A It is equipment to inject the lubricant oil in to the air line , or the air tools.
Normally it was combined with the filter regulator.

A Yes , ISO VG32 or same standard .

A 1. Used for the single machine :



2.Used with the air tools :


3. Used in the whole air line .

A

A Air Regulator we also called air prressure reducer :
For example : If the air source pressure is 1.0Mpa , through the air regulator we could keep the outputing pressure at a Specific valve, even there is air consumption.
But the cheater valve is similar a follow control valve , if there is no air consumption , the pressure of the both side of the chearter valve will be same . 
Cheater Valve:
 

A How many types of the air regulator? 
There are three kinds of classification by the adjusting pressure :
High Pressure :3.5Mpa-30Mpa
Middle Pressure :0.5Mpa-3.5Mpa
Low Pressure:0-0.4Mpa
By the place where the air regulators were use , there are also three types :
1.Were used together with with small air pump Such as :
http://www.neu-master.com/ARC-Series-Air-Compressor-Filter-Regulator-pd6272180.html
2.Used as the whole airline regulator :http://www.neu-master.com/QTY-Series-Air-Regulator-pd6930963.html
3.Installed on the single machine to control the input air pressure:http://www.neu-master.com/R-Series-Air-Regulator-pd6775963.html

A Where the air regulator was used ?
With the small air pump whcih were most used in the house.
With the machine that need be actuated by pressured air .
With the Center Air Pump to ajust the output pressure for the whole air using system .Normally is the high pressure air regulator .

A The air regulator , were also called air pressure regulator .
It was used for adjust the output air pressure .
For example the input air pressure is 140 Psi , normally we could adjust the output pressure from 0 to 140Psi in the situation that there is no rate of flow .
When there is flow from the output side ,the pressure that showed by the pressure gauge  may a little lower than we fixed .It is the normal situation .
 

A

What Does FRL mean? 

Answer:

F. is the abbreviation of air pressure filter, which are used in the pressured air line, to filter the dust, water etc from the high pressure air .

R. is the abbreviation of air pressure regulator. Which to adjust the output air pressure . For example : the input air pressure is 0.8Mpa , and you want the output pressure 0.4Mpa , then we must use it .

L. is the abbreviation of air pressure lubricator, it supply the lubricating oil for the downstream equipment,

such as cylinders ....

So frl mean the air filter+regulator+lubricator.