Hydraulic Systems and Components

Overview of Hydraulic Components

• This lesson focuses on hydraulic valves and actuators, continuing from the principles of hydraulics discussed in the previous lesson.

Types of Valves and Their Functions

• Pressure Relief Valves (PRV) and Thermal Relief Valves (TRV):

  • Protect the system from overpressure.
  • Allows fluid to return to the reservoir when the pressure exceeds a preset limit.
  • Functionality involves a ball valve held in place by a spring, adjustable for cracking pressure.
  • PRV can also act as a TRV to relieve pressure from thermal expansion when fluids are heated (e.g., from sunlight).
  • Cracking pressure is the point at which the valve opens to release excess pressure.

• Non-Return Valves (Check Valves):

  • Allows flow in one direction only, using a ball held by a spring.
  • Prevents backflow, ensuring fluid flows only towards its intended destination.

• Shuttle Valves:

  • Direct fluid from one of two possible supply routes based on pressure.
  • Automatically switch to a backup system if the primary pressure fails to maintain service continuity.

• Flow Restrictors and Chokes:

  • Control flow rates to manage the speed of hydraulic operations.
  • Example: full flow for raising landing gear vs. restricted flow for lowering it using gravity.

• Throttling Valves:

  • Regulate flow to ensure constant speed operation of hydraulic motors.
  • Maintain low input pressure while providing constant output pressure regardless of input pressure changes.

• Pressure Reducing Valves:

  • Lower pressure for subsystems (e.g., brakes) while maintaining higher pressure for critical components (e.g., flight controls).

• Sequencing Valves:

  • Ensure operations occur in a defined sequence (e.g., opening landing gear doors before lowering landing gear).
  • Allow only one service to operate at a time, preventing mechanical damage.

• Hydraulic Fuses:

  • Protects against fluid loss due to leaks by shutting off flow to the affected service.

• Modulators:

  • Used in anti-skid systems to control brake pressure with rapid feedback for optimal braking performance.

• Priority/Pressure Maintaining Valves:

  • Prioritize critical services (like flight controls) over non-essential ones when pressure is low.

Managing Hydraulic Fluid Temperature

• Heat Exchangers:

  • Used to cool hydraulic fluid while providing warmth to fuel, preventing wax and freeze issues at high altitudes.

• Temperature Monitoring:

  • Monitored in the cockpit; abnormal temperatures may affect fluid viscosity and, thus, system performance.

Filtration and Circuit Protection

• Filtration:

  • Essential for removing solid contaminants (25 microns or larger) to protect hydraulic components.
  • Usually done with full flow micronic pressure filters fitted downstream of the pump.
  • Indicators alert if the filter is clogged and bypass mechanisms ensure fluid flow even with clogged filters.

• Shut Off Valves:

  • Installed for safety (e.g., in case of an engine fire or pump failure) to quickly stop fluid flow.

Summary of Safety Mechanisms

• Quality through filtration
• Safety ensured by pressure relief valves
• Flow bypass for unfiltered fluid through blocked filters
• Shut off valves for emergency scenarios

In summary, the hydraulic systems are equipped with various types of valves and filtration systems to ensure safety, functionality, and efficiency. Understanding these components is crucial for effective operation and maintenance of hydraulic systems in aircraft.