Air Compressor Guide
What is an Air Compressor For?
From spraying miniature figures to shot blasting body panels, inflating tyres to filling scuba tanks, an air compressor has a multitude of uses. An air compressor is often a vital bit of kit in any workshop however picking the correct one to run all of your air tools and plasma cutter can often or not be a difficult task.
Types of Air Compressors
On all of the portable air compressors listed on our website, we do what we can to provide as much information as we possibly can, but what does some of it mean? What is FAD and CFM and how does it effect your tools? In this guide, we will do our best to cover as much ground as we can so you have a a much better understanding of which compressor is ideal for you.
We supply a comprehensive range of portable air compressors for all of your air feed requirements. Our air compressors are from FIAC, who are known for there outstanding quality and reliability. Offering a wide range from industrial to DIY, we offer direct drive, belt driven and rotary screw units in 240V, 415V and Petrol driven models. We also supply a range of air compressor hoses and PCL fittings so we can provide you with a total solution.
Delivered direct to your door normally on a 2 days service to UK mainland, 3-4 days for Highlands and Off-shore locations.
Displacement (volume)
This term is used to decide the theoretical volume of a compressor, i.e, the swept volume of a cylinder multiplied by the number of compressions in a minute and expressed in cubic feet per minute (CFM). This figure should not be used in calculating the size of compressor required, as it bears no relationship to the free air figure that you may require.
Free Air Delivered (FAD)
This measurement is the volume of air taken into a compressor and therefore describes more accurately the volume of air available for use. Expressed as CFM/FAD at a given pressure. Remember, Displacement is the theory and CFM/FAD is the actual volume available.
Pressure
This is the way force, e.g., in the compressed air system is expressed and is measured in either pounds per square inch (psi) or bar. Pressure is important because to have too low a pressure would cause the equipment not to work correctly, too high a pressure would at best rapidly wear out the equipment, at worst it could make the equipment lethal.
Single Stage Compressors
One or more cylinders producing the final pressure in one compression. Normal maximum pressure 150 psi.
Two Stage Compressors
First Stage: Air is compressed to approximately 30 psi, cooled then compressed to final pressure in the second stage Normal maximum pressure 200 psi. Note: Two stage provides more air for less energy.
Cost of Air Leaks
Hissing hoses are present in most warehouses you visit. Hissing hoses are a length of air hose which has become frail or damaged, and will be costing its owner a small fortune, but how much is in energy is it actually costing?.
An air leak size of 0.75mm in diameter will lose 1.6 CFM and 300W of energy. An air leak which is 1.5mm in diameter will be losing 6.5CFM and will use 1100W of energy.
Power Supply
Single Phase
Standard supply for domestic and light industry 230V.
5Amp Light Circuit - Not suitable for the air compressors
13Amp Ring Main - Max 2.5hp std Compressor, Max 3.0hp for LC Compressors
45Amp Cooker/Shower - Max 3.5hp Compressor
The main benefits of a single phase compressor is that they can be used without much worry with if your power supply will run the machine. They also hold there second hand resale value.
Three Phase
Main electrical supply to industry.
400v - Will run any sizes of compressor
The main benefits of three phase is that they save approximately two thirds on energy over single phase compressors. They also have a stable supply to the unit which in turn offers a much longer motor life.
