Basic Hydraulic Systems - Hydraulics - Airframes & Aircraft Systems #6
Summary
TLDRThis lesson introduces the components of a basic hydraulic system, focusing on the open center and closed systems used in aircraft. The open center system, suitable for light aircraft, allows only one service at a time and operates with a pump that runs in an offloaded condition. In contrast, the closed system, common in large aircraft, enables multiple services simultaneously and maintains operating pressure. Key components include a reservoir, pump, selector valves, actuators, filters, and a relief valve. The lesson also explains hydraulic lock and the operation of pumps in both systems.
Takeaways
- 🔧 Most aircraft hydraulic systems are active, with a pump supplying pressure, unlike the passive Brahma press system.
- 💧 There are two main types of active hydraulic systems: open center and closed center systems.
- 📦 The six main components of hydraulic systems are reservoir, pump, selector or control valves, actuator, filters, and relief valve.
- 🚀 The open center system is simpler and used in light aircraft, but it can only operate one service at a time.
- 🔄 In the open center system, fluid flows through selector valves in sequence until it reaches the last valve, then returns to the reservoir.
- 🛠️ The relief valve in the open center system is crucial for relieving excess pressure if the selector is not returned to neutral.
- 🔑 The closed system is used in large aircraft and allows multiple services to operate simultaneously, limited only by the pump's volume flow capacity.
- 🔄 In closed systems, operating pressure is maintained, and mechanisms like automatic cutout valves or variable volume pumps prevent pump overload.
- 🔒 The hydraulic lock in closed systems locks fluid on both sides of the actuator, preventing any uncommanded movement.
- 🔌 Some light aircraft use a hydraulic power pack with an electrically driven pump and an accumulator for simpler hydraulic operations.
Q & A
What are the two types of basic hydraulic systems mentioned in the script?
-The two types of basic hydraulic systems mentioned are the open center system and the closed system.
What is the main disadvantage of the open center hydraulic system?
-The main disadvantage of the open center hydraulic system is that only one service can be operated at a time.
What are the six main components common to both open center and closed hydraulic systems?
-The six main components common to both systems are a reservoir of oil, a pump, selector or control valves, actuators, filters, and a relief valve.
How does the fluid flow in an open center hydraulic system when no service is operating?
-In an open center hydraulic system, if no service is operating, the fluid flows from the pump through the pressure filter to the selector valve, then through the central port to the next selector valve, and this can continue for as many valves as required, finally returning to the reservoir.
What happens when a user system is selected in an open center hydraulic system?
-When a user system is selected, the fluid is directed to the actuator, which moves, and the fluid from the other side of the actuator returns to the reservoir via the central port of the selector valve.
What is the purpose of the relief valve in a hydraulic system?
-The relief valve relieves excess pressure if the selector is not returned to its neutral position.
Why is the closed hydraulic system used on almost all large aircraft?
-The closed hydraulic system is used on almost all large aircraft because it allows multiple services to be operated at the same time, limited only by the volume flow capacity of the pump.
How does the closed system prevent overloading the pump?
-In systems with a fixed volume, constant delivery pump, an automatic cutout valve is used to divert pump output to the reservoir when pressure has built up to normal operating pressure. In other systems, a variable volume, constant pressure pump is used, which automatically reduces delivery flow as pressure increases.
What is the significance of returning the selector valve to neutral in a closed hydraulic system?
-In a closed hydraulic system, it is not as critical to return the selector valve to neutral once the operation is complete, as the pump control system is designed to handle the pressure increase. However, returning the selector valve to neutral creates a hydraulic lock across the actuator, preventing any uncommanded movement.
What is a hydraulic lock and why is it important?
-A hydraulic lock occurs when the fluid is locked in on both sides of the actuator, preventing any undemanding movement because the fluid is incompressible. It is important for maintaining the position of the actuator and ensuring stability.
Outlines
🔧 Introduction to Basic Hydraulic Systems
This paragraph introduces the components of a basic hydraulic system and the two types of systems in common use: open center and closed systems. It explains that most aircraft hydraulic systems are active, requiring a pump to supply pressure. The paragraph details six main components shared by both systems: a reservoir of oil, a pump, selector or control valves, actuators, filters, and a relief valve. It then describes the operation of the open center system, which can only operate one service at a time, and how fluid flows through the system until it returns to the reservoir. The relief valve's role in relieving excess pressure is also mentioned. This system is popular in light aircraft due to its simplicity and the intermittent need for hydraulic power.
🛫 Open Center vs Closed Hydraulic Systems
The second paragraph contrasts the open center and closed hydraulic systems. It emphasizes the closed system's ability to operate multiple services simultaneously, limited only by the pump's volume flow capacity. The paragraph explains how the closed system maintains operating pressure and uses mechanisms like automatic cutout valves or variable volume pumps to prevent overloading. It also describes the operation of services in the closed system, where selector valves control the flow to actuators and the importance of returning the selector valve to neutral to create a hydraulic lock, preventing any unwanted movement of the actuator. The paragraph concludes by mentioning the use of hydraulic power packs in simple light aircraft systems, which include an electrically driven pump, a pressure-operated switch, and an accumulator to control the system's operation.
