivity.
Extended Service Life
Optional laser fusion coating (HRC 60+) on piston rod for extreme durability.
Typical Technical Specifications
Custom dimensions vary by excavator model and application requirements.
| Parameter | Typical Range |
|---|---|
| Bore Diameter | 50 – 200+ mm |
| Rod Diameter | 30 – 160 mm |
| Stroke Length | 600 – 3000+ mm |
| Working Pressure | 25 – 35 MPa (250 – 350 bar) |
| Test Pressure | Up to 52.5 MPa |
| Maximum Pressure | Up to 50 MPa (7,250 PSI) |
| Temperature Range | -40°C to 120°C |
| Mounting Style | Pin-eye / Clevis |
| Cylinder Type | Double-Acting Welded Cylinder |
Excavator Applications
Arm cylinders are used across all excavator sizes and types.
Mini Excavators
Compact arm cylinders for small excavators (1-6 tons)
Medium Excavators
Standard-duty arm cylinders for general construction (7-30 tons)
Heavy Excavators
High-load arm cylinders for large-scale projects (30-80 tons)
Mining Excavators
Extreme-duty arm cylinders for mining applications (80+ tons)
Common Arm Cylinder Failures & Symptoms
Arm cylinder degradation follows a recognisable progression from early seal wear through to structural failure.
Arm Drifting Inward Under Load
- The dipper arm slowly crowds inward when not commanded
- Indicates internal bypass past worn piston seals
Reduced Crowd Force During Digging
- Less pushing force during the crowd stroke
- Results in shallower bucket penetration
Slow Arm Movement at Full Throttle
- Reduced cylinder flow from internal bypass
- Seal degradation slows arm stroke speed
Visible Rod Seal Oil Leakage
- Oil streaking from the rod seal end
- Most visible and common early symptom
Scored, Pitted, or Corroded Cylinder Rod
- Physical rod surface damage destroys replacement seals rapidly
- Will consume seal kits repeatedly without resolving the leak
Preventive Maintenance Tips
- Inspect rod surface daily for scratches and pitting
- Clean exposed rod before retracting to prevent dirt ingress
- Replace seals at recommended intervals (every 2,000–4,000 hours)
- Change hydraulic oil per equipment manual
- Monitor system pressure regularly
- Lubricate mounting pins to prevent side loading
- Inspect welds and mounting points for cracks
OEM Arm Cylinder Manufacturing Process
Every arm cylinder is produced through a rigorous quality-controlled process.
How to Choose the Right Arm Cylinder
Consider these specifications when selecting a replacement or custom arm cylinder.
| Selection Factor | Recommendation |
|---|---|
| Bore Size | Match OEM design or application load requirements |
| Stroke Length | Match dipper arm geometry and required reach |
| Working Pressure | Match excavator hydraulic system pressure (typically 25-35 MPa) |
| Rod Diameter | Ensure sufficient buckling resistance for digging forces |
| Mounting Style | Match original pin dimensions (clevis/pin-eye) |
| Seal Material | Suitable for operating temperature and environment |
| Surface Finish | Hard chrome or laser fusion coating for wear resistance |
| Quality Standard | ISO 9001 certified manufacturing with 100% testing |
Arm Cylinder Specifications by Brand
Reference specifications for major excavator brands.
| Brand / Model | Bore × Stroke × Rod |
|---|---|
| Komatsu PC70-8 | 100mm × 865mm |
| Komatsu PC200-8 | 135mm × 1490mm × 95mm |
| Komatsu PC220-7 | 135mm × 1490mm × 95mm |
| Komatsu PC240LC-8 | 140mm × 1635mm × 100mm |
| Komatsu PC360-7 | 160mm × 1825mm × 110mm |
| Komatsu PC800-8R | 200mm × 2250mm |
| Caterpillar 312GC | 105mm × 1194mm |
| Caterpillar 320D2GC | 140mm × 1504mm |
| Caterpillar 324D | 140mm × 1660mm |
| Caterpillar 340DL | 170mm × 1738mm |
| Caterpillar 374DL | 210mm × 2118mm |
| Doosan DX225LC | 140mm/100mm × 1450mm |
| Doosan DX300LC | 150mm/110mm × 1580mm |
Frequently Asked Questions
Quick answers about excavator arm hydraulic cylinders.
What does an arm cylinder do on an excavator?
The arm cylinder controls the movement of the excavator's dipper arm (stick), allowing it to extend outward for reach and crowd inward for digging and loading operations.
How long does an excavator arm cylinder last?
The arm cylinder is the most frequently cycled of the three attachment cylinders. With proper maintenance and quality seals, it can last 5,000–10,000 hours, but seal kits may need replacement every 2,000–4,000 hours depending on operating conditions.
What causes an excavator arm to drift inward?
Arm drifting inward under load typically indicates internal bypass past worn piston seals, causing the arm to creep inward under the weight of the attachment.
Can an arm cylinder be repaired or does it need replacement?
Many arm cylinder issues can be resolved by replacing the seal kit and servicing the cylinder. However, if the rod is scored, pitted, or bent, or if the barrel is damaged, replacement may be required.
What is the working pressure of excavator arm cylinders?
Arm cylinders typically operate at 250 to 350 bar (25 to 35 MPa), similar to boom cylinders, but under a fundamentally different load profile with continuous dynamic cycling.
What is the difference between boom, arm, and bucket cylinders?
Boom cylinders lift the entire boom assembly, arm cylinders control the dipper arm reach and crowd, and bucket cylinders control bucket digging and dumping. The arm cylinder is the most actively cycled of the three.
Do you manufacture arm cylinders for Caterpillar / Komatsu / Volvo?
Yes, Toleng manufactures replacement and OEM arm cylinders for all major excavator brands, including Caterpillar, Komatsu, Volvo, Doosan, Hitachi, Hyundai, Kobelco, and Sany.
What seals are used in excavator arm cylinders?
Arm cylinders typically use a triple-sealing system including a main seal, dust shield, and dust scraper ring to prevent contamination and ensure reliable operation.
Need a Custom Excavator Arm Cylinder?
Send your excavator model or cylinder drawings. Toleng provides OEM boom cylinder solutions for construction equipment manufacturers worldwide.