Air Compressors Guide

Machine Mart have been a leading supplier of Air Compressors in the UK for almost 50 years and have created this brief guide to help you understand the terminology and make the best choice.

Advantages of using air compressors and pneumatic tools / air tools are:

  • A safe alternative to electric tools - no chance of electric shocks.
  • More powerful than conventional electric power tools.
  • Deliver higher torque and more revolutions per minute to speed the job up.
  • Versatility to be able to use multiple tools with one Air Compressor and at the same time.
  • Energy efficient for multiple tools
  • Quiet Running. Normally if there is an electric power tool available to do a task then doing it with air is also normally an option. To successfully choose the correct air compressor you need to think about where and what you want to use it for. Machine Mart stocks a comprehensive range with models suitable for the smallest DIY task to heavy duty industrial machines. 

If you have ever had a tyre changed, an air compressor would have been involved in the process. From the impact wrench undoing your wheel nuts, to the tyre inflator pumping up your tyres.

The possibilities are endless. Remember, if you can do it electrically, you can normally do it pneumatically.

BUT REMEMBER - YOUR AIR IS NOT UNLIMITED SO CHOOSING THE RIGHT COMPRESSOR IS IMPORTANT.

Air Compressor Uses

Domestic/DIY
Common uses of an air compressor in a DIY environment include nailing and stapling, drilling, tyre inflation, air brush painting and blow cleaning.

Generally, the home user main concerns are about physical size, price and power supply constraints.

The compressor will not usually be expected to supply large volumes of air on a continual basis and only one tool will be in use at a time. The electricity supply available should also be considered as larger air compressors require a substantial amperage supply.

For this reason Machine Mart would normally recommend a smaller unit for the home enthusiast. These smaller machines usually have wheels and handles to assist with manoeuvring. Consideration should be given to the “voltage drop” created by long extension leads. Air compressors require a high initial current supply to start working and problems sometimes occur when the length of cable reduces its capacity to supply sufficient power.

Commercial
A professional air compressor user will probably have different selection criteria – the capacity to supply the tools required is more important than the price and a large power supply can be laid on to suit the air compressor if necessary.

Commonly the commercial user will choose a machine with a larger tank and higher horsepower. Due to the size and the fact that larger air compressors have to be hard-wired in, only the smaller models will be fitted with wheels. Anti - vibration mountings are available for the static models to reduce noise levels.

Machine Mart also sell small easily portable air compressors which are suitable for service engineers, upholsterers and other mobile users. Large, petrol and diesel engine air compressors are also available for applications where there is no electricity supply.

What applications do you have in mind?
Nailing or spraying applications require widely varying amounts of air, depending on the capacity of the tool in question. Small, occasional, tacking jobs can generally be supplied by quite compact air compressors. While firing large nails with a large internal piston repeatedly will require a large volume of air. For paint spraying, because this tends to be a continuous operation (i.e. a constant air flow to ensure the paint gun operates but also to produce the correct atomisation for the paint) you will require a large air supply and a powerful air compressor, depending on the spray gun nozzle selected.

Frequently Asked Questions About Air Compressors

What is Air Consumption?
It’s the volume of air needed to make the air tool work for a length of time.

What are PSI & bar?
PSI and bar are both a measurement of pressure. PSI is expressed in pounds of force Per Square Inch (PSI).  14.5psi = 1 bar of pressure. This is the amount of pressure exerted on a square inch of something solid. If you increase the pressure then more force is being exerted through the airline, a higher pressure will also increase the volume of air travelling through the airline.

What is CFM?
(Cubic feet per minute) This is the volume of air produced by the air compressor at the pump, measured in cubic feet per minute, with no losses being calculated (Displacement).

CFM is normally expressed in one of two ways:

  1. CFM Displacement - This is the measured bore and stroke of the air compressor cylinder, but not the output.
  2. CFM FAD – Free Air Delivered.

What is Free Air Delivery? 
This is the amount of air being produced (use-able air) from the outlet tap of the air compressor including the losses. Since air compressors are not 100% efficient, Free Air Delivery (FAD) is normally 30% less than the displacement CFM figure. This MUST be taken into consideration when calculating your requirements.

What is the Average Air Consumption when referring to air tools?
The average air consumption figure for an air tool shows the output required from the air compressor to power the tool, on an “average work cycle”. This figure assumes that you will use the air tool for only 25% of the time, on average (i.e. 15 seconds in every minute).

