1. Product Overview
Sany 75 Main Relief Valveis a critical safety component in the hydraulic system of Sany Heavy Industry’s 75-ton excavators (e.g., SY75C, SY75N models). Its primary functions include:
• Limiting system maximum pressureto prevent damage to hydraulic pumps, hoses, or actuators (e.g., cylinders) from overpressure.
• Ensuring operator safetyby avoiding equipment failures or accidents caused by pressure surges.
• Maintaining system stabilityby balancing pressure during sudden load changes.
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2. Technical Specifications (Typical Values)
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Parameter Description
Model SANY-RV-75 (Example; refer to Sany’s official part number)
Applicable Models SY75C, SY75N, SY75H, and other 75-ton excavators
Rated Pressure 35 MPa (350 bar; some variants up to 40 MPa)
Adjustment Range 20–35 MPa (manual or remote adjustable)
Flow Capacity 120–150 L/min (matched to pump displacement)
Response Time ≤10 ms (rapid opening under pressure surges)
Port Type Threaded (e.g., M20×1.5) or flange-mounted (design-dependent)
Seal Material Nitrile Butadiene Rubber (NBR) or Fluorocarbon Rubber (FKM, for high-temp/oil resistance)
Weight Approx. 2.5–3.5 kg
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3. Structure & Operating Principle
Key Components
1. Valve Body: High-strength alloy steel (e.g., 42CrMo) for pressure resistance.
2. Main Spool: Precision-ground conical or slide valve for oil flow control.
3. Pressure Spring: Replaceable spring set for pressure setting.
4. Pilot Valve: Integrated proportional减压阀 (pressure-reducing valve) in some models for remote adjustment.
5. Seals: Composite seal rings to prevent high-pressure leakage.
Working Logic
• Normal Operation: Spool remains closed, directing hydraulic fluid to actuators (e.g., boom cylinders).
• Overpressure Condition: When system pressure exceeds the set value, the spool opens against spring force, diverting fluid to the tank to stabilize pressure.
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4. Common Failures & Diagnostics
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Symptom Potential Causes Solutions
Pressure Fails to Build Broken spring, stuck spool, pilot valve failure Replace spring, clean spool, inspect pilot circuit
Pressure Fluctuations Aged seals, contaminated oil, fatigued spring Replace seals, filter oil, adjust/replace spring
Excessive Valve Noise Worn valve port, abnormal oil viscosity, system resonance Repair port, replace hydraulic fluid, adjust mounting position
Frequent Relief (Overheating) Overloaded system, degraded pump efficiency, low pressure setting Check load matching, repair pump, readjust pressure setting
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5. Selection & Replacement Guide
Critical Matching Parameters
1. Pressure Rating: Must be ≥ system maximum working pressure (with 10%–20% margin).
2. Flow Requirement: Select based on pump displacement (e.g., for 100 L/min pump, choose ≥120 L/min valve).
3. Mounting Dimensions: Verify thread size, length, and bolt patterns against original valve.
4. Control Method:
• Manual Adjustment: Suitable for fixed operations.
• Electronic Proportional: Requires controller integration for dynamic pressure adjustment (e.g., SY75N smart models).
Alternative Models
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Brand/Model Application Scenarios
Sany Original RV-75 Best compatibility; recommended first choice
Rexroth DBW10 High-performance alternative; requires interface adaptation
Yuken DSHG-10 Cost-effective option for non-smart models
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6. Maintenance Recommendations
1. Regular Inspection: Check seals, spring condition, and port wear every 500 hours.
2. Fluid Cleanliness: Maintain NAS Class 6 or better to prevent spool sticking.
3. Pressure Calibration: Annual calibration using a pressure tester (accuracy ≤±2%).
4. Storage: Store in a dry environment with rust-preventive oil on ports; avoid prolonged high-pressure preloading.
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7. Industry Applications
Beyond excavators, this valve type is used in:
• Cranes: Outrigger hydraulic system overpressure protection.
• Road Rollers: Vibratory drum hydraulic circuit safety control.
• Industrial Equipment: Hydraulic presses, injection molding machines requiring high-pressure control.
