Compressors - Fundementals

Question 0

Name 3 ways air pressure can be increased?

Answer 0

reduce the volume (the space the molecules are in)
heat the gas
pack more gas into a confined space

Question 1

What are the 2 main differences from compressed air and oil in a hydraulics system?

Answer 1

gas can be compressed and gas expands to fill any container

Question 2

How do compressors move gases and do work?

Answer 2

By raising the gas pressure

Question 3

On what principle do positive displacement compressors work?

Answer 3

They trap a specific volume of air and then reduce that volume (compressing) to get a higher pressure

Question 4

Define Bernouli’s Principle?

Answer 4

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.

Question 5

Define Pascal’s Law?

Answer 5

The pressure applied to a confined fluid is transmitted equally in all directions while being transmitted at right angles to the surface.

Question 6

Name 3 non-positive displacement (Dynamic) compressors?

Answer 6

Axial Flow, Centrifugal, Ejector

Question 7

Name the 2 types of positive displacement compressors and examples of each?

Answer 7

Reciprocating -Single Acting, Double Acting

Rotary - Sliding Vane, Liquid Ring, Screw (Single rotor, Two rotor)

Question 8

What are the 2 types of flow and explain what each are?

Answer 8

Laminar - Flow in a straight line

Turbulent - Flow with sharp bends which causes friction and resistance.

Question 9

Name 2 types of reciprocating compressors suited to oil-free delivery and why?

Answer 9

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.

Question 10

What is an integral compressor?

Answer 10

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

Question 11

What causes the reciprocating compressor valves to open?

Answer 11

Pressure differential between the inside of the cylinder and the outside of the cylinder in the suction or discharge passages.

Question 12

List 3 components that the ABSA requires to be installed on any air receiver?

Answer 12

Safety relief valve
pressure gauge
drain

Question 13

What must be installed on the pressure side if there might be a blockage?

Answer 13

Safety relief valve

Question 14

How does altitude affect a compressor?

Answer 14

reduces efficiency because the air is thinner making less be compressed in the same amount of time.

Question 15

What is the purpose of the crosshead and guides?

Answer 15

to keep the piston rod centred through the packing.

Question 16

What is a Distance Piece?

Answer 16

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.

Question 17

What do you need to be careful of when setting the safety relief valve?

Answer 17

It can not be set higher than the lowest maximum pressure rating of any part of the system.

Question 18

How does compressor unloading happen and list some methods?

Answer 18

Unloading controls the pressures the compressor is supposed to maintain. It can be done though start/stop, inlet valve unloading & variable speed.

Question 19

How does cooler air affect a compressor?

Answer 19

It makes the compressor more efficient and does not allow for as much moisture.

Question 20

Why would you add stages to a compressor?

Answer 20

To add volume without overheating

Question 21

What is Clearance Volume?

Answer 21

the space between the piston and the cylinder head when the piston is at TDC.

Question 22

What are Clearance Pockets?

Answer 22

they increase the clearance volume to reduce capacity of a cylinder.

Question 23

What is Rod Loading?

Answer 23

The sum of the suction and discharge pressures acting on both sides of a double-acting piston.

Question 24

What is Rod Reversal?

Answer 24

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.

Question 25

What is the difference between Purging and Venting?

Answer 25

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.

Question 26

What type of compressors use bernoulli’s principle and how?

Answer 26

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

Question 27

What does Rod Runout mean and what are some of the causes?

Answer 27

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

Question 28

What two things need to be in absolutes?

Answer 28

Temperature because there all molecular action in a gas stops and pressure because it’s zero at absolute zero

Question 29

How does temperature effect pressure?

Answer 29

If air is hotter it becomes thinner and will make it more difficult for the compressor to create pressure

Question 30

What is a barometer?

Answer 30

Measures vacuum and pressure. It’s made of a tube filled with mercury and inverted into a pool of mercury

Question 31

What is a manometer?

Answer 31

Most accurate way to measure vacuum. A specially shaped u tube filled with a specific oil or water

Question 32

What is a bourdon tube?

Answer 32

A specially shaped hollow curved tube made of brass which straightens out to measures pressure

Question 33

What are water traps?

Answer 33

They trap and remove water in a compressed air system.

Question 34

When calculating Combined gas law calculations what do you need to remember?

Answer 34

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.

Question 35

Where will you find the FRL?

Answer 35

After compression and before use.

Question 36

Why does the coolant need to be a little higher in temperature than the gas?

Answer 36

To prevent condensation from building inside the cylinder

Question 37

What are 2 ways the piston is connected to the rod?

Answer 37

Against a shoulder and a nut or on a taper with a locknut

Question 38

What do receivers do?

Answer 38

Store energy and dampen pulsation.

Question 39

What is a VVCP?

Answer 39

A variable volume clearance pocket. It has an adjustable piston that changes the size of the clearance pockets.

Question 40

What is the unloaders most often used on oil and gas compressors?

Answer 40

Suction valve unloaders and bypass unloaders.

Question 41

What is to rule for setting piston to head clearance?

Answer 41

Set the crank head clearance at 1/3 and the head end clearance at 2/3 of the total

Question 42

What can be done to ensure the main frame and distance piece is not supporting all the weight of the cylinder?

Answer 42

The cylinder support can be preloaded to take some of the weight.

Question 43

Piston secured to piston rod?

Answer 43

Pressure fit?

Question 44

Direction lubrication goes

Answer 44

Closest to piston

Question 45

Vacuum

Answer 45

• occurs when the pressure in a container is less than the pressure surrounding it.
• max force in a perfect vacuum is 14.7 pounds

Question 46

Increase in altitude

Answer 46

-causes a decrease in atmospheric pressure