Eugene, an avid self-taught DIYer and engineer, has acquired almost 40 years of experience with power/hand tools, plumbing, and woodwork.
A Guide to Using Air Tools For DIY
Air tools as the name suggests are tools powered by compressed air, unlike conventional power tools which are either powered by a battery or a 120/240 volt mains supply. This article outlines the basics of how they work, what tools are available, and how to use them with an air compressor.
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Glossary of Terminology Used With Compressed Air Systems
- CFM or Cubic Feet / Minute The quantity of compressed air which an air compressor can supply or which an air tool requires
- Pressure Air is compressed or "squashed" inside a compressor into a fraction of it's original volume. Air is stored in a tank. The pressure of the air is measured in bar, pounds per square inch (PSI) or kilopascals. 1 bar = 14.5 psi = 100,000 pascals or 100 kPa
- Pneumatics This refers to using compressed or pressurized air
- BSP Thread British Standard pipe thread. Even in countries which use the metric system, the imperial based BSP standard is used (Except in the U.S.)
- NPT Thread National Pipe Thread. An inch based thread used in the U.S.
- Gage (Gauge in UK) In the context of air tools, this refers to the size of a fitting or internal diameter of a hose
What is an Air Compressor and Compressed Air?
An air compressor is a device that squeezes air into a fraction of its original volume, so that it takes up about 8 to 10 times less space. When air is reduced in volume, pressure increases proportionally. So if volume is 8 times smaller, pressure is 8 times higher. This is described by Boyle's Law:
"At constant temperature, the pressure of an ideal gas is inversely proportional to the volume"
PV = constant
How Compressed Air Works
Most workshop compressors are reciprocating types, so they use a piston and cylinder arrangement, driven by an electric motor or engine to compress air. As the air is compressed, it's fed to a storage tank which acts as a reservoir. The tank can deliver a large pulse of compressed air as needed, potentially greater than the pump could deliver on its own.
Portable Air Compressor For Nail Gun or Other Power Tools
What Tools are Powered by Air?
Basically the same tools as are available in battery or mains powered versions....and some others. Some examples:
- Angle grinders
- Nail guns
- Chipping hammers
- Spray guns
- Tire inflators
- Air ratchet
- Impact wrench
Other tools which aren't commonly available in electric versions are:
- Air gun
- Sand blasting gun
- Needle scaler
What Are the Advantages of Air Tools?
- They have a high power to weight ratio. In other words, an air tool will be lighter than a cordless or mains powered tool of the same power rating. Air tools have simple air motors or pistons which are lighter than an electric motor. This is important for assembly workers who may be using a tool all day, and obviously a lighter tool will lessen fatigue
- They are simpler and have less working parts than an electric tool, so there is less to go wrong
- An air tool can be stalled indefinitely. If you stall an electric tool, the back EMF(Electro Motive Force) drops to zero and current flowing through the motor becomes very large. If the trigger on the tool isn't released immediately, the motor can rapidly burn out
- Unlike electric tools which have a universal motor (it can run on AC or DC) which produces sparks at the brushes in contact with the commutator, an air tool is spark-less. This can be a distinct advantage in hazardous environments where there may be gas or flammable liquids
- There is no electrocution risk in damp environments
- Tools are quite slim compared to electric tools with bulky motors. So they can be used in cramped locations (e.g. working on cars)
Do Air Tools Have Any Disadvantages?
Yes they do. However depending on the application or environment, the advantages may outweigh the disadvantages.
- An air hose is required to supply air to the power the tool. This is usually thicker, heavier and less flexible than the power cord of an electric tool. However coiled air hoses are available which may be more convenient e.g. for low powered bench tools
- An air compressor is required, adding to the cost of the system
- Air fed to a tool must be filtered and lubricated to prevent premature wear. If a tool is used infrequently, it can be lubricated with a few drops of oil dropped into the intake port
- Air tools can be somewhat noisy as air exits the exhaust port on the tool
- They are usually more expensive than their electric counterparts
So as you can see, there are advantages and disadvantages to using air tools and there is a time and place for using either a cordless battery tool, a mains powered tool or an air tool. It is not a case of "either or".
What is Required to Build an Air System in a Workshop?
