Third Year Millwright Hydraulics Flashcards by Andy Johnson

Flow control valves control:

speed

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Pressure Control valves control:

force

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Flow control valves can be either:

compensated or non-compensated

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Flow control valves can be used for:

metering

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Needle Valves include a:

fixed orifice

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Compensated control valves:

adjust for pressure and temperature changes

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When fluid gets hot it becomes less viscous, therfore it may be best to use a:

Compensated needle valve

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A hydraulic vane motor without springs would never

get started, the springs are necessary to hold out the vanes against the stator.

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If the veins are non metallic, the vane compressor does not need

oil in the stator (dry compressor)

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of vanes x max volume between vanes x number of vanes =

Maximum Displacement

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Increasing RPM on a Vane Compressor

Increases Output

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In a vacuum pump situation, the discharge is:

exhaust

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Liquid Ring compressors offer:

cool, clean, pulse free air with little vibration

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Are reservoirs obligatory on Rotary Compressors:

No, they run for extended periods of time and can provide output when needed downstream

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The minimum pressure valve sends a signal to the compressor to:

start up

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The more open the inlet valve, the more:

volume is delivered

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The butterfly valve is involved in:

modulation control

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The oil bypass valve senses oil is:

cold, so it keeps it in the sump until it warms up from discharge pressure

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The safety relief valve is used when:

there is a stuck minimum pressure valve or blocked labyrinth passages

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Bearing Carriers:

Locate the rotor(s) in the correct position

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Holes drilled in Vanes decrease:

the weight

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When the compressor is not running, the oil level in the separator is:

high

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Vane compressors can overheat from:

running too much

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metering in can cause

cavitation

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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