Compressed Air Impact Wrenches vs. Electric Impact Wrenches

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Compressed Air Impact Wrenches vs. Electric Impact Wrenches

Impact wrenches are most often thought of as tools for automotive repair work. Mechanics regularly use them for taking apart stubborn bolts, increasing their productivity. However, while automotive repair is probably the most common use for impact wrenches, it is not the only one. They are also used for manufacturing and even for construction. In any situation where a powerful wrench is needed to take off or put on nuts and bolts, an impact wrench is the tool to use.

Impact wrenches can be either compressed air-powered or electric-powered; the best type to use depends on the application and type of power available.

This guide will explain how impact wrenches work, the different types of impact wrenches, and the main differences between compressed air impact wrenches and electric impact wrenches.
 

How Impact Wrenches Work

Impact wrenches look somewhat like electric drills, but other than looks, these two types of wrenches do not have much in common. While a drill supplies constant rotational power at a relatively high speed, an impact wrench is designed to provide high torque at a low speed.

Actually, the impact wrench does not even provide constant torque. Instead, it is more akin to putting a wrench on the nut or bolt that needs to be loosened and hitting it with a hammer, turning it in small, incremental stages. As power is applied to the impact wrench, an internal "hammer" strikes against an anvil, which is connected to the square drive on the business end of the wrench. This attempts to force the tool (usually a socket) that is attached to the air drive to turn.

The great advantage impact wrenches have over other tools is this hammering action, which does two things. First, it applies more force than can be applied with a typical wrench, or even a breaker bar. Second, the hammering action tends to break loose rust and other things that can cause a nut or bolt to stick.
 

Three Types of Impact Wrenches

There are three types of impact wrenches: one that is driven by compressed air (pneumatic), and two others, both of which are electric. Electric impact wrenches can either be corded, using regular 120 VAC house current, or cordless, powered by rechargeable batteries.

Pneumatic Impact Wrenches

The more traditional type of impact wrench is pneumatic, i.e., powered by compressed air. These require an air compressor to provide compressed air as the motive power for the impact wrench to work. A fairly large air compressor is needed, as the air consumption of a pneumatic impact wrench is rather high.

Air-operated impact wrenches come in 0.25-inch, 0.375-inch, 0.50-inch, 0.75-inch, and 1-inch drive sizes. The drive size refers to the square drive where the tool is attached. The larger the drive size, the more torque the tool can provide. One-inch drive torque wrenches can provide as much as 3,000 feet/lbs of torque.

Pneumatic impact wrenches allow continuous use for the entire day, as long as air is provided. While the most common configuration is the traditional pistol-grip model, they also come in compact models for working in tight spaces. These basically consist of the motor and impact mechanism (hammer and anvil) with a butterfly switch to operate them. Mechanics who have this type of an impact wrench generally only use them for tight spaces, as they are harder to hold onto than a pistol-grip impact wrench. Standard pistol-grip models of air-operated impact wrenches are more compact than electric impact wrenches.

The biggest disadvantage to pneumatic impact wrenches is that it is hard to control the power on them. They do not have variable-speed triggers, nor is the amount of power they provide easily adjusted. These tools are for breaking things loose or tightening them very tight. They do that well, but if a small amount of power is needed, such as for loosening a stubborn screw, they will provide too much power, either breaking the screw head off or stripping it out.

Corded Electric Impact Wrenches

Corded electric impact wrenches are rather rare, with the focus in recent years shifting to cordless ones. However, several manufacturers still produce corded electrical impacts. These provide similar performance to pneumatic impact wrenches of the same size, although they are only available in limited sizes. Corded impact wrenches are only available in 0.75- and 0.50-inch sizes.

The body of a corded electric impact wrench is generally slightly longer than that of a comparable pneumatic impact wrench. This is necessitated by the electric motor, which must be larger than a corresponding pneumatic motor of the same force. However, other than in tight work areas, they are about equivalent in convenience.

The great advantage of corded electric impact wrenches over pneumatic ones is that a compressor is not needed. They can be used anywhere that electric power is available. However, if there is no electric power available, they are worthless. While an air compressor can be charged with air and then taken to a remote location for use, similar to a battery, there is no equivalent way to use corded electric impact wrenches in remote locations.

Cordless Electric Impact Wrenches

Cordless electric impact wrenches are part of the general move from corded electric power tools to cordless. These tools are powered by lithium-ion (Li-ion) batteries, ranging from 18 volts to 28 volts, depending on the manufacturer and model. Li-ion battery technology provides much more power in a battery pack than older rechargeable battery technologies, allowing the tool to be used longer between recharges. Li-ion batteries also recharge much faster than older types of rechargeables.

