Installation Method for Directional Control Valves of Small Dump Trucks

I. Pre-Installation Preparation

1. Safety and Tool Preparation

(1) Safety Protection

• Wear oil-resistant gloves, goggles, and non-slip work shoes to avoid injuries from hydraulic oil splashes, falling parts, or sharp edges.

• Before operation, shut down the engine, cut off the power supply, and release residual pressure in the hydraulic system (move the control valve handle to the neutral position and open the air release valve to relieve pressure).

• Park the dump truck on a level surface, secure the wheels with wheel chocks, lower the cargo box to the lowest position and lock it to prevent rolling or accidental lifting.

(2) Tool and Consumable Preparation

• Core Tools: Torque wrench (accuracy ±3%), hex key set (compatible with M6~M12 bolts), non-slip pipe wrench, copper scraper, high-pressure washer (or diesel/hydraulic oil cleaning agent), level, feeler gauge, multimeter (for testing solenoid coils).

• Consumables: Matching seals (O-rings, composite gaskets—preferably nitrile rubber, compatible with 46# anti-wear hydraulic oil), anti-loosening washers (spring washers + lock nuts), thread sealant (PTFE tape or anaerobic sealant), anti-rust lubricant, waterproof sleeves for solenoid coils (if required).

(3) System Preprocessing

• Clean the Hydraulic Oil Tank: Check the cleanliness of the oil. If impurities or moisture are present, completely replace with new oil and clean the tank filter and suction filter.

• Clean Pipes and Mounting Position: Purge the inner walls of hydraulic pipes with high-pressure air to remove iron filings, welding slag, and other impurities. If replacing an old valve, use a copper scraper to remove residual sealant and oil from the mounting surface, ensuring no burrs or depressions.

2. Component and Mounting Surface Inspection

(1) Directional Control Valve Inspection

• Model Compatibility: Verify that the valve’s pressure rating (16~21MPa for common small dump trucks), flow parameters (matching the hydraulic pump’s output flow, usually 30~60L/min), and interface size (thread specifications BSPP/NPT or mounting plate dimensions) are consistent with the original vehicle drawings. Ensure the nameplate parameters are clearly legible.

• Functional Testing: For manual directional valves, the handle should move smoothly without jamming, and the return spring should have good elasticity. For solenoid directional valves, use a multimeter to test the coil resistance (12V coils: approximately 2~5Ω; 24V coils: approximately 8~15Ω), ensuring the insulation layer is intact and the connector is in good condition.

• Visual Inspection: Check that the valve body has no cracks or blowholes, the interface threads are undamaged, the seal grooves are not deformed, and the mounting hole positions match the mounting plate.

(2) Mounting Surface and Pipe Inspection

• Mounting Surface Requirements: For plate-type valves, the flatness error of the mounting surface (valve block or frame mounting base) should be ≤0.02mm/m, with a surface roughness Ra=0.8~1.6μm. The surface must be dry, oil-free, and burr-free.

• Pipe Inspection: Hydraulic pipes should be free of aging, bulging, or cracks, and the pipe joint threads should be intact. Pipe routing must avoid high-temperature or moving parts such as the engine exhaust pipe and drive shaft, with a vibration compensation margin reserved.

• Positioning Datum: Confirm that the positioning pins (or holes) on the mounting base are intact to ensure precise alignment of oil passages after valve installation.

II. Core Installation Operations

1. Mounting Methods and Precise Alignment

(1) Plate-Type Installation (Mainstream Method, Suitable for Solenoid/Manual Directional Valves)

• Alignment: Slowly fit the valve body to the mounting surface, ensuring the positioning pins insert into the valve body’s positioning holes. Verify that the oil passage interfaces (P port - inlet, T port - return, A/B ports - connecting to the lift cylinder) are fully aligned with the mounting base’s oil passages—never force the valve body into place.

• Seal Installation: Place a new seal between the mounting surface and the valve body, ensuring the seal fully covers the oil ports without overlapping or distortion (to avoid high-pressure oil leakage).

• Fastening Sequence: Follow the principle of "diagonal uniform pre-tightening → torque final tightening." First, hand-tighten all bolts until the valve body fits the mounting surface, then use a torque wrench to final-tighten to the specified torque (M6 bolts: 8~10N・m; M8 bolts: 12~15N・m; M10 bolts: 25~30N・m). The bolt should extend 1~3 thread pitches beyond the nut.