Air Equipment Consumption Guide
| Tools | FAD/CFM | PRESSURE (PSI) |
| 3/8" Impact Wrench | 2-3 | 70-90 |
| 1/2" Impact Wrench | 4-6 | 70-90 |
| 3/4" Impact Wrench | 9 | 70-90 |
| 1" Impact Wrench | 14 | 70-90 |
| 3/8" Ratchet Wrench | 2-5 | 70-90 |
| 1/2" Ratchet Wrench | 2-5 | 70-90 |
| 3/8" Drill | 5 | 70-90 |
| 1/2" Drill | 12 | 70-90 |
| DA Sander (top quality) | 10 | 70-90 |
| DA Sander (econ. model) | 20 | 70-90 |
| 7" Sander/Polisher | 25 | 70-90 |
| Zip/Impact Cutter | 4-5 | 70-90 |
| Cutter Shears | 4-8 | 70-90 |
| 4" Angle Grinder | 18-25 | 70-90 |
| 7" Angle Grinder | 25-35 | 70-90 |
| Tyre Inflator | 2-4 | 150-230 |
| Tyre Changer (Manual) | 4 | 150 |
| Tyre Changer (Auto) | 6 | 150 |
| Sand Blast Cabinet | 10-50 | 50-100 |
| Sand Blast Hand Gun | 8-12 | 100 |
| Spray Guns: | ||
| Airbrush | 0.25 | 30 |
| Miniature | 4-7 | 20-50 |
| Low Pressure | 1.7-4 | 20-40 |
| Standard | 7.14 | 50-60 |
| HVLP | 14-20 | 70-90 |
| HA/GEO/9000 series LVLP | 7-9.5 | 28-36 |
| Air Fed Mask | 5-6 | 20-40 |
| Oil Pump | 1.5 | 100-150 |
| Grease Pump | 4.5 | 100-150 |
| Air Water Wash | 10 | 150 |
| Car Wash | 1.5-5 | 70-100 |
| Blow Gun (safety nozzle) | 3 | 100 |
| Spark Plug Cleaner | 3 | 100 |
| Underseal Gun | 4 | 100 |
| Rivet Gun | 1.5-3 | 70-90 |
| 2 Ton Air/Hydraulic Lift | 5-8 | 130-150 |
| Brake Tester | 3-7 | 75-100 |
| Plasma Cutter | 6-8 | 60-100 |
Please Note, the figures in the table are only a guide and for additional information, we recommend contacting the supplier of the tools or giving us a call on 01452733933.
Choosing the Right Compressor
Three-phase compressors are more efficient producers of compressed air than single-phase equivalent units, so where a three-phase supply is available the best option is the three-phase compressor. Single phase compressors up to 2.5 HP can operate from a 230V 13A power supply, with the exception of the new 3HP low current models. 3.0HP and above must operate from a 230V 30A supply. Wherever possible choose a larger compressor than you require at present to allow expansion. Compressors with cast iron cylinders running slow, offer a much extended service life.
Bodyshop - using the air equipment consumption guide, add all the equipment consumptions together and divide by two, the resulting figure is the minimum free air you require.
Workshop - using the air equipment consumption guide, add all the equipment consumptions together and divide by three, the resulting figure is the minimum free air you require.
Note for calculation purposes, always use free air delivered figure.
Compressor Size Guide
Ask Yourself -
1 What is the air to be used for?
2 What is the maximum pressure required? (see consumption guide)
3 What electricity supply is available? (single/three phase)
4 What size compressor is currently in use? (See calculation guide below)
5 How well does the existing compressor cope?
6 What are the future plans for additional staff/ equipment?
Calculation Guide (approx) -
Multiply motor HP by 3.3 = output in CFM/FAD
Multiply motor kW by 4.5 = output in CFM/FAD
Multiply motor kW by 2.1 = output in L/Sec /FAD
Hose Selection
An air tool needs the following:
A) Correct size of compressor to ensure sufficient air available
B) Correct size of air hose to ensure minimal pressure drop and air flow
C) Correct pressure at tool (see chart)
D) Correct type of lubricant (Not engine oil)
E) Clean dry air (use filters, regulator, dryer and lubricant)
Recommended Air Hose Sizes
| Hose | Uses | Max Flow CFM |
| 1/4" | Tyre inflators / Airbrush | 5 |
| 5/16" | Std Spray Guns / 3/8" Drill / Ratchet Wrench | 15 |
| 3/8" | HVLP/LVLP Spray Guns / 1/2" & 3/4" Wrenches/Sanders | 25 |
| 1/2" | 1" Impact Wrenches | 50 |
Helpful Tip: Always keep hose length as short as practical. eg. 1/2" impact wrench with20 metres of 1/4" bore hose will develop less than 40% of its available power!