Pneumatic Systems Flashcards
What are the two (2) main categories of screw compressors?
- oil-flooded (wet)
- oil-free (dry)
They may be either single-stage or multi-stage, depending on requirements
Which rotor is the driver on a screw compressor?
The male rotor is usually the rotor that is directly driven.
What determines the capacity of a screw compressor?
Rotor length, diameter, lobe/flute design and speed determine compressor capacity.
What determines the discharge pressure of a screw compressor?
The discharge pressure is determined by the location of the inlet port along the length of the rotor, the length of path along the lobes and flutes and the location of the discharge port.
What function does the oil in an oil-flooded screw compressor serve?
Dissipate some of the heat due to compression, seal the gaps between the rotors and the casing to prevent leakage, lubricate the bearings and gearbox and reduce the noise level.
Which is the simplest type of control system for screw compressors?
The simplest control system is online/off-line control.
Which control system allows the compressor to produce only the amount of air required by the system?
modulation control
What must be included to prevent rotor contact in a dry screw compressor?
Timing gears must be used to prevent rotor contact in dry screw compressors.
Where are the thrust bearings located on the screw compressor?
The thrust bearings are located at the discharge end.
Air filters should be able to remove particles down to what size before the air the compressor?
5 microns
What two (2) functions do oil separators perform?
- Separate oil from the air
- Act as an oil reservoir and act as an air receiver.
What two (2) functions does the minimum pressure valve perform?
- Maintains a minimum air pressure in the separator
- Acts as a check valve, preventing flow reversal
What is the function of the thermal mixing valve?
to maintain a minimum oil injection temperature.
What should be done first before putting a compressor back into service after an overhaul or motor change?
Check for correct rotation after motor or air unit replacement.
What is the advantage of the helical lobe blower over the two lobe blower?
increased pressure and smoother air delivery
What types of bearings are found on lobe blowers?
Single row ball bearings, double row ball bearings, deep groove ball bearing, spherical roller, cylindrical roller and angular contact bearings can be found on lobe blowers.
What should be determined before resetting the timing on a lobe blower?
Before attempting to retime and set lobe clearance, determine whether the unit is unidirectional or bi-directional rotation and always refer to the manufacturer’s operation/maintenance specifications.
What should be done before starting a blower after an overhaul?
Turn it over by hand to ensure that it rotates freely in the direction of rotation.
Care should be taken to prevent what from happening while you are attempting to set the lobe clearance in a blower?
Take care to prevent injury to the fingers or hands caused by pinching from the gears.
The energy of compressed air in the lines can cause severe whiplash when one end of a hose is let free. This can be overcome with an __________
that stops flow through the line if excessive flow occurs.
Excess flow valve
What must you do to vertical cylinders before performing any work on or around them?
They must be let down or mechanically blocked to prevent movement
Piping should be sized to minimize __________ by being large enough with as few bends as possible.
pressure drop
The purpose of a _________
in a pneumatic system is to lower the dew point
so that it does not cause problems in the system.
dryer
Why should you use as few bends as possible in pneumatic systems?
To minimize pressure drop
What is the function of a dryer in a pneumatic system?
to lower the dew point
so that it does not cause problems in the system.
Where can a cyclone separator be used?
Anywhere in the system that moisture might fall out.
What is the function of air receivers?
They are used to store compressed air to take up fluctuations in demand and allow the system pressure to vary within reasonable limits.
The purpose of the
_______ is to bleed off
excess system pressure before it becomes too extreme.
safety relief valve
Why does it matter if there are leaks?
Leaks waste energy (from compression) which increases expenses while reducing the performance of air tools and equipment.
Most compressed air systems run for long distances. This allows the air to cool below its _____________ which causes moisture to fall out of the air stream.
dew point
Flow control valves control the volume and therefore the speed of the _____________
actuator
Pilot operation refers to valves that are operated with _______________.
air pressure
____________ piloted means the air pressure within the valve is used to perform the shifting function.
Internally
The 3/2 valve can be used if the air needs to be released when the valve is closed. A
typical application is the operation of a _________ acting cylinder.
single
A ____________ acting cylinder is a common application of a 4/2 valve.
double
The ___________ is used to automatically select the higher of two pressure sources to supply a pneumatic signal.
shuttle valve
One of the first items to check in a malfunctioning system is __________________
whether there is a supply of air at sufficient flow and pressure.
