190301a Flashcards
What is the primary function of a hydraulically controlled machine?
To perform useful work
Define work
Force acting through distance
How do you find force using a formula?
Multiply pressure and moving area together
(Newtons X meters squared)
What are the disadvantages of hydraulic control?
- Fluids under pressure are dangerous
- noises produced
- oil leakage is a source of contamination and fire
- temperature variations affect reliability
- air trapped in the system can produce poor operation and damage
- they can easily operate inefficiently
Describe force
Force is the push or pull that is capable of producing or changing the motion of a body
As well as produce or change the motion of a body what else can force do?
Force must also be generated to retard or stop motion
What are some types of energy?
Mechanical, hydraulic, heat, electrical, chemical, light, and sound
What is energy? Define it
The ability to perform work usually in BTUs or Jules
What advantages does hydraulic control have?
- Relatively compact
- powerful but light
- flexible installation
- cooling and lubrication system is easy to accommodate
- provides precise accurate and smooth implement positioning
- easy to protect from overload conditions
Briefly describe potential energy
Energy that is stored in a body or substance
If a spring is compressed is it considered __________ energy
Potential
The law of conservation of energy states that energy cannot be __________ or ___________
Created or destroyed
In an engine is combustion chamber is it true that chemical energy is turned into heat energy?
Yes it is true heat energy is created in the engine combustion chamber
On an engine where is the mechanical output?
The flywheel
What is considered wasted energy in an engine?
Heat and noise
What type of waste energy does a hydraulic system have?
Heat energy
What two states does energy exist in?
Kinetic and potential
What does rate of oil flow have to do with the motion of our implements?
The rate of flow affects the speed of our implements
What does potential energy always want to do?
Change to kinetic energy
What is a good example of a potential energy storage in a hydraulic system?
An accumulator
For our purposes do we consider oil or fluid compressible?
No
A pressure difference shows a difference in potential energy what is it also called?
Pressure drop
Bernoulli’s principle states what?
As velocity of a fluid decreases the pressure exerted by the fluid increases
What did Bernoulli discover about constant flow’s and horizontal tubes?
The sum of the potential (pressure) and kinetic (rate of oil flow) energy would remain constant at any point along the length of the tube
Is the velocity of liquid greater or less or in a small section compared to a wider section of pipe?
The velocity of a liquid in a small section is greater compared to the wider section
If you demand more force and speed what is required?
greater power requirements
What is the formula to find pressure?
Force divided by area
Pressure = Force/ Area
What is the formula to find flow rate?
Flow rate equals cylinder volume divided by time
Flow rate = cylinder volume / time
What does flow rate determined in our cylinders?
Speed, the time required to raise load
What type of measurement do we use to represent the amount of power that a cylinder must produce in order to raise a load in a specific time?
kW
Kilowatts
What do we compare to find hydraulic system efficiency?
Output power is compared to the input power to drive the system
What form of power losses can we have?
Pressure losses and flow losses
Are hydraulic systems 100% efficient?
No
What can affect laminar flow?
Abrupt changes in directions , abrupt changes in cross-section, conductors too small
What must exist to allow flow to occur?
There must be a difference in potential energy
What do we gain in laminar flow?
Lower fluid velocity and turbulence which result in a lower pressure loss and heat generation
What does insufficient internal volume result in?
Excessive fluid velocity
Disrupting laminar flow creates what?
Turbulence
Describe backpressure?
Pressure created by resistance to flow on the return side of a system or component
Is internal leakage a good thing or bad thing?
Good thing if it is not excessive?
What does good internal leakage do?
Provides lube, seals and supports
What causes internal clearances to increase?
Wear
