301A: Hydraulic Principles Flashcards
List four advantages of hydraulic control in heavy equipment machinery
functions.
a) Relatively compact
b) Installation is more flexible than mechanical
c) Cooling and lubrication is easy to accommodate
d) Easily control several functions at one time
301A: Pg. 2
List four disadvantages of hydraulic control in heavy equipment machinery
functions.
a) Fluids under pressure can result in personal injury or death if not handled
safely.
b) There is always some noise produced by the system.
c) Oil leakage is a source of contamination and fire.
d) Temperature variations (too high or low) effect component reliability and
machine performance.
301A: Pg. 2
Work is defined as a:
Force acting through a distance
301A: Pg. 2
Force is the push or pull that is capable of producing or changing the motion of a body (T/F)
True
301A: Pg. 2
Energy is defined as:
The ability to do work
301A: Pg. 4
List four common forms of energy.
a) mechanical energy
b) hydraulic energy
c) heat energy
d) electrical energy
301A: Pg. 4
The law of conservation of energy states that:
Energy cannot be created or destroyed.
301A: Pg. 4
In an engine, chemical energy in the fuel is converted to mechanical energy in the
engine combustion chamber. (T/F)
False; Chemical energy in the fuel is converted to heat energy in the
combustion chamber.
301A: Pg. 4
A hydraulic actuator converts energy from what form to what form?
Hydraulic energy into mechanical energy.
Kinetic energy in a hydraulic system is created by:
The rate of oil flow through a system
301A: Pg. 5
Potential energy in a hydraulic system is responsible for creating:
a) force
b) motion
c) actuator speed
d) mechanical energy
a) Force
301A: Pg. 5
Laminar flow refers to:
When oil flows through a system in straight parallel flow paths.
List three conditions that could result in turbulent hydraulic flow
- Conductors that are too small
- Abrupt changes in conductor cross-section
- Abrupt changes in flow direction
301A: Pg. 10
Excessively turbulent flow in a hydraulic system will result in excessive:
Pressure losses (lost as heat)
301A: Pg. 10
Hydraulic actuators that are connected in series will have the same pressure applied to each actuator. (T/F)
False; Pressure applied to each actuator will vary while flow remains constant.
301A: Pg. 12
Actuators connected in series provide:
A) High torque, limited speed
B) High torque, high speed
C) Limited torque, high speed
D) Low power losses
C) limited toque, high speed.
Describe the pressure and flow characteristics of a hydraulic circuit that has multiple actuators connected in parallel.
a) Pressure characteristics are ________
b) Flow characteristics are__________
a) the same pressure is applied to each actuator.
b) the flow is split amongst the actuators.
Hydraulic fluids that have a low VI number:
have wide viscosity changes with temperature.
The oil characteristic that has the most significant effect on the oil’s lubricating
ability is:
viscosity.
Two (2) conditions that indicate that an oil is excessively oxidized are:
a) the oil will have a burnt odour.
b) the oil will have a watery feel.
State the two conditions that a hydraulic fluid must meet in order to be classified as biodegradable
a) 70 - 80% of the base fluid must be able to be broken down by micro-organisms.
b) The fluid must not harm living organisms.
Why is it a common service procedure to replace the hydraulic filter on a new piece
of machinery after about 100 hours of operation?
To remove built-in contamination from the system.
List four (4) entry points of ingressed contamination.
a) reservoir air breathers
b) pump inlet leakage
c) cylinder seals
d) unclean maintenance procedures.
A rapid total disabling of a system or component is known as an:
catastrophic failure.
Degradation failures are caused by _________
gradual surface wear.
What type of contamination comes from external sources?
Ingressed
What type of contamination could be drawn in by leakage at the pump inlet?
Air
Will hydraulic cylinder seals and wipers remove all fine contaminants from the rod as it retracts?
No
Particles larger than 10 µm (microns) will be brought into the system - ingressed contamination
What is internally generated contamination?
It refers to particles the break loose from internal surfaces of hydraulic components.
What are three types of failures of hydraulic components related to contamination?
- Catastrophic failure
- Intermittent failure
- Degradation failure
Small particles blocking a relief valve poppet could cause?
Relief valve to not move and resulting overpressure could sheer drive shafts or split pump housing’s
Why is it intermittent failure sometimes called transient failure?
Because the problem often moves from component to component. Often self-correcting which makes it difficult to troubleshoot
What is a characteristic of degradation failure?
It will result in excessive internal leakage and progress to catastrophic failure.
What is a synthetic fire resistant hyd fluid made up of?
It is made up of chemically remanufactured ester fluids. Most common is phosphate ester fluid.
Name the advantages synthetic fire resistant fluids have over water based.
They can operate at higher pressures.
They offer greatly improved lube qualities.
They are generally more fire resistant.
What 2 conditions must oil meet to be qualified as a bio oil by ISO standards?
1) 70-80% must be able to be broken down by micro organisms within a set period of time.
2) must not harm living organisms.
What is a problem with vegetable oils being used as a hydraulic fluid?
They oxidize rapidly when exposed to temps above 60c (140f)
There are some problems associated with ester hydraulic fluids, they are:
They produce acids that damage system components. Nitrile rubber must be replaced with Viton seals.
They react with metals in the system. Particularly zinc, brass and bronze.
Very expensive.
Proper hydraulic fluid should be chosen after considering:
Manufacturers specifications
Ambient conditions
Compatibility
There are many contaminants in a system, name some possibilities.
Foreign liquids - water and acids
Metallic particles - iron, steel, aluminum and brass
Non metallic particles - dirt, rubber, lint and flakes of paint
There are always contamination built into a system. T/F
True. This is why it is recommended that an oil change be done within a machines first 100 hours.
Two hydraulic motors are connected in parallel.The parallel circuit divides what between the two motors?
oil flow
Hydraulic oils can be divided into three general categories. They are:
- Petroleum-based
- Fire resistant
- Biodegradable
What is Bernoulli’s principle?
As the velocity of a fluid decreases the pressure exerted by the fluid increases
301A Pg. 7
What is the formula for pressure?
Pressure = force/area
What is the formula for flow rate
Flow rate = cylinder volume/time
What is the formula for hydraulic pump output horsepower?
Kw = L/min * MPa * 0.0167
Hp = (gpm * rpm) / 1714
How is hydraulic system efficiency determined?
By comparing the output power of a system to the power required to drive the system.
Efficiency of a pump = Actual output / Rated output
Greater than 80% efficiency is good for a pump
301A Pg. 9
Power loss in a hydraulic system is manifested through what two forms?
Pressure Loss
- From not having laminar flow and backpressure
Flow loss
- From designed and unintended internal leakage
301A Pg. 9
True or false
There must be a difference in potential energy in order for flow to occur in a hydraulic system
True
The greater the pressure lost in the system, the more _____ will be generated
Heat
Describe laminar flow
When oil moves through the system in straight parallel flow paths.
- Conductors of adequate size
- Smooth transition at bends/fittings
- Gradual changes in piping direction
301A Pg. 9
Most manufacturers recommend an oil VI of at least _____
90
301A Pg. 17
What is added to oil which develops a protective film on moving parts?
Anti-wear additives
301A Pg. 17
What is demulsification?
When water in oil separates out