If you need to use the tool in question continuously, you should buy an air compressor capable of supplying FOUR TIMES the air supply required by the tool.

The DUTY CYCLE of your compressor should not run more than 10-12 times an hour as the air consumption will reduce, so it’s important this is considered at design infancy.

I am setting up a body shop, what compressor do I need?
If you have a 3 phase supply, a single phase unit will not be large enough. How many sanders will you be running at once? Are you using an Air Fed Visor? What size spray gun nozzles will you be using and how many guns will you be using at once?
For a professional body shop we recommend a large piston (reciprocating) type compressor or a rotary screw compressor (particularly if constant use is required)

I need an air compressor that is approximately 50cfm?
We would advise a screw compressor of this size with a built in drier to ensure your air comes out of the unit completely dry.

https://www.machinemart.co.uk/c/screw-compressors-dryers-filters/

I have a small garage at home with a 20A consumer unit fitted. What’s the largest compressor I can have?
You have quite a lot of choice depending on your budget. You could have any of our compressors up to a maximum of 2 horse power. What tank size you can have will just depend on how much room you have in your garage.

You have so many air compressors and they all differ in price, I don’t know which one to pick? I need one for my garage to do some model air brushing and my husband can pump tyres up etc. I have around £110 to spend can you help?
There are so many variants that people require depending on budget, space, power supply and air consumption requirements. The Tiger 8/250 will be able to handle all of your tasks mentioned and is within budget.

https://www.machinemart.co.uk/p/clarke-tiger-8250-2hp-24-litre-air-compressor/

Can you use a sand blaster on a 14cfm compressor even though it says 6cfm on the sandblaster?
Using our calculations the 6cfm will be for an average air consumption so you will need 4 times this amount to calculate the compressor size. We would advise the following air compressors which are available in both 1 phase and 3 phase:

https://www.machinemart.co.uk/p/clarke-xe37200-ol-industrial-air-compressor-23/ or https://www.machinemart.co.uk/p/clarke-xe25200-industrial-air-compressor/

What does voltage drop mean?
The copper core (the resistance) in the cable causes the voltage to dissipate across the cable. In other words the longer the cable, the higher the resistance, so the voltage (power) has to work harder to get through it. Ideally any air compressor installation needs to be as close to the main consumer unit as possible. Feel free to come back to us if you need any advice on your requirements should you need any help.

Why do I need anti-vibration mounts on my compressor?
This is so any vibration in the unit doesn’t go into the delivery pipe or any of the metal structure that could resonate or vibrate. This includes the legs of the compressor or the pipe work. Also we would advise to ensure you fit a flexible pipe between the tank and the pipe work so the vibrations are absorbed at the machine.

Where should I contact if something breaks or I need to get my compressor serviced?
You call us on 0871 410 1270 (8.30-6.00pm Mon-Fri and 8.30-5.30pm on Saturdays) or alternatively, email us on technical@machinemart.co.uk and we will respond within 2 working days. 

Extra Help Choosing the Right Air Compressor for the Job

Piston Driven Air Tools require a smaller amount of air whilst Abrasive Air Tools require a larger amount of air through the friction from the sanding. Spray guns will also require a larger amount as this is an open air line.

Compare the list of applications below with the recommended air pressure and consumption required.

Air Tool

Air Pressure (bat)

Average Air Consumption (CFM)

Air Drill

6.2

4

Angle grinder 4"

6.2

6

Angle sander 7"

6.2

5

Caulking gun

6.2

1

Chisel/Hammer

6.2

4

Cut off tool 3/8"

6.2

4

Die Grinder

6.2

8

Dual action Sander

6.2

6

Dual action sander

6.2

6

High Speed saw

6.2

5

Hydraulic Riveter

6.2

4

Impact wrench 1"

6.2

12

Impact wrench 1/2"

6.2

4

Impact wrench 3/4"

6.2

7.2

Impact wrench 3/8"

6.2

4

Long Bed sander

6.2

8

Mini Die Grinder

6.2

8

Needle Scaler

6.2

4

Orbital sander

6.2

6

Punch and flange tool

6.2

0.3

Ratchet 1/2"

6.2

6

Ratchet 1/4"

6.2

3

Ratchet 3/8"

6.2

4

Shears

6.2

5