There are two basic problems with cordless impact wrenches. The first is that the amount of power drain required drains the batteries quickly. This power drain takes the form of high current draw and long duration of operation. While nickel-cadmium (NiCad) batteries are better for dealing with high current draw, Li-ion batteries are better for long duration of operation.

The second disadvantage of cordless impact wrenches is that they are generally less powerful than corded electric or air-driven impact wrenches. The most powerful cordless impact wrenches can provide the same amount of power as the other types, but most only produce about half the power.

While there are disadvantages to cordless impact wrenches, they do have one major advantage, which is portability. Since they need no external power source, they can be used anywhere. This makes them ideal for on-the-road repairs or for working on construction sites where there is no electrical power available.

Of all the types of impact wrenches available, cordless ones are the best choice for use in removing over-tightened or rusted screws without stripping them out. The lower torque, coupled with greater trigger control, makes it possible to use these impact wrenches for more delicate applications.
 

Selecting Air or Electric Impact Wrenches

The decision to purchase air or electric impact wrenches depends on the individual's needs, electric or air power availability, price range, size, and intended use.
 

 

Pneumatic

Corded Electric

Cordless Electric

Power

Excellent

Good

Not always good

Sizes Available

0.25-inch, 0.375-inch, 0.50-inch, 0.75-inch, 1-inch

0.375-inch, 0.50-inch

0.25-inch, 0.375-inch, 0.50-inch

Convenience

Needs air compressor

Needs electric power

Self-contained (best)

Cost

Lowest (without air compressor)

Medium

Highest

Physical Size

Smallest

Larger

Largest

Safety

Air cannot electrocute

Cut lines can cause electrocution

No risk of electrocution


There is no clear winner as to which type of impact wrench is the best for all applications. Rather, much of this decision depends on whether the individual is already using air tools, and whether they need to have a portable impact wrench.


Using Impact Wrenches

There is some danger involved in using impact wrenches. The amount of force they apply to loosen tight fasteners is extensive. It is sufficient to cause fasteners and tools to break. Never use impact wrenches with standard sockets, which are designed for use with ratchets; only use them with impact sockets. Standard sockets can shatter when used with impact tools. Impact sockets have thicker walls and are made of slightly softer steel, so that they will not shatter as easily.

It is also important to wear the proper safety protection gear when using these tools. Protective goggles and gloves should be worn to prevent injuries.

All air tools require regular oiling to function properly and avoid damage. A couple drops of air tool oil (a light machine oil) in the air inlet before using it is sufficient to lubricate the tool and keep it working properly.
 

Buying Impact Wrenches on eBay

eBay is a great place to shop for impact wrenches due to the wide assortment of wrenches and convenient buying options available. While there are quite a number of all three types of impact wrenches available on eBay, they are not all located in the same place. Impact wrenches can be found in the following eBay categories:

Another way to find impact wrenches on eBay is by doing a simple keyword search for "impact wrench" or for one of the three types. If you are looking for air-driven impact wrenches, you can use either "air-impact wrench" or "pneumatic impact wrench"; however, the results for these two searches will not be exactly the same.

When buying used impact wrenches of any type, it is a good idea to get some sort of guarantee from the seller that it will not be dead on arrival. While these are rather robust tools, it is possible for them to be damaged if they are not properly maintained. That said, with the thousands of reputable sellers in the eBay marketplace, you should not have any problem finding a quality new or used impact wrench on eBay, as long as you pay attention to the sellers' feedback scores and communicate with the seller to find out whether they offer a guarantee (if none is mentioned in the listing).
 

Conclusion

Impact wrenches are incredibly useful tools for removing stubborn bolts and nuts, especially if they have become rusted on or are overly tight. The hammering action of the impact wrench can serve to loosen rust and remove nuts and bolts that are otherwise impossible to remove.

There are three different types of power impact wrenches: air driven, corded electric, and cordless electric. Of the three, air-driven is by far the most common, available in the most models and sizes. To use them requires the availability of a fairly sizeable air compressor. Neither corded nor cordless electric impact wrenches require an air compressor, although corded ones do require access to electrical power.

Cordless impact wrenches provide the most convenience and portability, but are the most expensive option. Most models of cordless impact wrenches are also considerably less powerful than the other two styles, delivering about half of the torque.

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