- An Air Compressor. This compresses the air and stores it in a tank. Various types / sizes / capacities are available. The important things to consider when buying are the horse power of the compressor (HP), the delivery rate in cubic feet per minute (cufm) or liters per minute, the tank capacity in gallons or liters and whether the compressor is electric or gas powered. The delivery rate of the compressor should match the flow rate demand of the tool. If it doesn't, you will have to wait every so often for the tank to fill and pressure to build before using your tool again. For tools with a low duty cycle (only used for a few seconds with long pauses in between) e.g. nailers, this isn't an issue. However if you're using a blower, angle grinder etc, the tank can rapidly drain.
- A Filter / Regulator / Lubricator. A filter removes dust and water from air. Dust can scour and damage the working parts of tools, eventually clogging everything up, but more importantly it will cause wear and badly sealing surfaces. When air is compressed, water will condense out (the amount depending on ambient humidity). This water may cause corrosion inside tools if it isn't removed by the filter.
A regulator is like a faucet, controlling the pressure of the air, allowing it to be turned up and down, depending on the maximum requirements of the tool and also the application. A good quality regulator should keep the pressure constant, independent of the air demand of the tool.
A lubricator creates a mist of tiny oil droplets in the air flow, which lubricate moving surfaces in contact inside the tool. When spray painting, obviously lubrication is not necessary and would spoil a finish. For infrequent, short and occasional use, a lubricator is not necessary and a tool can be lubricated with a few drops of oil dropped into the intake port.
A regulator, filter and lubricator can be bought as a single unit, or the modules can be plumbed individually together in various combinations. Sometimes the regulator/filter may be provided with and attached to the air compressor.
You can dispense with all this stuff and just use air straight from the compressor. However water and dust will shorten the life of your tools if you are using them regularly. Tools also have a max pressure rating which can be less than the typical 8 bar / 120 PSI output pressure rating of a compressor. Overpressure could cause damage to a tool, or worse still, rupture. A regulator will drop the pressure to a safe value.
- An Air Hose. One hose is required to connect the compressor to the filter/regulator/lubricator. You then need a work hose to connect to your tool. Various options are available. You can buy a coiled hose (like the coiled cord on a telephone handset), or a non coiled hose. Hoses are usually made from rubber or plastic. Plastic is quite rigid and can crack over time. Rubber is more flexible. Air hoses have various internal diameters. This becomes an issue if you are using a tool which uses a lot of air. A hose with a small internal diameter will cause a pressure drop and less power will be available to the tool. A very long hose will also have the same effect, dropping pressure. This is analogous to an electrical extension cord dropping voltage if it is of inadequate gage or too long when powering a high powered tool which requires high current
- Air Tool. The tool will have a cubic feet / minute (CFM) rating. The air compressor should be cable of supplying this flow rate
Filter Regulator Lubricator Unit (FRL)
Typical Air Tools
Various types of air tools
Compressed Air Nail Gun
Air Tire Inflator
Air Tools Usually Have a Quick Release Push Fit Connector
Sealing an Air Fitting - BSP and NPT Threads
Internationally, air fittings follow the BSP (British Standard Pipe) standard. In the U.S., the NPT (National Pipe Thread) standard is used. Both standards are based on inch measurements rather than metric. NPT and BSP threads differ in profile, diameter for a specific size thread, and pitch. So they are incompatible. It may be possible to mate threads of both types but they may not seal very well, however adapters are available. A pipe thread size refers not to the external diameter of the threads, but originally referred to the internal diameter of a steel pipe for which the thread was intended. Low power tools generally have a 1/4 inch BSP or NPT female port into which a quick release adaptor can be screwed. High power tools such as impact wrenches used to remove bolts from truck wheels usually have larger 3/8 or 1/2 inch ports. Fittings may have tapered threads which become wedged as they tighten, forming a good seal. Air fittings can be sealed using teflon (PTFE) tape. The tape should be wound clockwise looking from the entry point of the fitting. Apply a few layers to form a tight seal.
Links to the BSP and NPT standards on Wikipedia:
Adding an Adaptor to a Tool
This tool was supplied with a 1/4 inch BSP male coupler / nipple which was glued into place. I could have used it with a hose with a female screw fitting on the end, however I wanted it to be quick release so I could easily remove it from the hose rather than having it permanently screwed on.
