Common Malfunctions Analysis and Improvement Suggestions for Manual (Leveraged) Hydraulic Forklifts

1. Malfunction: Cargo Descends Automatically or Too Slowly

Symptoms:

Cargo drops slowly or unexpectedly after lifting.

Door frame tilts asynchronously or fails to rise when unloaded.

Root Causes:

Hydraulic Valve Wear: The valve body or seat of the lift slide valve is damaged, causing oil leakage and insufficient pressure in the cylinder’s lower chamber.

Piston Seal Failure: High-pressure oil leaks from the piston seal into the upper chamber of the lift cylinder, reducing lifting force.

Tilt Valve Issues: Similar to lift valves, tilt valves may wear or have damaged seals, leading to pressure loss.

Diagnostic Steps:

Lift Cylinder Test:

Disconnect the return oil pipe at the top of the lift cylinder from the tank.

Operate the lift valve to raise the cargo.

If oil flows from the pipe: The piston seal is faulty.

If no oil flows: The lift slide valve is damaged.

Tilt Cylinder Test:

Disconnect the oil pipe at the rodless end of the tilt cylinder.

Tilt the door frame backward and observe for oil leakage.

If oil leaks: The tilt cylinder seal is faulty.

If no oil leaks but suction is felt: The tilt slide valve is damaged.

Improvement Suggestions:

Replace Worn Components:

For piston seals, install new seals and polish minor scratches on the cylinder wall with fine sandpaper.

For slide valves, repair or replace severely worn valve bodies/seats. Consider chrome plating or precision grinding for reconditioning.

Preventive Maintenance:

Regularly inspect and replace hydraulic oil filters (every 500 hours).

Clean hydraulic tanks and replace oil (every 1000 hours).

2. Malfunction: Weak Lifting Capacity

Symptoms:

Forklift fails to lift heavy loads or struggles during operation.

Root Causes:

Low Safety Valve Pressure: The spring in the multi-way directional valve’s safety valve weakens, reducing system pressure.

Gear Pump Failure: Wear in the pump housing or gear end faces decreases efficiency.

Air Ingress: Air entering the system causes cavitation, increasing oil temperature and reducing performance.

Diagnostic Steps:

Check Safety Valve:

Measure system pressure with a gauge. If pressure is below specifications, adjust or replace the safety valve spring.

Inspect Gear Pump:

Look for excessive clearance between the pump housing and gear teeth. Replace the pump if worn.

Check for Air Leaks:

Tighten loose hydraulic connections and top up oil levels to prevent air ingress.

Improvement Suggestions:

Adjust/Replace Safety Valve: Ensure pressure meets manufacturer specifications.

Replace Gear Pump: Use a new pump if efficiency drops significantly.

Bleed the System: Remove air by operating the lift cylinder with the return pipe disconnected.

3. Malfunction: Hydraulic Cylinder Crawling or Leakage

Symptoms:

Cylinder moves unevenly or leaks hydraulic fluid externally.

Root Causes:

Air Ingress: Air trapped in the cylinder causes erratic movement.

Seal Damage: Worn piston rod seals or gland seals lead to leakage.

Misalignment: Bent piston rods or misaligned cylinders cause uneven motion.

Diagnostic Steps:

Check for Air:

Operate the cylinder through its full stroke to expel trapped air.

Inspect Seals:

Look for cuts, swelling, or hardening in seals. Replace if damaged.

Measure Alignment:

Use a dial indicator to check piston rod straightness. Replace if bent.

Improvement Suggestions:

Replace Seals: Use OEM-specified seals for proper fit.

Realign Cylinder: Ensure proper installation to prevent binding.

Add Exhaust Valves: Install valves to facilitate air removal during maintenance.

4. Malfunction: Overheating and Noise

Symptoms:

Hydraulic oil temperature rises excessively, accompanied by unusual noises.

Root Causes:

Oil Contamination: Dirt or metal particles clog filters or damage components.

Incorrect Oil Viscosity: Using oil with unsuitable viscosity increases friction.

Pump Cavitation: Low oil levels or air leaks cause pump noise.

Diagnostic Steps:

Check Oil Level/Quality:

Ensure oil is at the correct level and free of contaminants.

Inspect Filters:

Replace clogged filters (every 250 hours for initial checks).

Listen for Cavitation:

A whining pump noise indicates air ingestion. Tighten connections and check oil levels.

Improvement Suggestions:

Use Proper Oil: Follow manufacturer recommendations for viscosity and type.

Clean System: Flush and replace oil if contaminated.

Tighten Connections: Prevent air leaks by securing all hydraulic fittings.

5. Malfunction: Brake Failure

Symptoms:

Forklift fails to stop or brake distance increases.

Root Causes:

Excessive Brake Shoe Clearance: Worn shoes or drum misalignment.

Master Cylinder Failure: Faulty valves or piston seals in the master cylinder.

Diagnostic Steps:

Check Clearance:

Adjust brake shoe clearance to manufacturer specifications.

Test Master Cylinder:

Inspect for leaks or stuck pistons. Replace if faulty.

Improvement Suggestions:

Replace Brake Shoes: Use high-quality linings for durability.

Service Master Cylinder: Rebuild or replace components as needed.

General Maintenance Tips

Regular Inspections:

Check for oil leaks, loose fittings, and worn components daily.

Lubrication:

Grease pivot points and bearings per manufacturer guidelines.

Operator Training:

Train operators to avoid rough handling, which accelerates wear.

Record-Keeping:

Maintain logs of repairs and maintenance to track component life.

By addressing these common malfunctions proactively, operators can enhance safety, reduce downtime, and extend the lifespan of manual hydraulic forklifts.

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