Hydaulic Priciple Alberta Moduals Flashcards
Hydraulic systems do what?
Transmit power
The output unit in a hydraulic system is referred to as a?
Actuator
Cylinder or hydraulic motor
How does a hydraulic system transmit power?
Pressurized liquid
What are the components you must work with in a hydraulic system?
-Reservoir
-Pump that produces flow
-Various pipes, tubes, and hoses
-Valves that control the direction, speed and pressure of the fluid
-actuator that does the work
How much does hydraulic oil compress when the pressure is at 1000psi?
1/2%
Fluid in 8’pipe will compress 1/2” at 1000psi before it will lift a cylinder
Pressure conversion chart
Describe a 2-1 cylinder?
When the cross section of the rod occupies exactly half the area of the piston on the rod end side.
How is flow expressed?
Flow is expressed in either velocity(speed) feet/min or feet/second
Or
Flow rate in gallons/min or cubic inches/min
When calculating flow what must you always do?
Calculate every thing into the proper units first.
What is the 231 trick?
To convert gallons/minute to cubic inches a minute multiply 231 to you number of us gallons.
231 x (# of us gallons) = cubic inches/min
How do you find the area of a circle?
.7854 X Diameter squared
A regenerative circuit is designed to provide equal speed and force when the cylinder extends and retracts. To achieve this you need a _______ cylinder.
How does it work?
2-1 cylinder
Why can reducing the pipe size in a hydraulic system be bad?
Because it can drastically increase the speed of fluid which waste a lot of energy, Robs pressure and wears out components
What are the recommended maximum velocities in a hydraulic system?
The amount of friction in laminar flow _______ as velocity increases?
Increases
Laminar flow Vs turbulent flow
(Study chart)
Conditions for laminar and turbulent flow
(See chart)
How is cavitation recognizable?
Immediately recognizable by rattling sound and confirmed by abnormally low pressure at the pump inlet
What are the effects of cavitation?
- very rapid erosion of metal surfaces
- severe pump damage
- generation of high frequency damage
- flow reduction
- erratic operation of valves and actuators
- accelerated fluid oxidation
- interference with lubrication of the components
What are the causes of cavitation?
Although very similar characteristics what is the difference between aeration and cavitation?
Cavitation is caused by the violent collapse of gas bubbles. The cause of cavitation originate from gasses being dissolved in hydraulic fluid
Aeration occurs when air becomes mixed with the fluid. The process begins with site leaking into the system through inadequate sealing or air becoming entrapped on the system during maintenance
Causes of aeration?
Pascals law applies only to fluid at rest. What principle applys when the fluid starts to move?
Bernoulli’s principle notes that pressures in the system vary with the velocity of the flowing fluids.
As velocity of fluid increases the pressure decreases. When pressure increases the velocity decreases.
Bernoulli’s principle does not take _______ into account?
Energy losses due to friction
In the real world you must add losses caused by friction
What is the common imperial unit of work?
Foot pound
A force of one foot pound is applied to move an object a distance of one foot.
Describe power?
The rate at which work is done
If you move an object very quickly over a distance of one foot you use more power than if you move the same object with the same force over the same distance slowly .
1hp = 33000 foot pounds/second how many foot pounds/minute?
Divide by 60
550 foot pounds per minute
What are the two types of efficiency in a hydraulic system?
Power efficiency
And
Volumetric efficiency
If efficiency is low consider what two possibilities?
System has been maintained properly
Then
Check how the system was designed.
Example, is flow always flowing through relief valve
What is volumetric efficiency?
A measure of how much fluid an actuator or pump discharges in comparison to the amount of fluid intake.
What is the difference between an open loop system and a closed loop system?
An open loop system the return line does not connect directly to the pump inlet.
A closed loop system the return lines hook directly to the pump
What is the purpose of a charge pump?
To return the fluid from the case drains back to the inlet of the Main pump. The us known as a hydrostatic drive (closed loop)
What are the different symbols for conductors?
What is a tube symbol?
What is the hose symbol?
What does the open tank reservoir indicate?
The reservoir is vented to atmosphere. Allowing for atmospheric pressure to push the fluid into the pump inlet where there is partial vacuum
Why is a inlet filter installed? And is it a coarse or fine filter?
To protect the pump.
It is a course filter to remove large particles or small objects that may damage the pump.
If the filter is to fine it will restrict flow to the pump
Why is the return line filter so important?
It captures any wear debris generated in the system or contaminants that may have been introduced when new fluid was installed.
Very fine filter, does not restrict flow as much because the fluid is at its hottest point.
What is the purpose of the pump in a hydraulic system?
To make fluid flow. It is drive by the prime mover (electric motor for stationary and internal combustion engine for mobile systems)
Where is the maximum pressure relief valve always located?
Directly after the pump and is the first valve in the system.
When you set the pressure on the pressure relief valve, you are setting the ____________ the cylinder exerts?
Maximum