Flashcards in Compressors - Fundementals Deck (47):
What are the 2 main differences from compressed air and oil in a hydraulics system?
gas can be compressed and gas expands to fill any container
Name 3 ways air pressure can be increased?
reduce the volume (the space the molecules are in)
heat the gas
pack more gas into a confined space
How do compressors move gases and do work?
By raising the gas pressure
On what principle do positive displacement compressors work?
They trap a specific volume of air and then reduce that volume (compressing) to get a higher pressure
Define Bernouli's Principle?
If the flow rate is constant, the sum of the kinetic energy (velocity) and the potential energy (pressure) at various points are constant. So if the velocity decreases the pressure must increase.
Define Pascal's Law?
The pressure applied to a confined fluid is transmitted equally in all directions while being transmitted at right angles to the surface.
Name 3 non-positive displacement (Dynamic) compressors?
Axial Flow, Centrifugal, Ejector
Name the 2 types of positive displacement compressors and examples of each?
Reciprocating -Single Acting, Double Acting
Rotary - Sliding Vane, Liquid Ring, Screw (Single rotor, Two rotor)
What are the 2 types of flow and explain what each are?
Laminar - Flow in a straight line
Turbulent - Flow with sharp bends which causes friction and resistance.
Name 2 types of reciprocating compressors suited to oil-free delivery and why?
Labyrinth because it causes a seal with series of grooves machined on the piston and cylinder wall and Diaphragm because its membrane creates the barrier between the lubricating oil and the compression area.
What is an integral compressor?
It is an engine and a compressor combined into one frame that share a crankshaft. The engine provides the driving power for the crankshaft, while the compressor pistons take that power to compress the gas
What causes the reciprocating compressor valves to open?
Pressure differential between the inside of the cylinder and the outside of the cylinder in the suction or discharge passages.
List 3 components that the ABSA requires to be installed on any air receiver?
Safety relief valve
What must be installed on the pressure side if there might be a blockage?
Safety relief valve
How does altitude affect a compressor?
reduces efficiency because the air is thinner making less be compressed in the same amount of time.
What is the purpose of the crosshead and guides?
to keep the piston rod centred through the packing.
What is a Distance Piece?
Its the piece between the cylinder and the main frame to prevent contamination between the cylinder gases and the oil from the crankcase. It holds the oil wiper packing on the one side and the compression packing on the cylinder side.
What do you need to be careful of when setting the safety relief valve?
It can not be set higher than the lowest maximum pressure rating of any part of the system.
How does compressor unloading happen and list some methods?
Unloading controls the pressures the compressor is supposed to maintain. It can be done though start/stop, inlet valve unloading & variable speed.
How does cooler air affect a compressor?
It makes the compressor more efficient and does not allow for as much moisture.
Why would you add stages to a compressor?
To add volume without overheating
What is Clearance Volume?
the space between the piston and the cylinder head when the piston is at TDC.
What are Clearance Pockets?
they increase the clearance volume to reduce capacity of a cylinder.
What is Rod Loading?
The sum of the suction and discharge pressures acting on both sides of a double-acting piston.
What is Rod Reversal?
The alternating compression and tension forces of a piston that creates the on needed to allow oil to flood around the crosshead pin and connecting rod.
What is the difference between Purging and Venting?
Venting is releasing the pressure that could be inside a system. Purging is when you run the compressor with another gas to remove another gas that could be dangerous.
What type of compressors use bernoulli's principle and how?
Dynamic compressors speed up the gas giving it kinetic energy of motion and then slow it down to create pressure. Like a vacuum at home
What does Rod Runout mean and what are some of the causes?
When the piston is not running totally straight through the packing. Some of the causes are a bent piston, worn crosshead, improperly shimmed crosshead and piston rod locknut not seated properly
What two things need to be in absolutes?
Temperature because there all molecular action in a gas stops and pressure because it's zero at absolute zero
How does temperature effect pressure?
If air is hotter it becomes thinner and will make it more difficult for the compressor to create pressure
What is a barometer?
Measures vacuum and pressure. It's made of a tube filled with mercury and inverted into a pool of mercury
What is a manometer?
Most accurate way to measure vacuum. A specially shaped u tube filled with a specific oil or water
What is a bourdon tube?
A specially shaped hollow curved tube made of brass which straightens out to measures pressure
What are water traps?
They trap and remove water in a compressed air system.
When calculating Combined gas law calculations what do you need to remember?
Question will probably be given to you in psig so you need to convert to psia by adding 14.7 and convert temperature to absolute. Temp has to be in K for C and R for F.
Where will you find the FRL?
After compression and before use.
Why does the coolant need to be a little higher in temperature than the gas?
To prevent condensation from building inside the cylinder
What are 2 ways the piston is connected to the rod?
Against a shoulder and a nut or on a taper with a locknut
What do receivers do?
Store energy and dampen pulsation.
What is a VVCP?
A variable volume clearance pocket. It has an adjustable piston that changes the size of the clearance pockets.
What is the unloaders most often used on oil and gas compressors?
Suction valve unloaders and bypass unloaders.
What is to rule for setting piston to head clearance?
Set the crank head clearance at 1/3 and the head end clearance at 2/3 of the total
What can be done to ensure the main frame and distance piece is not supporting all the weight of the cylinder?
The cylinder support can be preloaded to take some of the weight.
Piston secured to piston rod?
Direction lubrication goes
Closest to piston
-occurs when the pressure in a container is less than the pressure surrounding it.
-max force in a perfect vacuum is 14.7 pounds