Mindmap
Keywords
💡Hydraulic System
💡Open Center System
💡Closed System
💡Pump
💡Selector Valve
💡Actuator
💡Reservoir
💡Filter
💡Relief Valve
💡Hydraulic Lock
💡Pressure
Highlights
Introduction to the components of a basic hydraulic system.
Differentiation between passive and active hydraulic systems, with the Brahma press as an example of a passive system.
Explanation of the two types of active hydraulic systems: open center and closed systems.
Identification of the six main components common to both hydraulic systems.
Description of the open center system's operation and its limitation to one service at a time.
Mechanism by which fluid flows through selector valves in an open center system.
The role of the relief valve in managing excess pressure in an open center system.
Advantages of the closed hydraulic system, allowing multiple services to operate simultaneously.
How the operating pressure is maintained in the closed system and methods to prevent pump overloading.
Comparison between fixed volume constant delivery and variable volume constant pressure pumps.
Operation of services in a closed system, highlighting the ability to operate multiple services at once.
Importance of returning the selector valve to neutral in closed systems for hydraulic lock.
Definition and function of hydraulic lock in preventing uncommanded movement of actuators.
Use of hydraulic power packs in simple light aircraft systems for controlled service operation.
Explanation of how an accumulator works in a hydraulic power pack to maintain pressure.
Summary of the differences between open center and closed hydraulic systems.
Emphasis on the closed system's advantage of simultaneous service operation.
Transcripts
in this lesson you will learn about the
components that make up a basic
hydraulic system and how the two types
of basic system operate
you
the Brahma press was as previously
mentioned a passive hydraulic system
however apart from light aircraft brakes
which is of little practical use to us
most aircraft hydraulic systems are
active systems where a pump supplies the
pressure
there are two types of active hydraulic
system in common use they are known as
the open center system and the closed
system
there are six main components common to
both systems a reservoir of oil
a pump
selector or control valves
later or actuators
filters
and a relief valve
we will begin by explaining how the
components of the two basic systems
integrate with each other then in later
lessons describe the various components
in greater detail
the simplest hydraulic system used in
aircraft is the open center system its
main disadvantage is that only one
service can be operated at a time fluid
flows from the pump through the pressure
filter to the first selector valve
if the service connected to this valve
is not operating then the valve will be
in the position shown and the fluid will
flow through the central port to the
second selector valve
if this service doesn't require fluid
then this valve will also be in the
position as shown and again the fluid
will flow through the central port
this can continue for as many valves as
required
when the fluid passes through the last
valve in the sequence it returns to the
reservoir this allows the engine driven
pump to run in an offloaded condition as
little pressure is generated but there
is still a flow of oil through the pump
to cool and lubricated
on selection of a user system
the fluid is directed to the actuator
which will move
the fluid from the other side of the
actuator will return to the reservoir
via the central port of the second
selector
when the actuator reaches the end of its
travel the selector is returned to
neutral in order to offload the pump and
allow other services to be selected
the relief valve will relieve excess
pressure if the selector is not returned
to its neutral position
this type of system is popular in many
light aircraft which do not require a
constant pressure to be maintained all
the time only items such as landing gear
and flaps will be powered for short
periods of time on each flight
the closed system is used on almost all
large aircraft it's great advantage
being that multiple services can be
operated at the same time their use is
only limited by the volume flow capacity
of the pump
with this system operating pressure is
maintained in that part of the system
which leads to the selector valves and
some method needs to be used to prevent
overloading the pump
in systems which employ a fixed volume
constant delivery pump an automatic
cutout valve is fitted to divert pump
output to the reservoir when pressure
has built up to normal operating
pressure
in other systems a variable volume
constant pressure pump is used this type
of pump automatically reduces delivery
flow as pressure increases
we will examine both of these pumps in
greater detail in the lesson on pumps
operates its services in the same way as
the open Center system the selector
valve is moved opening up pressure and
return lines to the required service
however there are two important
differences
firstly as shown here two or more
services can be operated at the same
time
and secondly it is not so important to
return the selector valve to neutral
once the operation is complete as the
pump control system is designed to deal
with the consequent pressure increase
nonetheless in most systems the selector
valve is returned to neutral as this
performs the important function of
producing what is known as a hydraulic
lock across the actuator what this means
is that the fluid is locked in on both
sides of the actuator consequently
because the fluid is incompressible the
actuator will not be able to produce any
undemanding movement
in some simple light aircraft systems a
hydraulic power pack is used this
consists of an electrically driven pump
which is controlled by a pressure
operated switch with an integral
reservoir and an accumulator
when the service is selected pressure
will drop causing the accumulator piston
to move up switching on the pump
the pump will operate until the service
reaches its required position and the
accumulator is repressurized
when it will be automatically switched
off again
you should now understand the
differences between the open center and
closed hydraulic systems
bear in mind that the big advantage of
the closed system is that two or more
services can be operated simultaneously
whilst in the open center system you are
limited to operating one service at a
time
[Music]
you should now also understand the
meaning of the term hydraulic lock
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