hydraulics Flashcards
Pascal’s Law states that:
that pressure applied to any part of a confined liquid is transmitted with undiminished intensity to every other part
Some of the properties and characteristics that must be considered when selecting a satisfactory liquid for a particular system are:
Viscosity
Chemical stability
flash point
The three principal categories of hydraulic fluids are:
Minerals
Polyalphaolefins
Phosphate esters
What is the Mil spec number for Mineral oil-based hydraulic fluid?
Petroleum MIL-H-505
What colour is it dyed?
Red
What type of seals are used with petroleum-based fluids?
Synthetic rubber seals
Should an aircraft hydraulic system be serviced with the wrong type fluid?
Immediately drain and flush the system and maintain the seals according to the manufacturer’s specifications.
What are the two general contaminants?
Abrasives
Nonabrasive
When should a check of the system be made?
Whenever it is suspected that a hydraulic system has become contaminated or the system has been operated at temperatures in excess of the specified maximum
Fill out sample identification label supplied in sample kit, making sure to include customer name,
aircraft type, aircraft tail number, hydraulic system sampled, and date sampled. Indicate on the sample label under remarks if this is a routine sample or if it is being taken due to a suspected problem.
What provides adequate control of the contamination during hydraulic system operations?
Filters
Where are filters placed in the system to control particulate contamination?
in the pressure line
What hydraulic fluid can dissolve away some of the fatty materials of the skin?
Phosphate esters
What PPE should be worn when handling any type of hydraulic fluid?
Proper gloves and eye protection
A basic system consists of a:
Pump
Reservoir
Directional valve
Check valve
Pressure relieve valve
Selector valve
Actuator
Filter
Describe an open centre Hydraulic system:
An open centre system is one having fluid flow, but no pressure in the system when the actuating mechanisms are idle.
Describe a closed-centre system.
In the closed-centre system, the fluid is under pressure whenever the power pump is operating.
An advantage of the open-centre system over the closed-centre system is:
Continuous pressurisation of the system is eliminated.
An advantage of the closed-centre system over the open-centre system is:
. Pressure is available the moment the selector valve is positioned.
What are Power boost systems?
Power boost systems help the pilot in overcoming high control forces, but the pilot still actuates the flight controls with push rod or cable
What are power supply systems and fly-by wire flight controls?
They are the electric system for modern in which the pilot sends input to the flight control servos.
Advantages of Small power packs
there is no need for a centralized hydraulic power supply system and long stretches of hydraulic lines, which reduces weight.
What is the purposes of a reservoir:
The reservoir not only supplies the operating needs of the system, but it also replenishes fluid lost through leakage.
What types of gauges are used to attain reservoir level/quantities?
Visual gauge indicate the quantity
What does the filler strainer (finger strainer) do?
to prevent the entry of foreign matter during servicing
What is the advantage of using s quick disconnect service port?
This method reduces the chances of contamination of the reservoir.
How do you get the correct results when the hydraulic fluid quantities are checked or the reservoirs are to be filled?
The airplane should be in the correct configuration
Describe a filter.
A filter is a screening or straining device used to clean the hydraulic fluid, preventing foreign particles and contaminating substances from remaining in the system.
What happens if the filter becomes blocked?
Contamination in your hydraulic system
What types of filter element can you get?
Macron, porous metal or magnetic type
What is the micron element designed to prevent the passage of solids greater than?
10 microns
When replacing filter elements, what should you be sure of?
ensure that the sealing element in the filter assembly is intact.
What is the purpose of the bypass relief valve in a filter?
The bypass relief valve opens if the filter clogs, permitting continued hydraulic flow and operation of aircraft systems.
How can you monitor the condition of installed filter elements?
by measuring the drop in hydraulic pressure across the element under rated flow conditions.
What does the red indicator popping out signify?
That the element has been cleaned
Power-driven pumps are the primary source of energy and may be either:
engine driven, electric motor driven, or air driven.
What are Hand pumps generally installed for?
for testing purposes, as well as for use in emergencies
Modern aircraft use a combination of:
Modern aircraft use a combination of engine-driven power pumps, electrical-driven power pumps, air-driven power pumps, power transfer units (PTU), and pumps driven by a RAT (Ram Air Turbine).
What component is required when a constant displacement pump is used in a hydraulic system in which the pressure must be kept at a constant value?
pressure regulator
What type of pump is a gear-type power pump?
Constant-displacement
What is the purpose of Pump drive couplings?
Designed to serve as safety devices
What 2 types of pumps can Piston pumps be?
Constant displacement
Variable displacement
How does the shear section of the drive coupling work?
preventing damage to the pump or driving unit
Describe a variable-displacement pump:
A variable-displacement pump has a fluid output that is varied to meet the pressure demands of the system. The pump output is changed automatically by a pump compensator within the pump.
What type of pump is a vane-type power pump?
Consistent-displacement pump
What is the function of the flow control valves?
Control the speed and/or direction of fluid flow in the hydraulic system.
What is the purpose of a selector valve?
A selector valve is used to control the direction of movement of a hydraulic actuating cylinder or similar device.
What are the two main types of selector valves?
open-centre
closed-centre
How are most selector valves controlled?
mechanically, manually, electrically, hydraulically, or pneumatically
Describe a check valve:
Is a type of flow control valve in aircraft hydraulic systems allows fluid to flow unimpeded in one direction, but prevents or restricts fluid flow in the opposite direction.
What is an integral check valve?
When part of a component, the check valve is said to be an integral check valve.
What does an arrow on the outside of the housing indicated?
It indicates the direction in which the fluid flow is permitted
What does orifice check valves allow?
Full fluid flow in one direction and restricted flow in the other direction
What do quick disconnect valves installed in hydraulic lines prevent?
Loss of fluid when units are removed
List the types/purpose of automatic pressure control valves:
Some of them are an escape for pressure that exceeds a set pressure; some only reduce the pressure to a lower pressure system or subsystem; and some keep the pressure in a system within a required range.
Why is a pressure relief valve necessary?
It is used to limit the amount of pressure being exerted on a confined liquid. This is necessary because to prevent failure of components or rupture of hydraulic lines under excessive pressures. The pressure relief valve is, in effect, a system safety valve.