Rotary compressors Screw, vane, dynamic liquid ring Flashcards
rotary screw compressors are positive displacement compressors designend to deliver_____________ with a specific built in ___________
varying volume, pressure ratio
constant volume, pressure drop
constant volume, pressure ratio
varying volume, safety valve
Constant Volume, Pressure ratio
if you saw a screw compressor apart, how would you know it was a dry screw compressor
it would have no oil lubrication entering the screw
it would have extra sealing between the screws and bearings
it would have timing gears
all the above
All of the above
the location of the discharge port determines the pressure ratio of the screw compressor
true
false
True
leakage in the screw compressor can happen ____________ and can be partly eliminated by _____________
between stages, decreasing the rpm
between the rotors, increasing the rpm
between the rotor and housing, injecting oil
both the 2nd and 3 option are correct
Both second and third options are correct
if you wanted to produce a high pressure and low volume out of the screw compressor you would use a ___________________
4+6
3+4
6+8
they all would work
6+8
6.a single screw compressor has 1 main rotor and 2 star rotors on opposite sides
true
false
True
The fixed bearing in a screw compressor must be located at the intake end of the compressor
true
false
False
Must be installed at the outtake end to maintain the proper clearance of the screw and the end plate
oil flooded screw compressors use oil to cool the compressed air and ___________between the rotors
wash
seal
purge
vent
Seal
proper maintenance of the screw intake air filter will help
improve the efficiency of the compressor
extend the temperature range the compressor can operate at
decrease the pressure drop across the filter
all the above
Improve the efficiency of the compressor
on a wet screw compressor the purpose of the minimum pressure valve is to help get the oil flowing in the lubrication system on start up bu building up pressure to 20 -50 psi
true
false
True
.the main purpose of the blow down valve is to vent the pressure from the separator on a shutdown, to prevent oil from beng pushed out the compressor inlet and inet filter
true
false
True
displacement control for a screw compressor can be done by
turn valves
poppet valves
slide valves
all the above
All of the above
variable capacity control can be achieved by moving slide valves and slide stop controls together or independently
true
false
True
when maintaining compressor separators, the gasket must have the staples left in to prevent over-pressuring the sump
true
false
False.
Staples are to ground and reduce risk of explosion
for every 18 degrees F in crease in mineral oil temperature above 135 degrees F, the oxidation rate doubles.
true
false
true
if your screw compressor has low air delivery, it could mean that
the inlet is restricted
the blowdown valve is stuck
the air / oil separator is plugged
all the above
All of the above
2 and 3 lobe blowers are considered to be ______________ volume , _______________ pressure machines
low, high
high, high
high, low
low, low
High. Low
2 and 3 lobe blowers _____________ (inside the casing)
compress air
do not compress air
Do not compress air
lobe blowers must have _________________ to maintain the clearances inside the unit
oil
seals
pressure differential
timing gears
Timing Gears
any leakage from the discharge back to the inlet on a blower is known as
negative flow
effciency
slip
positive flow
Slip
the 3 lobe blower has a higher efficiency that 2 lobe blowers
true
false
True
helical lobe blowers
compress air in side the housing
create operating pressure of 20 - 50 psi
have an unequal number of lobes on the 2 rotors (2+4)
all the above
All of the above
timing gears should be of a high quality and have excessive backlash in the gears to keep the rotors in proper mesh
true
false
False
oil seals on blowers are usually labyrinth with some type of lip seal
true
false
True
when maintaining lobe blowers, you should always turn it over by hand to make sure it rotates freeely and than bump start motor to find the correct ________________ before running the system
clearances
mate marks
rotation
position
Rotation
when checking clearances, it is important to rotate the impellers thru 360 degrees and obtain at least the minimum specified clearance
true
false
True
impeller to impeller cleanance on lobe blowers is usully taken at a ____________ degree position
25
35
45
90
45
A 16.38 lobe blower size – tells us it has a
16” length rotor, 38”, timing gear
16” diameter timing gear, 38” length rotor
this number does not tell us anything about a blower
16” timing gear driving a 38” timing gear
16” diameter timing gear, 38” length rotor
if a knocking sound is heard inside the blower, it may mean the unit _____________
has to much oil in the gear housing
is out of time
has excessive rotor clearances
has worn shaft seals
Out of time
vane compressors work on the principle of an inceasing area on the intake cycle and a decreasing area on the compression cycle.
