Views: 0 Author: Site Editor Publish Time: 2022-10-21 Origin: Site
The basic principle of aviation hydraulics is the use of pressurized fluid to move specific components from one location to another. The principle behind how hydraulic systems work is Pascal's Law. Simply put, a fluid under pressure exerts equal pressure in every point and every direction in the fluid.
The aircraft hydraulic system is a complex system that provides a way of controlling the operation of aircraft components. The most common applications of aircraft hydraulics are flight control surfaces, landing gear, thrust reversers and brakes. Before understanding a complex hydraulic system, you first need to understand the basic components of a simple hydraulic system.
The electric pump of the yellow hydraulic system is mainly used for ground maintenance and cargo door operation. If no power is available, the cargo door can be operated using the hand pump in the yellow system. The blue electric pump can be used as an auxiliary power source for ground maintenance.
The RAT is the auxiliary pressure source for the blue hydraulic system and emergency electric constant speed motor/generator (CSM/G). RATs are deployed automatically or manually based on failure conditions. It pressurizes the blue hydraulic system to 2500 psi. According to specific maintenance procedures, it can only be retracted on the ground.
The power transmission allows the green system to be pressurized by the yellow system and vice versa. It transmits hydraulic power, but not hydraulic oil. The PTU is an auxiliary pressure source for the green or yellow system, eliminating the need to transfer fluid between the two systems.
When the differential pressure between the green and yellow circuits is greater than 500 psi, the power transmission unit (PTU) will automatically operate.
A hydraulic filter is required to filter out any particles that may enter the hydraulic fluid. These particles can enter the system during maintenance or during wear on working parts. If these contaminants are allowed to remain in the circulating fluid. They can damage seals and cylinder walls, cause internal leaks, and prevent components such as check valves from seating properly.
HP Filter – A high pressure (HP) filter installed in the pressure line.
LP Filter – A low pressure (LP) filter installed in the return line.
Case Drain Filter – Installed in the case drain line pump cooling and lubrication.
All of these filters have a red clogging indicator that pops up when the filter is clogged (dirty) and the filter element can be replaced.
What is the purpose of an accumulator in a hydraulic system?
The accumulator acts as a shock absorber for small changes and can hold 1L of total oil when the accumulator is full. When multiple units are running simultaneously, the accumulator provides additional power from its accumulated or stored power to assist or supplement the power pump.
In low hydraulic conditions, the priority valve maintains basic system operation by cutting off hydraulic power to heavily loaded users. The priority valve threshold in the A320 aircraft hydraulic system is 1842 psi.
What are the conditions when PTU operation is disabled?
PTU operation of A320 aircraft is prohibited:
1. When the cargo door is operated,
2. If PTU P/B is closed,
3. When the air conditioner is on the ground and one engine is running, if the parking brake is on or the front wheel steering is disconnected for towing (eg: first engine start during push back).