Basic Hydraulic Systems - Hydraulics - Airframes & Aircraft Systems #6

Summary

This 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

00:00

🔧 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.

05:03

🛫 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.

Keywords

💡Hydraulic System

A hydraulic system is a method of transferring power in which a fluid, typically oil, is used to transmit force. In the context of the video, it refers to the systems used in aircraft to operate various mechanical devices such as landing gear and flaps. The video explains that there are two types of basic hydraulic systems: passive and active, with aircraft primarily using active systems where a pump supplies pressure.

💡Open Center System

The open center system is a type of active hydraulic system used in aircraft, characterized by its ability to operate only one service at a time. It is mentioned in the script as the simplest hydraulic system used in aircraft, where fluid flows sequentially through selector valves, and only if a service is selected does fluid get directed to the actuator. This system is popular in light aircraft due to its simplicity and the fact that it doesn't require constant pressure maintenance.

💡Closed System

A closed hydraulic system is another type of active system described in the script, which allows for multiple services to be operated simultaneously. This is in contrast to the open center system and is used in almost all large aircraft. The advantage of the closed system is that it can handle multiple services at once, limited only by the pump's volume flow capacity, which is crucial for large aircraft that require complex and simultaneous hydraulic operations.

💡Pump

In a hydraulic system, the pump is a device that moves fluids, typically oil, and supplies pressure. The video distinguishes between two types of pumps used in aircraft hydraulic systems: fixed volume constant delivery pumps and variable volume constant pressure pumps. The former uses an automatic cutout valve to prevent overloading, while the latter adjusts its delivery flow based on pressure changes, ensuring efficient operation.

💡Selector Valve

A selector valve is a component in hydraulic systems that directs fluid flow to the desired service or actuator. The script explains that in an open center system, fluid flows through selector valves in sequence, and only the selected service receives fluid. In a closed system, multiple services can be selected simultaneously, showcasing the valve's role in managing fluid distribution within the system.

💡Actuator

An actuator in a hydraulic system is the component that converts fluid pressure into mechanical movement. The script describes how, upon selection of a service, fluid is directed to the actuator, which then moves, performing the required function such as extending landing gear. The fluid from the other side of the actuator returns to the reservoir, completing the hydraulic cycle.

💡Reservoir

A reservoir is a storage container for the fluid, typically oil, used in hydraulic systems. As mentioned in the script, it is one of the six main components common to both open center and closed hydraulic systems. The reservoir serves to hold the fluid, which is then drawn upon by the pump to supply pressure to the rest of the system.

💡Filter

Filters in hydraulic systems are used to remove contaminants from the fluid to prevent damage to system components. The script specifies that fluid flows from the pump through a pressure filter before reaching the selector valves. This filtration process is crucial for maintaining system efficiency and longevity by ensuring clean fluid operation.

💡Relief Valve

A relief valve is a safety device in hydraulic systems that releases excess pressure to prevent damage to system components. The script explains its function in the open center system, where if a selector valve is not returned to its neutral position, the relief valve will activate to relieve the excess pressure, thus protecting the system from potential damage.

💡Hydraulic Lock

Hydraulic lock refers to a condition where fluid is trapped on both sides of an actuator, preventing any undesired movement. The script describes that in a closed system, returning the selector valve to neutral creates a hydraulic lock, which locks the fluid in place and ensures the actuator does not move unintentionally. This concept is important for maintaining the stability and safety of hydraulically operated components.

💡Pressure

Pressure in a hydraulic system is the force exerted by the fluid, which is essential for operating the system's components. The script discusses how pressure is supplied by the pump in active systems and how it is managed through selector valves and relief valves. Understanding pressure management is key to the proper functioning of hydraulic systems, as it directly affects the operation of actuators and the overall system performance.

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