190301a Flashcards
List four (4) advantages of hydraulic control of heavy equipment machinery functions.
a) Hydraulic components are relatively compact. They are powerful yet are
light in weight and generally occupy a small space.
b) Installation of a hydraulic system is much more flexible than mechanical
systems because components can be easily placed in the best position on the
machine.
c) Cooling and lubrication of system components is easy to accommodate.
d) The operator can easily control several functions at one time which increases
productivity.
List four (4) disadvantages of hydraulic control of 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.
Work is defined as a:
force acting through a distance.
Force is the push or pull that is capable of producing or changing the motion of a
body T/F
true
Energy is defined as?
Energy is defined as the ability to do work
List four (4) common forms of energy.
a) mechanical energy
b) hydraulic energy
c) heat energy
d) electrical energy
The law of conservation of energy states that
energy cannot be created or destroyed.
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.
A hydraulic actuator converts:
hydraulic energy into mechanical energy.
Kinetic energy in a hydraulic system is created by
the flow of oil through the system.
Potential energy in a hydraulic system is responsible for creating:
force.
A hydraulic cylinder that has a bore of 10 cm and a stroke of 4.25 m. How much
pressure (in MPa) is required to overcome a load of 2500 kg when the cylinder is
extending? Round off your answer to the nearest 2 decimal places.
3.12 MPa
If the cylinder described in question 12 has a rod diameter is 5.5 cm and a stroke
length of 4.25 m, what flow rate (in L/min) would be required to move the load from
the fully extended position to the fully retracted position in 7 seconds? Round off
your answer to the nearest 2 decimal places.
199.56 L/min
How much output power (measured in kW) must the cylinder produce to accomplish
the task described in question 13? Round off your answer to the nearest 2 decimal
places.
14.89 kW
Laminar flow refers to
flow that moves in straight parallel flow paths.
List three (3) conditions that could result in turbulent flow.
. a) Installing conductors that are too small.
b) Abrupt changes in conductor cross-section.
c) Abrupt changes in flow direction.
Excessively turbulent flow in a hydraulic system will result in excessive:
pressure losses.
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.
Actuators connected in series provide:
limited toque but 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.
Which of the following hydraulic fluids is NOT a fire resistant fluid?
petroleum-based fluid
State the two (2) 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 through ingress contamination
What is internally generated contamination?
It refers to particles the break loose from internal surfaces of hydraulic components.
Internally generated particles come from where?
Possibly every component in the system.
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 syn 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 an ester?
In chemistry, esters are chemical compounds derived from an acid (organic or inorganic) in which at least one -OH (hydroxyl) group is replaced by an -O-alkyl (alkoxy) group.[1] Usually, esters are derived from a carboxylic acid and an alcohol. Glycerides, which are fatty acid esters of glycerol, are important esters in biology, being one of the main classes of lipids, and making up the bulk of animal fats and vegetable oils. Esters with low molecular weight are commonly used as fragrances and found in essential oils and pheromones. Phosphoesters form the backbone of DNA molecules. Nitrate esters, such as nitroglycerin, are known for their explosive properties, while polyesters are important plastics, with monomers linked by ester moieties.
What is a problem with vegetable oils being used as a hyd fluid?
They oxidize rapidly when exposed to temps above 60c (140f).
There are some problems associated with ester hyd 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 hyd 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
What type of equipment would we see a series-parallel hydrulic circuit in?
Automatic two speed skid steer
Hydraulic oils can be divided into three general categories. They are:
- petroleum-based hydraulic fluids,
- fire resistant hydraulic fluids and
- biodegradable hydraulic fluids
What is Bernoulli’s principle?
Bernoulli’s principle states that as the velocity of a fluid decreases the pressure exerted by the fluid increases
True of Flase
The power that a hydraulic system must develop is dependent upon the job that the system is trying to accomplish
True
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 output power
Output power (kW) = flow rate(L/min) x pressure (MPa) x 0.0167(constant)
Describe hydraulic system inefficiency
A system that does not effectively transmit power is said to be inefficient
How is hydraulic system efficiency determined?
Hydraulic system efficiency is determined by comparing output power of a system with the amount of power required to drive the system(input power)
Power loss takes two forms what are they?
Pressure loss and flow loss
True or false
There must be a difference in potential energy in order for flow to occur in a hydraulic system
True
Potential energy that is lost is not destroyed but changed into what type of energy?
Heat energy
The greater the pressure lost in the system, the more _____ will be generated
Heat
Describe laminar flow
Oil should move through the system in straight parallel flow paths
Conductors of adequate size with smooth transition in cross-section and hl Direction will provide lower fluid velocity and turbulence which results in lower pressure losses and he generation
