Third Year Millwright Hydraulics Flashcards
Flow control valves control:
speed
Pressure Control valves control:
force
Flow control valves can be either:
compensated or non-compensated
Flow control valves can be used for:
metering
Needle Valves include a:
fixed orifice
Compensated control valves:
adjust for pressure and temperature changes
When fluid gets hot it becomes less viscous, therfore it may be best to use a:
Compensated needle valve
A hydraulic vane motor without springs would never
get started, the springs are necessary to hold out the vanes against the stator.
If the veins are non metallic, the vane compressor does not need
oil in the stator (dry compressor)
of vanes x max volume between vanes x number of vanes =
Maximum Displacement
Increasing RPM on a Vane Compressor
Increases Output
In a vacuum pump situation, the discharge is:
exhaust
Liquid Ring compressors offer:
cool, clean, pulse free air with little vibration
Are reservoirs obligatory on Rotary Compressors:
No, they run for extended periods of time and can provide output when needed downstream
The minimum pressure valve sends a signal to the compressor to:
start up
The more open the inlet valve, the more:
volume is delivered
The butterfly valve is involved in:
modulation control
The oil bypass valve senses oil is:
cold, so it keeps it in the sump until it warms up from discharge pressure
The safety relief valve is used when:
there is a stuck minimum pressure valve or blocked labyrinth passages
Bearing Carriers:
Locate the rotor(s) in the correct position
Holes drilled in Vanes decrease:
the weight
When the compressor is not running, the oil level in the separator is:
high
Vane compressors can overheat from:
running too much
metering in can cause
cavitation
If a meter valve is placed before the directional valve then:
both directions are metered
meter in and meter out do not control
pressure, they only control flow
pumps can produce flow, but not
pressure
in a stack valve the pressure relief valve should be placed closest to the
subplate
System for stack valves:
ISO
If a stack valve needs to be able to handle higher pressure, a higher:
flow capability is needed
cartridge valve advantage:
are less expensive
Screw in Cartridge valves are good for:
30-35 GPM
Slip in type cartridge valves:
slip into standardized cavities in manifold block
Proportional Valves get their name because:
spool can be infinitely positioned, proportional.
Coil current proportional valves:
moderately precise
Dead Band
distance armature moves before spool functions
Gain formulae is
output volts divided by input volts
A subplate is located where stacking valves meet:
hydraulic lines, or conductors
An amp card controls:
electrical input to the solenoid
Dither is a:
high frequency AC signal superimposed onto the valves DC signal
DC current gives more torque and it is
easier to use
DC signal tells us where the valve:
is (it’s position in a proportional valve)
Histerisis definition
dependency of a condition on the previous condition
Ramp Functions
increase or decrease voltage to the solenoid, this way we can eliminate shocks from fast stops and starts.
Non feed back control:
used for smooth control of actuator speed.
Non feed back control offers:
moderate accuracy
Internal feed back senses where the:
Directional Control Valve is
Closed outer loop reads where the:
actuator is
Closed inner loop tells us:
where the spool is
Open loop
non feedback
A type of proportional relief valve that uses a simple spindle to close the opening of a small nozzle:
Nozzle Type
A nozzle type relief valve is set by:
electronic pressure, not hydraulic
When the armature is pulled in on a nozzle type relief valve, the spindle moves in and allows:
oil to return to tank when over pressure limit
plate type
when hydraulic force overcomes electrical force the oil will flow
poppet type LVDT
proportional spool type valves have bleed screws
servo valve
has a feedback wire for torque motor
Mechanical servo valves
essentially a force multiplier
Flapper nozzle type
two stage, infinite positioning, servo spool for dead band
Jet pipe Type
Pressure at each end of the valve spool, signal to torque motor changes jet pipre and more fluid flows to one side than the other.
single stage servo valve
direct, moves spool one way or the other
Filtration and servo valves
located in valve and before the valve
pumps convert
mechanical energy into hydraulic energy
To have a positive flow to pumps at all times:
they must not suck air
reservoirs are pressurized on mobile equipment for two reasons:
to keep dirt out, and so pump does not need to suck air
hydrodynamic pumps
non positive seal, primarily for fluid transfer
on a positive displacement pump, if it is shut off:
no fluid flows from discharge to suction
Positive Displacement Pumps are unloaded by:
pressure relief valves
Closing the inlet port will cause:
cavitation and ruin the pump
Positive displacement pumps work on a
pressure differential
Pump efficiency
(GPM delivered divided by theoretical GPM capacity) X 100
Pressure Gauges require
calibration
pump efficiency decreases as
pressure increases, due to slippage
volumetric efficiency of the pump is affected by:
pressure
Vane Pumps are rated at what RPM?
1200rpm
If we keep the pump RPM at the engineered spec then we know pump:
displacement is correct
four types of piston pumps:
in-line, bent axis, rotary, radial
oil holes in a piston pump allow oil to flow to the:
low pressure side and prevent metal to metal contact, this is why a case drain is necessary
All piston pumps have a:
squash plate
If there is a hump on the pump casting then the:
squash plate can be moved
If the flow remains constant but we change the swash plate angle it changes the:
displacement
High Pressure on secondary piston (yoke) moves the:
swash plate
30 degrees from perpindicular is the swash plates
maximum displacement
