CAT 370-3211 CAP-UPPER

CAT 370-3211 is a cap-upper for Caterpillar hydraulic cylinders used in construction machinery. It is primarily designed for the top of the boom and stick cylinders of small and medium-sized excavators/loaders. Its core function is to seal the top of the cylinder, protect the internal piston rod and guide sleeve, and simultaneously position and secure the sealing components, ensuring stable operation of the hydraulic system under high-pressure conditions. The following is precise technical and application information:

Core Technical Parameters
Item Details
Part Model: CAT 370-3211 (3703211) Cylinder Cap, a high-pressure sealing end cap, with matching O-ring 1L-6388, dust ring 120-4562, and guide belt 374-6512 (same series sealing ring)

Core Material: QT500-7 ductile iron, galvanized and passivated surface, tensile strength 500 MPa, yield strength 320 MPa, hardness HB 170-230, single weight approximately 2.1 kg kg (4.63 lb)

Key Dimensions: Compatible cylinder inner diameter 120 mm, outer diameter 150 mm, height 35 mm, bolt hole diameter 14 mm (6 evenly distributed), sealing groove width 5 mm, depth 3 mm, compatible piston rod diameter 70 mm

Suitable Operating Conditions: Reciprocating motion seal for hydraulic system pressure ≤35 MPa (350 bar), compatible with mineral oil and synthetic hydraulic oil, operating temperature -20℃ to +100℃

Compatible Machines: CAT 305.5E2/306E2 excavators (boom cylinder), 906M loader (boom cylinder), 226D3 skid steer loader (hydraulic cylinder)

Core Compatibility: Compatible with the top of small and medium-sized hydraulic cylinders with a cylinder diameter of 120 mm, integrating sealing, dustproof, and guiding functions to ensure the accuracy of piston rod reciprocating motion.

Core Functions and Structural Features:
High-Pressure Seal: Integrated O-ring + dustproof ring + The guide belt with mounting grooves prevents hydraulic oil leakage and the entry of external dust and moisture into the cylinder, making it suitable for high-pressure reciprocating operation.

Structural Protection: The ductile iron material provides high rigidity, resisting impact and vibration, protecting internal precision components such as the piston rod and guide sleeve, and extending the cylinder’s service life.

Positioning and Guiding: Precisely positions the piston rod, controlling radial runout ≤0.1 mm, reducing abnormal wear on seals and the piston rod, and ensuring stable movement.

Installation and Maintenance Points
Installation Specifications: Clean the top cover, cylinder barrel ports, and seals, removing burrs, oil, and impurities. The groove surface roughness Ra ≤0.8 μm, free from impact damage.

Install the dust ring, O-ring, and guide belt/retaining ring in sequence, ensuring the seals are free from twisting and scratches. Tighten the top cover bolts in a diagonal sequence in 3 steps, with a torque of 85 N・m (62.7 lb-ft).

After installation, perform a pressure test (2 MPa, hold for 5 min). No leakage and smooth piston rod movement indicate successful installation.

Maintenance Recommendations:

Inspect the top cover seal every 1500 working hours. If oil leakage, dust seal damage, or guide belt wear exceeding 0.2 mm is found, replace the top cover seals simultaneously.

Control the hydraulic oil contamination level to NAS grade ≤ 8 to prevent impurities from causing abnormal wear on the seals and top cover.