The Complete Guide To Compressed Air

air compressors
(Last Updated On: August 26, 2020)

Compressed air is generated by electro-mechanical means. Usually an electric motor will use electricity to turn a shaft, a pulley (sheave) will turn a crank of some sort, pistons will move up and down, and larger volumes of free air in the cylinder piston get scrunched down into smaller sizes. How’s that for technical?

compressed air

If you jam enough air from the cylinders into a tank (receiver) then the pressure in that tank will start to rise. And it will continue to rise, until such time as the pressure inside that tank reaches a set point. For a DIY home compressor that’s usually in the 90-120 PSI range. An industrial compressor might have a higher set point, depending on the pressure that plant needs for their air consuming applications.

It’s what happens to the air as it’s compressed that I want to address here.

As your compressor jams air into the tank the space available between each molecule of air gets smaller. This forces those molecules of air to “rub” against each other more often, increasing friction. As we all know, friction creates heat.

So as your compressor compresses air into the tank the process generates heat. And there could be lots of heat generated, depending on how big the compressor is and how long it runs. Even if it’s a small DIY home compressor, after a while, you can feel that the tank is warmer as the air gets compressed into it.

So why care?

The issue with heat generation has a couple of ramifications.

One of those is that the compressing of air can generate enough heat to provide it to other applications or uses in the plant. There’s lots of information on the internet about using compressor generated heat. Here’s some information to get you started.

Another by product of heat in the compressed air is water.

The hotter the compressed air in the tank, the more water can be held by that air. When that water-laden air moves out into the air lines or air mains on it’s way to your application, that air cools. As the air cools, it’s ability to hold water lessens, and the water vapor condenses into free water in the air lines. Sometimes, depending on the size of the compressor and lines, that water generation can be measured in gallons!

It’s this water, the vapor that condenses in the air mains and air lines, that can wreak havoc on your compressed air equipment. Regardless of what you are doing with compressed air the odds are that water spraying out along with your air won’t be good for your valves, cylinders, tools, air brush etc.

That’s why you need to have end-of-air-line water removal equipment. That equipment can be as simple as a compressed air filter, or more complex, such as compressed air dryers.

What are the parts that make up an air compressor? Understanding about air compressor components will better help you use your air compressor, and make it easier for you to fix when it fails.

This about air compressor components page offers a broad range of topics about air compressor parts. Please scroll the list to find the pages that best describe the compressor information you are looking for.

If the compressor part you need information on is not noted below, please leave us a note at the bottom, and we’ll get information on that part up as quickly as we can.

Did we not answer your question about an air compressor component? You can use the comment section at the end of the page to ask and we’ll try to fix it for you.


Air Compressor Components

air compressor parts and components

Compressor Air Filters

Compressor Air Gauges

Compressor Gaskets

Compressor PRV’s (pressure relief valves)

Compressor Pressure Switches

Compressor Regulators

 Compressed Air Lubricator

Compressor Oil

Compressor Pump Information

Compressor Valves

Air Circuitry & Air Logic


Air Compressor PRV

I had Shane send me in this question recently..

“hi there i have a draper 25lt 2hp 230v i bought second hand its a 2001 model i was wondering if they come with a prv or is that what the safety valve is? and when im done with my compressor and turn it off is the air ment to release itself or am i ment to do it manually? sorry im new to this thanks for your time”

Shane, your compressor better come with a PRV (safety valve)!

What turns your compressor on and off is the pressure switch. If your pressure switch should fail at the cut out pressure setting level (when the tank pressure gets high enough) then your compressor would continue to run, pressure levels would exceed the capacity of the system, and you might experience an explosive type failure. Not nice.

air compressor prv

It is the PRV that will open at a higher pressure setting level than the pressure switch is set for, to blow down the system, and prevent an explosive type failure.

When your compressor reaches cut out pressure, assuming the pressure switch is working (and they normally do), the your air compressor will stop. Whatever compressed air is in the tank will stay there, unless you open the drain valve to drain the tank. This is something that you should do every time you put your compressor away.


Do You Fix Air Compressors?

I gotta tell you folks, there are a ton of people out there looking for a compressor repair location, and places to get compressor parts.

If you or your company is in compressor repair, get you business listed on my compressed air information website. There is no cost, it’s a service to my visitors, and I expect will garner you some visits and earn you some business.

Home Air Compressors

In the northern hemisphere, we’re well into summer now, and for me that means doing a lot more outside jobs, jobs that need compressed air.

