Details

Introduction
The Hydraulic Refilling Trolley (model HST 300U) is a mission-critical piece of ground support equipment (GSE) engineered for rapid, reliable servicing of military aircraft hydraulic systems. Designed to meet the stringent requirements of fighter jets, transport aircraft, and helicopters, the HST 300U enables maintenance crews to pressurize, de-aerate, filter, and transfer hydraulic fluid in a single mobile unit. Its integrated pressurization (nitrogen-driven), vacuum de-aeration, and high-pressure filtration subsystems ensure contaminant-free delivery of hydraulic oils such as OM-15, DTD-585, and MIL-H-5606, safeguarding system integrity and extending component life.

Design Overview
- Chassis & Mobility: A robust welded tubular frame (40×40×4 mm and 75×40×5 mm sections) supports a dual-chamber SS304L reservoir (2×70 L) and all ancillary equipment. Four puncture-proof pneumatic tires, including two swivel casters, allow manual maneuvering and towing up to 15 mph (≈24 km/h) on apron surfaces.
- Modular Plumbing: Quick-disconnect aircraft adapters and JIC-style couplings simplify hook-up, while color-coded, braided-steel hoses resist kinking and abrasion. An ergonomic hose reel ensures tidy stowage and easy deployment.
- Control Panel: Centralized gauge cluster and selector switches give operators precise control over flow (up to 100 L/min per system) and pressure (up to 300 bar), with digital readouts for vacuum level (to 200 mbar abs.) and tank level.
- Environmental Resilience: All wetted components and enclosures are powder-coated and rated for –20 °C to +55 °C operation, with IP54 protection against dust ingress and water spray.

Key Features
- Dual-System Capability: Independently service two hydraulic circuits simultaneously, reducing aircraft downtime during depot-level maintenance.
- Vacuum-Based De-Aeration: An engine-driven vacuum pump extracts dissolved air and moisture to <200 mbar abs., preventing cavitation and hydraulic lock during subsequent system operation.
- Precision Pressure Control: Panel-mounted relief valves and selector switches allow step- wise adjustment of system pressure (increments of ±1 bar) and flow regulation via needle valves, ensuring safe topping of delicate actuators.
- High-Efficiency Filtration: 3 μm absolute filters arranged in bypass and mainline configurations remove particulates and varnish, delivering ISO 4406 cleanliness levels of 18/16/13 or better.
- Integrated Compressed Air Supply: A built-in compressor delivers instrument-quality air at 7 bar for pneumatic tools or auxiliary pressurization tasks, with moisture separators and coalescing filters to protect valves and seals.
- Safety Systems: Redundant relief and safety valves on both gas and fluid circuits vent to atmosphere if pressures exceed set thresholds (nitrogen: 180 bar; hydraulic: 350 bar). Over-temperature shutdown and emergency-stop buttons protect both equipment and personnel.

Main Hydraulic & Pneumatic Components
- Reservoir & Cylinders: Twin-chamber SS304L oil tank (2×70 L) with internal baffles for surge control; Nitrogen cylinder carriage (2×50 L bottles, 220 bar service pressure).
- Filtration & De-Aeration: Primary 3 μm high-pressure filters (one per system); Vacuum de-aeration module with diaphragm pump and oil mist eliminator.
- Valves & Regulators: Panel-mounted pressure reducers (0–300 bar) and needle valves for flow tuning; Solenoid-actuated isolation valves for automated sequencing.
- Gauges & Indicators: Dual 100 mm glycerine-filled pressure gauges (0–400 bar range); Sight-glass level indicator with 5 L gradations.
- Hoses & Reels: Two 10 m × 1⁄2′′ braided-steel hydraulic hoses with quick-release aircraft adaptors; Heavy-duty spring-retract hose reel with adjustable tension.

Technical Specifications

  

    

      
Parameter
      
Specification
    
  
  

    

      
Dimensions (L×W×H)
      
1,600 × 1,000 × 1,200 mm
    
    

      
Weight (Empty/Full)
      
320 kg / 445 kg
    
    

      
Oil Capacity
      
140 L (2×70 L chambers)
    
    

      
Nitrogen Supply
      
2×50 L @ 220 bar
    
    

      
Max Hydraulic Pressure
      
300 bar continuous; 350 bar relief
    
    

      
Flow Rate
      
100 L/min per circuit
    
    

      
Vacuum Level
      
Down to 200 mbar abs.
    
    

      
Air Supply
      
7 bar @ 100 L/min
    
    

      
Filtration Rating
      
3 µm absolute
    
    

      
Temperature Range
      
–20 °C to +55 °C
    
    

      
Mobility
      
Towable at 24 km/h; manual at <5 km/h
    
    

      
Protection
      
IP54 enclosure
    
    

      
Standards
      
MIL-STD-810G; ISO 11120 (gas cylinders); ISO 4406 (fluid)
    
  


Applications
- Aircraft Hydraulic Servicing: Topping off actuators, reservoirs, and auxiliary systems on SU-30 MKI, C-17 Globemaster, and AH-64 Apache platforms.
- Hydraulic Test Benches: Pre-commissioning, flushing, and validation of ground-based hydraulic test rigs.
- Field & Expeditionary Use: Rapid deployment in forward operating bases and austere environments for emergency repairs and maintenance.
Safety & Compliance
- Over-Pressure Protection: Dual relief valves and burst discs on both gas and hydraulic circuits, venting to safe zones.
- Environmental: Conforms to IP54 for dust/water ingress; operates in –20 °C to +55 °C ambient conditions.
- Regulatory: Cylinders certified per ISO 11120 and ADR for road transport; hydraulic components meet MIL-STD-810G shock and vibration criteria.
- Operator Training: Comprehensive user manual and on-site training ensure adherence to maintenance schedules (filter change every 500 hours; vacuum pump service every 1 000 hours).

Conclusion
By combining high-pressure nitrogen drive, precision vacuum de-aeration, and multi-stage filtration in a nimble, towable platform, the HST 300U Hydraulic Refilling Trolley sets the benchmark for aircraft hydraulic servicing. Its modular design, adherence to military and aerospace standards, and user-friendly controls make it indispensable for MRO operations, reducing turnaround times, minimizing fluid waste, and enhancing system reliability across a wide array of platforms.