hydraulic principles Flashcards
advantages of hydraulic systems are
compact . light weight . powerful . can occupy a small space . more flexible than mechanical . cooling and lubricating easy to accommodate . operator can control several functions at one time . smooth and protected from overload without engine stall
disadvantages of hydraulics
fluids under pressure . noise . oil leakege can cause fire or contamination . temp variations can affect performance air pockets can cause spongey operation
what is work
work is force acting through a distance
in order for a hydraulic system to do work it must generate what
force . is the push or pull that is capable of producing or changing the motion of a body
what id energy defined as
energy is the ability to perform work
what are some forms of energy
mechanical. hydraulic. heat . electrical . chemical . light sound
some forms of wasted energy in a hydraulic system are
noise and heat
energy wasted in the form of heat can be caused by
internal leakage and the pressure required to push the oil through the system
what two states dose energy exist in
kinetic and potential
what is kinetic energy
is responsible for movement and motion
in a hydraulic system kinetic energy is created by what
the flow of oil through the system . the greater the rate of flow the greater the speed of the implement
what is potential energy
is the energy stored in a body or a substance
if given the opportunity potential energy will change its state to what
kinetic energy and work will be accomplished
what is an example of potential energy in a hydraulic system
an accumulator
in bernoullis principle as velocity of a fluid decreases
pressure exerted by that fluid increases
what dose flow rate determine
the speed of a cylinders movement .ie the time required to raise the load
formula for output power (Kw)
flowrate (L/min) x pressure (Mpa) x 0.0167
how is hydraulic system efficiency determined
by comparing the output power of a system with the amount of power required to drive the system ( input power )
what are the two forms of power loss
pressure loss and flow loss
what must there be in order for flow to occur in a hydraulic system
difference in potential energy
what is laminar flow
oil that moves through a system in straight parallel flow paths
conductors of adequate size with smooth transitions in cross section and direction will provide
lower fluid velocity and turbulence resulting in lower pressure losses and heat generation
turbulence can be caused by
conductors that are to small . abrubt changes in cross section . abrupt changes in direction
increased friction from turbulence will cause
increased power loss to heat generation
what is backpressure
pressure created by resistance to flow on the return side of a system
what will excessive back pressure cause
will increase the internal resistance of a system and cause reduced system efficiency
why are most hydraulic components designed with small amounts of internal leakage
for lubrication of moving parts . seals and supports
series hydraulic circuit
offer only one path for oil to flow ( lower torque but higher speed )
parallel hydraulic circuits
divides the oil flow between components ( higher torque but lower speed )
series parallel hydraulic circuits
can be both series or parallel and uses a pilot operated two position control valve
hydraulic systems are expected to
transmit increased power . operate at higher pressure . operate with greater efficiency . perform at higher speeds . operate with greater control
three general categories of hydraulic oil
petroleum based . fire resistant . biodegraeable
most commonly used hydraulic oil
petroleum based
selecting correct viscosity for system requirements and climactic conditions is essential to
prevent wear . seal internal parts
viscosity index is a term that refers to an oils ability to
resist changes in viscosity as temperature rises and falls
the lower the VI number of an oil
the greater its viscosity will change with temperature variations
what is viscosity
an oils resistance to flow
what do anti wear additives do
develop a protective film on moving parts
what has a significant effect on oil oxidization
oil temperature . the higher the temp the higher the rate of oxidization
as oil oxidization becomes more severe
smells burnt . leaves varnish and sludge on components . dark in color
oil that has been severely oxidized will feel
slippery and will not adhere to your fingers
all hydraulic oil will contain
some water
oil with a 0.5% water in emulsion will appear
dull or smoky
oil with a 1% water in emulsion will appear
milky
water-oil emulsions consist of a mixture of
60% water 40% oil
Invert emulsions consist of a mixture of
60% oil 40% water
water glycol fluids consist of
60% glycol 40% water with a chemical thickener added
water based hydraulic fluids cannot be operated at a temperature higher than
60 C or 140 F because the water will evaporate causing fluid viscosity change
synthetic fire resistant fluid
chemically remanufactured . most common type is phosphate ester
disadvantages to synthetic oil
expensive . not compatible with nitrile rubber seals must be replaced with viton seals
what two conditions must biodegradable fluids meet
70-80% of base fluid must be able to be broken down . non toxic
when selecting a proper hydraulic fluid you should
consult manufacture . take ambient temps into consideration . fluid is compatible
what is one of the main contributors to hydraulic component life
contamination
four common places for ingressed contamination
air breather. pump inlet . cylinder seals. unclean maintenance
three types of contamination failures are
catastrophic . intermittent . degradation
catastrophic failure is
rapid or sudden total disabling of a system or component
intermittent failure is
problem moves from component to component called transient failure > hard to TS
degradation failure
caused by gradual surface wear . will lead to catastrophic if left un delt with