I could have replaced the nipple in the tool with these adaptors
How to Fit a Connector to a Hose
Fitting a barbed, quick release adapter to a hose. This fitting plugs into the outlet coupler of an air compressor (or the coupler on the end of another hose if you want to get more range)
Reading an Air Gage (Gauge)
The scale on an air gage is marked in bar, PSI, kPa or a combination of the measurement systems
How Do Air Tools Work?
Air tools such as nail guns use a piston and cylinder arrangement just like in an internal combustion engine. Air pressure acting on the large surface area of a piston accelerates it rapidly until it collides with a nail head, driving it forward. Tools such as drills have a rotary air motor. Air pressure acting on the surfaces of the motor give it torque and cause it to turn. Air hammers have a double acting piston which is rapidly moved backwards and forwards as air valves rapidly change the side of the piston which the air acts on
Why is There Water in the Air Compressor Tank?
This happens naturally as air is compressed. Air can only hold a certain amount of water at a given temperature before it starts to condense out. Relativity humidity (RH) is defined as the amount of water vapour in air as a percentage of the maximum amount of water that air can hold at a specific temperature. So 100% RH means air is saturated and 0% RH means it is totally dry. In the metric system. As temperature increases, air can hold more water per unit volume and vice versa. When air is compressed, it takes up less space, and because there is a limit to the amount of water a certain volume can hold, it will eventually condense out if volume is reduced sufficiently. Water vapour density in the metric system is usually specified in g/m3.
2 cubic metres of air at 20° C is at a water vapour density of 7 g/m3. (50% RH at this temperature) The air is compressed by a factor of 10 and allowed to cool back to 20 deg C. How much water condenses out?
The amount of water in the original air is 2 m3 x 7 g/m3 = 14g
When it is compressed, the new volume is 2/10 = 0.2 m3
At 20 deg C, the max amount of water the air can hold is 15 g/m3 (see graph below)
But 0.2 m3 can only hold 0.2 x 15 g/m3 = 3g
So the amount of water that condenses out and collects in the air tank is 14 - 3 = 11g
Safety When Using Air Tools and Compressors
- Wear goggles when using tools which can throw up debris e.g. air grinders, air blow guns and air chisels
- De-pressurise hoses before connecting / disconnecting from tools and compressor
- Don't allow compressed air to blow onto skin or an open wound (This can potentially cause "the bends")
Tool and Compressor Maintenance
- Drain water from a compressor every time it is used
- Check oil level regularly and change oil at intervals as specified by manufacturers recommendations
- Lubricate tools before use by dropping oil into air entry port of tool or use a lubricator. Clean and lubricate moving parts of tools
Power Craft is the registered trade mark of Aldi GmbH & Co. KG
Aldi in no way endorses this article.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: What type of compressor should be used for air sander works like auto or wood?
Answer: You would need to check the spec on the tool for the required cubic feet per minute demand (CFM), then buy a compressor to suit. The problem with using a tool like a sander is that it draws air continuously unlike a nail gun, rivet gun, etc that just takes a pulse of air. So it needs a compressor that can deliver a lot of air continuously or a large tank or both if the sander is going to be used for minutes at a time. Typically a sander will take 2.5 to 5 CFM of air.
© 2014 Eugene Brennan
Joanna on February 25, 2019:
Thank you for this. I needed some quick useful information and you went above and beyond. Very well written!!
Nube Airtool User on January 04, 2018:
Good article, especially on describing use of the filter/regulator/lubricator.
portable air compressor reviews on August 31, 2017:
It is a nice blog.And also informative and important blog.When I read this really I like it.
Instronline on September 10, 2015:
Thanks for sharing this information.This is real great information about air filter ,regulator and lubricant control.This will help us to improve quality of our tools.
Eugene Brennan (author) from Ireland on March 05, 2014:
Thanks for the comments - Hopefully it will help someone out there!........
Writer Fox from the wadi near the little river on March 04, 2014:
Fantastic article! You are a real expert in power tool technology. Enjoyed and voted up!