Like many folks, I’ve got a small, DIY compressor at home, and I use it pretty regularly. In fact, the uses grow now that I’ve got compressed air handy in my workshop.

home air compressors

So, are you using yours more? If so, don’t forget to check and fill the oil.

As you can see from the photo, there’s oil in my compressor, but I should add just a bit to bring the level mid-point or a little higher than the red dot. That’s what my manual says. Check yours.

If the oil’s dirty, do your compressor a favor and drain the oil, and add fresh compressor oil. It’s good for the machine and will increase the time between maintenance requirements.


Air Compressor Manuals

Question: I just bought my husband a Pro Source 2.5 Peak HP 10 gallon air Compresor 2.0 Continuos Hp. Is there a site I can got to to get a manuel. The store I purchased it at can’t help me, there was no box or pamplets with this one. And I need to know what accessories to buy for him and the kind of oil it uses. Thank you


Hi there…. This seems to be a reoccurring problem for folks trading, buying used, buying new and unboxed, or just misfiling air compressor manuals. You can search this website for available manuals that I (or kind readers) have been able to find, and also a section where you can post a request for a specific air compressor manual.

As manuals become available to me, I upload them to my site and offer them to visitors.


Hayward-Hallett Air Compressor Rebuild

I’ve received a request from a visitor for any information we can provide on the rebuild of an old Hayward-Hallet Air Compressor. I have no personal information to provide.

If you rebuild this type of air compressor, or know of anyone that has information about this type of air compressor, we sure would appreciate it if you could provide that information in a comment. Thank you.

Hello, I am Bill, the Compressed-Air-Man. I have years of experience in industrial and residential compressed air applications, air compressors and general pneumatics. I created this site to help professionals, students, and DIYers understand and properly implement and maintain compress3ed air systems.


  1. Hi Bill,
    I want to know if I was compressing air into a small copper line to a distance of 15 feet, would the gauge on the other end respond quicker or slower if the line was 1/4″ or 1/8″ dia?
    I was imagining that if the airline was small enough to only allow one air molecule to fit at a time, the response would be faster.
    What do you think?

    • I would think the reverse, Tony.
      The larger the air line the faster the compressed air can flow through it, and the faster the pressure build up will be at the gauge or air tool end.
      By reducing the air line size you are both restricting the flow rate, and increasing the friction between the moving air and the I.D. of the tube, creating turbulence and further reducing flow in a small tube or pipe.

  2. Hi Bill,

    Thanks for your answer!

    That compressing air generates heat is clear to me, but to my opinion it is not caused by the simple fact that the space available between the molecules is smaller and that it forces the molecules to rub against each other. When you stop the compressing process while keeping the air at the same (high) pressure the space between the molecules remains the same. When heat was caused by the fact that the molecules are so close to each other it would mean that even after stopping the compressing process, the heating would continue, which is not the case.

    As I said before I do not know much about the physics of compressing air and I found your site by googling in an attempt to learn more about the physics (I am an airgunner that wants to know more about it:) but I do not have the intention to start a scientific discussion. I believe that your explanation is very much sufficient for people that are mainly interested in air compressors.

    I like your extensive way of describing everything that has to do with compressors.

    Kind regards,
    Frie Kil

    • Still got getting your concern Frie.
      Friction is a result of moving objects. When air is being compressed, the air is moving and being forced into a smaller space. That process creates friction in the air molecules RUBBING TOGETHER and that generates heat. Sure, heat from the motor and heat from the pump all contribute to the high temperature of the compressed air as it flows into the compressor tank. Then it cools as there is no heat being generated by the air molecules as they are stagnant.


  3. Although I know little about compressing air your following explanation is not very clear to me:

    “As your compressor jams air into the tank the space available between each molecule of air gets smaller. This forces those molecules of air to “rub” against each other more often, increasing friction. As we all know, friction creates heat.”

    The point is that this situation remains the same as long as the pressure remains the same. This would mean that pressurized air is continuously generating heat, which I can’t believe.

    • Hello there… Frie Kil:

      You say “The point is that this situation remains the same as long as the pressure remains the same. This would mean that pressurized air is continuously generating heat, which I can’t believe.”

      That’s your point, not mine! 🙂

      My point is that as long as the compressor is running heat will be generated by the compressing of the free air. Once the air compressor reaches the cut out pressure setting and stops, the compressor motor, pump, and the air in the tank cools down and the heat dissipates. This, too, is why there is so much water accumulating in the bottom of the tank.



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