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General safety rules and precautions for maintenance and repair.
Explanation of warning and caution symbols used in the manual.
Description of the electro-hydraulic main control valve and variable displacement pump.
Overview of the different sections of the electronic main control valve assembly.
Procedures for removing the main control valve from the truck.
Procedures for removing and disassembling the outlet control valve section.
Procedures for disassembling and cleaning the auxiliary control valve section.
Disassembly and cleaning procedures for the tilt control valve section.
Disassembly and cleaning procedures for the lift/lower control valve section.
Procedures for removing, cleaning, and inspecting the transition section.
General safety rules and precautions for maintenance and repair.
Explanation of warning and caution symbols used in the manual.
Description of the electro-hydraulic main control valve and variable displacement pump.
Overview of the different sections of the electronic main control valve assembly.
Procedures for removing the main control valve from the truck.
Procedures for removing and disassembling the outlet control valve section.
Procedures for disassembling and cleaning the auxiliary control valve section.
Disassembly and cleaning procedures for the tilt control valve section.
Disassembly and cleaning procedures for the lift/lower control valve section.
Procedures for removing, cleaning, and inspecting the transition section.
This document outlines the service and repair procedures for the main control valve with a variable displacement pump, specifically for Hyster U005 (H80FT, H90FT, H100FT, H110FT, H120FT) and S4.0FT, 4.5FT, 5.5FT, S5.5FTS (S80, 100, 120FT; S80, 100FTBCS; S120FTS; S120FTPRS) forklift models. The main control valve is an electro-hydraulic (E-Valve) unit, electronically controlled and mounted to the cowl using three mounting bolts. It operates with a closed-center, single-function compensated system, utilizing parallel hydraulic circuitry. Load sensing is performed through the variable displacement pump (VDP).
The E-Valve with VDP is designed to manage multiple hydraulic functions simultaneously. When multiple functions are operated, the system ensures a non-proportionate increase in pump flow to functions that receive the lowest amount of pressurized fluid. This hydraulic circuitry incorporates dual pressure relief logic to maintain system integrity and performance.
A key feature of this system is the regulation of lift function pressure by the pump pressure compensator. The pump compensator is set to the maximum system pressure, and a clipper relief valve, located in the transition section of the valve, is set slightly higher. This clipper relief valve adjustment is tamper-proof, meaning it should not be disassembled or adjusted, as doing so will void any warranties. This design ensures that lift pressure remains unaffected by secondary relief operation, which applies to tilt and auxiliary functions.
The electronic main control valve with variable displacement pump assembly is modular, divided into several sections: the Steering Control Unit (SCU), Transition section, Lift/Lower section, Tilt section, Auxiliary section(s), and Outlet section. This modular design facilitates targeted repairs and maintenance.
For usage, the system ensures precise control over various forklift operations. The electronic control allows for smoother and more responsive handling compared to purely mechanical systems. The load-sensing capability optimizes hydraulic power usage, contributing to fuel efficiency and reduced wear on components. The dual pressure relief logic enhances safety by preventing over-pressurization in different hydraulic circuits.
Maintenance and repair procedures are detailed to ensure the longevity and safe operation of the forklift. Before any maintenance or repair, it is crucial to lower the carriage completely, position the mast vertically, and disconnect the battery connector (for electric trucks) or the battery ground cable (for internal combustion trucks). Proper blocking of the unit is essential to prevent rolling or falling.
Cleaning is a critical step in maintenance. Before disconnecting any hydraulic hoses or removing parts, the exterior of the control valve must be thoroughly cleaned using steam or cleaning solvent. All openings must be immediately plugged or covered to prevent contamination from entering the hydraulic system. Cleaning solvents can be flammable and toxic, requiring adherence to manufacturer's safety procedures, including wearing protective goggles or a face shield. Similarly, compressed air, used for drying, must be handled with caution to prevent eye injuries.
When disassembling the main control valve, it is important to note that most individual valve components can be removed and replaced while the control valve remains installed in the truck. Complete removal of the control valve is typically only necessary for replacing an entire valve section or the O-rings between sections. The main control valve is heavy, weighing approximately 30.5 kg (67 lb), necessitating the use of a lifting device to prevent injury.
During disassembly, all connectors should be tagged prior to disconnection to aid in correct reassembly. Special attention is required when working on individual sections, such as placing a cover over remaining sections to prevent contamination. If O-rings are being replaced due to a hydraulic oil leak between two sections, all O-rings between all sections should be replaced to prevent future leaks.
The document provides specific instructions for disassembling, cleaning, inspecting, and assembling each section: Outlet Control Valve, Auxiliary Control Valve, Tilt Control Valve, and Lift/Lower Control Valve. For instance, the Outlet Control Valve section involves removing nuts from tie rods and discarding O-rings. The secondary relief valve, if leaking, is also addressed here, with instructions for removing its components. Inspection involves checking mating surfaces and bores for damage; any damaged components, other than O-rings and backup rings, should be replaced. If a section is not immediately reassembled, its surfaces should be coated with clean hydraulic oil and covered to prevent rust and contamination.
The Auxiliary Control Valve section may have one or two parts depending on the number of functions on the forklift. The repair procedures for both auxiliary sections are identical. The Tilt Control Valve section and Lift/Lower Control Valve section also have detailed removal, disassembly, cleaning, inspection, and assembly steps, emphasizing the replacement of O-rings and proper torque specifications for plugs and capscrews.
The Transition section is unique due to its tamper-proof clipper relief valve. Disassembly or adjustment of this valve is strictly prohibited and will void warranties. The emergency load lowering valve, located in this section, requires careful handling during removal to avoid damaging its tip.
Installation involves reversing the removal steps, with careful attention to connecting hydraulic hoses correctly and applying specified torque values to fasteners. New O-rings should be coated with clean hydraulic oil before installation. After the control valve is installed, the cowl wiring harness must be connected, and the pedal assembly reinstalled with adhesive compound and proper torque. Finally, the dashboard, seal plate, kick panel, and floor plate are reinstalled, and calibration procedures must be performed.
Overall, this manual emphasizes safety, meticulous cleaning, precise assembly, and adherence to torque specifications to ensure the reliable and safe operation of the Hyster forklift's main control valve and hydraulic system.
General| Model | H4.0FT6 |
|---|---|
| Category | Forklifts |
| Load Capacity | 4000 kg |
| Lift Height | 3155 - 6500 mm |
| Mast Type | 2-Stage, 3-Stage |
| Rated Capacity | 4000 kg |
| Tire Type | Pneumatic |
| Engine Type | Diesel |
| Power Type | Internal Combustion |
| Overall Length | 2975 mm |
| Overall Width | 1450 mm |
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