true
false
True
if the vane compressor is oil free, you would need to use
vanes made of cast steel
vanes made of teflon compounds
vanes made of graphite compounds
both the 2nd and 3rd answers are correct
Both second and third answers are correct
there is an extra cut in the stator of the vane compressor, that matches the rotor diameter. this is to help
increase the clearances between rotor and stator
decrease clearances between rotor and stator
increase the sealing area between rotor and stator
increase clearances and increase the volume of the trapped air between the vanes
increase the sealing area between rotor and stator
in the minimum pressure valve / non-return valve, the check valve helps prevent reverse flow of the air flow.
true
false
True
automatic air control is accomplished by the use of the unloading valve and the ______________
pressure relief valve
servo valve
oil return valve
sump valve
Servo valve
oil relief valves are used to help stop ______________
moisture build up
oil hydraulic lock
high air pressure
none of the above
oil hydraulic lock
when overhauling sliding vane compressors, careful attention should be paid to
positioning of the shims
new vane end clearances
O-ring seating
all the above
All if the above
when match marking the end cover to stator, do NOT use ________________ as this will damage the sealing serfaces
hammer and punch
etching tool
felt pen
both the 1st and 2nd answer is correct
Both 1st and second answers are correct
multi-stage centrifugal compressors increase the volume and overall pressure ratio to achieve higher discharge pressures
true
false
True
casing styles for centrifugal compressors are sectional, horizontal split and vertical split. the one that is used for high pressure is
sectional
horizontal split
vertical split ( barrel casing)
all can be used for high pressure
Vertical split (barrel casing)
impellers can be of the open, semi-open, and closed design. the design that is used for rough service environments is the
open
semi-open
closed
all can be used for rough service environments
Open
guide elements (stationary or adjustable diffusers) direct gas flow from one stage to the next in a multi-stage centrifugal compressor
true
false
True
labryrinth seals are installed on the diaphragm assembly in axial flow compressors to minimize internal leakage along the shaft between stages
true
false
True
thrust control on dynamic compressors can be accomplished by
balance pistons or drums
thrust bearings
impeller arrangements
all the above
All of the above
carbon seals are where there are low pressure differentials
true
false
True
a common axial thrust bearing is the tilting pad type
true
false
True
in an axial compressor, the rotors ____________ and the stators ________________-
increase the gas velocity, converts velocity to pressure
decrease the gas velocity, converts pressure into velocity
increases gas pressure, converts pressure to velocity
none of the above
Increase the gas velocity, converts velocity to pressure
an example of a rotor dixc blade mounting style is the fir tree
true
false
True
to correct blade fouling in axial compressors you can
add crushed walnut shells while still running
use special non-stick coatings
increase the RPM until material loosens
all the above
All of the above
the best operating range of all dynamic compressors is
at balancing points
between the surge point and the stonewall point
at the surge point
at the stonewall point
Between the surge wall and stone wall point
surge control is resolved by closing off the discharge valve and then redirecting some of the discharge air back to the inlet
true
false
True
the liquid ring compressor is an oil-free positive displacement pump that uses a ring of liquid to seal the spaces between the impeller vanes
true
false
True
air-flow into and out of the liquid ring compressor is thru a set of cones ( or port plates ) that surround the shaft
true
false
True
cooling of the compressed air in a liquid ring compressor is done by the
oil
cone
liquid ring
all the above
Liquid ring
when repacking a liquid ring compressor bearings with grease, you should pack the bearing full of grease and then fill the housing__________ with grease
1/2 full
full
1/4 to 1/3 full
to the bottom of the bottom rolling element
1/4 to 1/3 full
if you are repacking the packing gland, make sure you stagger the joints______ and mount the ____________in the proper position
45 degrees, end cap
90 degrees, end cap
45 degrees, lantern ring
90 degrees, lantern ring
90degrees , to the lantern ring
there are 2 main compressor classifications. they are
dynamic and axial
rotary and reciprocating
reciprocating and dynamic
non-positive and positive displacement
Non-positive and positive displacement
positive displacement works on the principle that
Option 1there is an increasing area and a decreasing area that lets in and compresses the air
air flows from low pressure to high pressure after the compressor
velocity increases in the volute and then pressure decreases in the lines
velocity increases thru the compressor and then slows down in the volute where pressure increases
There is an increase area and a decreasing area that lets in and compresses the gas
a dynamic compressor works on the principle that
the velocity is slowed down thru the compressor to create a pressure drop
the air velocity is sped up thru the compressor and slowed down in the volute to increase the pressure
the pistons create the pressure by allowing air flow into the intake and decreasing the pressure out the out feed
the pistons create the pressure with the stroke of compression
the air velocity is sped up thru the compressor and slowed down in the volute to increase the pressure
compressors are used for boosting pressure and gas gathering in the oil and gas industry
true
false
True
compressor unloading can be
start/stop
variable speed
inlet unloading
all the above
All of the above
heat always travels from hot to cold
true
false
True