• Anti-Vibration Reinforcement: Install double anti-loosening washers or apply thread lock adhesive to critical bolts to prevent loosening due to road bumps.

(2) Pipe-Type Installation (Suitable for Small Manual Valves)

• Thread Sealing: Wrap PTFE tape evenly around the pipe joint threads (3~5 wraps, winding direction consistent with thread rotation) or apply thread sealant, avoiding sealant entering the valve body.

• Valve Body Fixing: Use a pipe wrench to clamp the valve body’s hexagonal flat surface (never clamp the handle or coil) and tighten the pipe joint slowly. Adjust the torque based on pipe diameter (φ10~15mm pipes: 15~20N・m; φ18~25mm pipes: 25~35N・m).

• Pipe Routing: Reserve a flexible section of ≥80mm at the connection between the valve body and pipes, or install a corrugated pipe for protection. Secure pipes with clamps at intervals ≤400mm to avoid suspended vibration.

2. Key Requirements for Oil Passage and Interface Connection

• Oil Passage Marking Verification: Strictly follow the hydraulic schematic for connections: P port to the hydraulic pump’s outlet pipe, T port to the return pipe, and A/B ports to the rodless and rod chambers of the cargo box lift cylinder, respectively. Never reverse connections (otherwise, the cargo box lifting/lowering direction will be inverted, potentially damaging the cylinder).

• Drain Port Handling: If the valve is equipped with a drain port (L port), connect it to a separate return pipe leading directly to the oil tank. The pipe diameter should be no less than 6mm to avoid damage to the valve caused by connecting to high-pressure oil passages.

• Air Release Valve Installation: Install an air release valve on the pipe near the lift cylinder or at the highest position of the valve to facilitate air discharge from the system (air can cause sluggish or weak cargo box lifting).

3. Electrical Connection (For Solenoid Directional Valves)

• Wiring Verification: Confirm the coil voltage (12V or 24V for common small dump trucks) according to the original vehicle’s electrical schematic, ensuring compatibility with the power supply. The terminals should be clean and rust-free.

• Sealing Protection: After connecting the connector, wrap it with waterproof tape or heat-shrink tubing and install a waterproof sleeve to prevent rainwater and dust from entering, which could cause short circuits. Install the coil away from oil splash areas and high-temperature components.

• Wire Fixing: Secure wires to the frame with clamps, reserving a vibration margin to avoid friction with moving parts. Ensure connections are tight and free of loosening.

Special Precautions

1. Anti-Vibration Protection: Small dump trucks experience significant road bumps. All bolts must be equipped with anti-loosening measures. A small amount of anti-rust lubricant can be applied to the mounting surface to reduce vibration-induced wear.

2. Waterproof and Dustproof Protection: For vehicles operating outdoors, enhance the sealing of electrical interfaces, install waterproof sleeves for solenoid coils, and add dust covers to valve handles to avoid malfunctions caused by rainwater and dust.

3. Working Condition Adaptation: Avoid prolonged overload operation (e.g., lifting overloaded cargo boxes). Regularly inspect the condition of seals and coils, and shorten the maintenance cycle in harsh environments.

4. Genuine Part Compatibility: When replacing the control valve, prioritize original vehicle parts or reputable brand products of the same specification. Never arbitrarily replace valves with mismatched pressure or flow parameters to avoid system malfunction.

5. Troubleshooting: After installation, if issues such as sluggish cargo box lifting, jamming, or oil leakage occur, first check for reversed oil passages, seal failure, or unbled air. For solenoid valve malfunctions, inspect coil power supply and loose wiring.

Authoritative Information Sources

• Original maintenance manuals for small dump trucks (e.g., hydraulic system installation specifications for brands such as Foton, Dongfeng, JAC, etc.);

• Technical Conditions for Installation of Hydraulic Valves (JB/T 7940-2010);

• Technical manuals from hydraulic valve manufacturers (e.g., installation guides for small vehicle-specific valves from brands such as Huade, Eaton, Rexroth, etc.);

• General Technical Conditions for Automotive Hydraulic Systems (GB/T 14039-2002).