Pneumatics Flashcards
Name three types of compressors.
Reciprocating
Screw
Vane Rotary Lobe
Centrifugal
There are two main categories of air compressors; what are they?
Positive displacement
Dynamic
What is the main advantage that multi-stage compressors have over single stage compressors?
Ability to achieve higher pressures through less heat build-up at high pressures which results in greater efficiency.
Name two key characteristics of all good compressor lubricants.
Resist Oxidation
Protect against corrosion
Good lubricity
Low carbon-forming tendencies
In an oil-flooded rotary screw compressor, what functions does the lubricant perform? Name 3.
Seals
Cools
Lubricates
How do compressors generate water? How do you get rid of it?
Humidity from the air condenses under pressure. It is removed in the coalescer or knock out drum. Also should be drained from aftercooler
and intercooler.
Why is a dryer or a knockout drum needed in a pneumatic system?
It removes contaminants and condensed water
What is the difference between a double-acting and a single-acting reciprocating compressor?
Double acting compressors have compression on the return stroke.
How is volume and pressure controlled in an axial piston?
By adjusting the angle of the swashplate.
What is a swashplate?
A component of a piston pump that rotates and causes pistons to move back and forth inside a piston bore.
What happens to the temperature of gas as it is compressed?
It increases
What should all compressors have on intake?
A Filter
What is an FRL?
Filter Regulator Lubricator for an airline oiler
What three advantages do rotary vane and rotary screw compressors have over reciprocating compressors?
Quieter
More compact and cheaper to operate
Uniform (non-cyclic) discharge pressures
What removes heat generated during compression?
Intercoolers (and the lubricant)
What could be the cause of fire and explosion in a compressed air line?
Carbon can build up on discharge valves allowing them to stick open. This causes hot air to get sucked back into the compression chamber where it is recompressed. The air can generate enough heat to ignite the deposits and cause fire or explosion.
Name the sequence of events in the compression cycle of a reciprocation air compressor, starting with the piston moving down the cylinder.
Piston moves down, volume increases, inlet valve open, air is drawn into cylinder through inlet valve. Piston reaches bottom of stroke. Inlet valve closes, discharge valve opens. Piston returns, volume decreases, air is compressed. Air is expelled out of the discharge valve. Discharge valve closes. Piston reaches the top of stroke.
_______________ act as reservoirs for compressed air.
Receivers
What are some important factors to consider when choosing a lubricant for a reciprocation compressor?
Good oxidation stability
Low deposit formation
Correct viscosity
Compatibility with the gas that is being compressed
Why is a dryer or knock out drum needed in a pneumatic system?
The air either must be dried prior to compression or a knock out drum installed downstream of the after cooler to prevent condensation. The elimination of moisture is particularly critical when instrument air for pneumatic controls are involved. Moisture removal is also important for pneumatic tools. Wet air promotes rusting and tends to remove oil from lubricated surfaces in contact with air.
What does positive displacement mean?
Increase in pressure by reduced volume
Pump output is constant regardless of pressure
