CHAPTER 27 Air Compressors Book 2

Question 1

Two types of air compressors

Answer 1

Positive displacement, and dynamic

Question 2

Difference in positive displacement and dynamic air compressor

Answer 2

Positive displacement, compressors, dry and a charge of free air traps it and reduces its volume then discharges it they are either reciprocating a rotary type dynamic compressor, accelerates air using impellers they convert kinetic energy of high velocity, low pressure into potential energy of low velocity, high pressure they are either centrifugal or axial flow.

Question 3

Volume versus pressure for air compressors

Answer 3

Positive displacement, compressors favor, pressure will dynamic favor, volume a reciprocating. It produces the most efficient pressure but the lowest volume were an actual unit produces high-volume but it’s not efficient and developing pressure.

Question 4

Single versus double acting reciprocating compressor

Answer 4

Set an acting compressor, compresses and discharges at one end of the cylinder only where a double action compressor presses and discharge takes place at both ends of the cylinder. Therefore, there are two compression strokes per revolution of the crankshaft.

Question 5

Sliding van compressor

Answer 5

The two compressor shafts are connected by a flexible coupling and the dry for the unit may be applied at either the high or low pressure side when this is set up as a two-stage compressor discharge pressure may be as high as 145 psi lubrication is provided by a belt driven lubricator it is less efficient than the reciprocating compressor but it has a lower initial caution produces a steady flow of air. It does not require discharge or inlet valves.

Question 6

Rotary lobe compressor

Answer 6

One impeller is driven directly in the other by means of timing gears. The impellers are to figure 8 shaped impellers, revolving in opposite directions. Lubrication is not required so the unit is turmoil. Free pressure produce are quite low boat 14 psi for a single stage and 29 two-stage big advantage is it produces even flow of oil, free air

Question 7

Rotary screw compressor

Answer 7

Male rotor has for convex lobes the female rotor has six concave flutes. The rotor is generally driven on the Mehl side with the female being driven by means of a driving time in gear. If the male rotor makes contact it needs to be lubricated. If not, it can be lubrication free advantages are compactness, vibration, free operation, smooth flow, and requires no suction or discharge vowels the eficiency is less than a reciprocating tape

Question 8

Centrifugal compressor

Answer 8

Uses impeller to draw air in the air, passes through a volute shaped casing where it converts velocity to pressure. They also use a stationary ring, fuse or veins in addition to the casing to create the pressure can be set up as a multi stage compressor having several several impellers, on one shaft commonly used for large volume, low pressure applications they do not require lubrication cells they supply oil, free air. Near efficiency is lower than positive displacement type increasing gears are used as the impellers need to spend the very fast

Question 9

Intercoolers

Answer 9

Can be either air, cooled or water cooled when air cooled consists of a filled pipe through which the compressed air passes when water cooled is it shell and tube construction main use is to remove water vapor and oil vapor from the air between the compressor in stages by condensing the air or oil also cooling the air increases the efficiency of operation reduces power consumption by around 15%

Question 10

After cooler

Answer 10

This cools, the air after the compression is completed once the air discharges from the aftercooler, it passes through a cyclones separator where moisture and other particles are removed from the air

Question 11

Variable speed control for a air compressor

Answer 11

Used when the compressor is driven by a steam, turbine or an internal combustion engine to maintain the system pressure, constant value. The compressor speed is increase or decrease by regulating the steam or fuel supply to the combustion engine.

Question 12

The pilot type of air compressor unloader they operate in all except one of the following way

Answer 12

May open a bypass valve in the intake back to the compressor discharge

Question 13

Rotary lobe compressor runs at a speed up to

Answer 13

1750 RPM

Question 14

A piston rod and double acting compressor has

Answer 14

 linear travel at both ends

Question 15

Rotary screw compressor is suitable for speeds up to

Answer 15

12,000 RPM