Vane compressor Flashcards
What is pressure ratio?
Ratio of the absolute incoming air pressure to the absolute
compressor discharge pressure.
What is the casing?
Metal outside structure that holds all the components in place.
What is a stator?
Stationary inner metal cylinder that the vanes contact and slide
across as they turn within the unit. Machined as a separate unit and
contains inlet & outlet ports, oil relief valves and oil release valves..
What is a rotor?
Only rotating part in a vane compressor.
What is the purpose of the bearing carriers?
Locate the rotor in the correct position
What are vanes?
Metal or composite sliding parts that fit into rotating block slots
What purpose do the bearings serve?
Support and position the rotor in the off centre position within
the stator ring so no metal to metal contact takes place.
What types of valves are found on vane compressors?
Min. pressure valve, check valves, unloader valves, servo
valves, oil relief, oil return, oil release, safety relief and vacuum
What is the purpose of the minimum pressure valve and where
is it found?
Allows the wet sliding vane compressor to build enough
pressure to get oil lubrication system working 1st before sending any
air out into they system. Located at compressor discharge.
What is the purpose of the check valve and where is it found?
Prevent back flow of compressed air into the compressor on
shutdown. Located at discharge. On wet vane it is located in the
minimum pressure valve assembly, plus another in the unloader
valve to prevent compressor air and oil mixture from discharging
though the inlet on shutdown.
What is the purpose of the unloader valve and where is it
found?
Regulates incoming air and matches it to the system
requirements. Found after the inlet are filter but before the rotor.
What is the purpose of the servo valve and where is it found?
When opened, allows oil pressure to reach the unloader valve
and move it to the closed position. Found in the oil reservoir just
before the unloader valve.
What is the purpose of the oil relief valve and where is it found?
Allows trapped oil an escape route to prevent hydraulic lock.
Found on Stator near the compressor discharge.
What is the purpose of the oil return valve and where is it
found?
Allows separated oil, but not air, to be fed back into the
compressor intake.
What is the purpose of the oil release valve and where is it
found?
Allows oil to drain back into the reservoir to prevent hydraulic
lock. Found on bottom of the stator.
What is the purpose of the safety relief valve and where is it
found?
Prevents over pressure of the casing and to unload the
compressor for ease of starting. Found on the casing between the
rotor and minimum pressure valve.
What is the purpose of vacuum valve and where is it found?
Used to break the vacuum that causes blade instability, found
near the compressor intake.
What are internal valve ports and where are they found?
Allow air into the inlet or out of the outlet chamber at the correct
time during the cycle. Cast into the stator ring at specific locations.
Roughly how often should you change vane compressor oil and
grease?
10,000 hours and grease every 6 months
What is a common problem with the servo/unloader valve
modulation control?
Valves get stuck and blow relief valve.
In a sliding vane compressor, explain the position of the rotor,
which enables it to compress air.
Set in the stator off centre.
What type of compressor requires the vanes be made from a
special material with a low coefficient of friction such as teflon or
graphite?
Dry Vane
What type of compressor is flooded with oil all the time that it is
running?
Wet vane.
How do vane compressor systems often eliminate the need for
an air receiver?
By using an inlet throttling system
What is the only major moving part in a sliding vane
compressor?
Rotor Assembly.
What does it mean for a compressor to have a built in pressure
ratio?
The pressure ratio is not adjustable as are reciprocating
compressors.
- What prevent the high pressure discharge air from leakage
back into the low pressure suction area?
Centrifugal force along with an oil seal on the vanes.
How is compressor capacity determined on a vane
compressor?
By calculating the volume of air between the two sets of vanes
at maximum volume multiple by the number of vanes multiplied by
the rpm of the motor.
Why do non-lubricated vane designs generally produce air at
low pressures?
They cannot sustain high temperatures generated when high
pressures are required and they have increased friction from vanes
sliding on the cylinder surface.
What is the purpose of the oil in the wet vane compressors?
Cool, seal, lubricate, prevent corrosion and operate the servo
valve.
What is the principle involved with designing a vane
compressor system without and air receiver?
The air pressure being produced inside the casing is used to
control the position of the inlet unloader valve, which matches
compressor output to system requirements.
On a wet vane compressor, what part gets rid of the majority of
oil as soon as it passes through the discharge port on a stator?
The labyrinth seal.
Which valve on a wet vane serves the purpose of ensuring that
the oil circulation system is satisfied first, before the compressor
sends any air into the system?
The minimum pressure valve located on the pressure
discharge.
Under what condition does the minimum pressure valve open?
As long as system pressure is above 60psi
How is the reverse flow of air, along with condensed water
vapor and other contaminants prevented from entering the
compressor?
The check valve portion of the minimum pressure valve slams
shut or on larger compressors, there is a check valve in the
discharge line.
On the wet vane, which valve is normally open on startup and
which is normally closed?
The unloader is normally open and the servo is normally
closed.
Why must you have a good seal on the vanes while they rotate
and compress air?
As compression is occurring, each blade is at a slightly higher
pressure so the air is always trying to leak back towards the suction.
Within a wet vane compressor, why must you remove the oil
vapour while the air/oil mixture is still quite warm?
If the moisture in the air were allowed to cool too much, the
water vapour could condense and contaminate the oil.
Whats the purpose of an oil relief valve?
To prevent hydraulic lock or overpressure and breakage.
What stops the oil from going to the cooler and warms up up
quicker to get it to the proper temperature for proper lubrication?
Oil bypass valve.
Why does a safety relief valve need to be installed on the
casing of the wet vane compressor?
If the minimum pressure valve were to get blocked off, the
compressor could blow itself apart.
Which valve could cause high pressure air to leak into lower
pressure areas of the compressor causing the compressor to work
harder and trip the breaker?
Oil relief valves if they are not seating properly.
What happens if the inlet unloader is stuck in the closed
position?
No air can be pulled so no air can be delivered.
Vane compressors are
Positive displacement constant volume compressors with built in pressure ratio
