The Best Air Compressor Tank Size for Blasting: How Many Gallons Do I Need?

By far, the most important factor to consider when purchasing an air compressor is air flow output. This is typically listed in CFM: cubic feet per minute. We’ve got an entire post dedicated to CFM and how it relates to blasting. We highly recommending giving it a read.

The size of a compressor’s air tank tells us nothing about how much air it puts out. To illustrate that point, here is a question to ponder:

Is a car with a 12 gallon fuel tank a fast car?

That is a silly question because it is impossible to answer. You don’t have enough information. Will that car with a 12 gallon fuel tank be right for you and your needs? You can’t make that determination. The size of the fuel tank tells us nothing about the car it is attached to. The same is true when you browse air compressors based solely on air tank capacity in gallons.

That’s not to say compressor air tank capacity isn’t important. It is. It just isn’t very helpful when trying to determine the suitability of an air compressor for any specific task. Let’s take a look at compressor air tank capacity and finish with our recommendations.

The Compressor Air Tank Only Stores Air.

Here in the U.S., when you hear the term “gallons” in relation to an air compressor, you’re usually talking about air tank storage capacity. Note the emphasis on storage capacity. It is important to recognize an air tank doesn’t produce compressed air. It only stores it. For a better understanding let’s take a simplistic look at how an air compressor works.

An electric air compressor consists of three main components:

1. Electric motor
2. Compressor pump
3. Air storage tank

Turn on the air compressor and the electric motor drives the pump that produces compressed air. The compressor pumps compressed air it into a storage vessel. The air storage tank simply stores a reserve of compressed air.

The process continues until the air pressure in the tank reaches a predetermined cut off pressure. Once the air in the tank reaches that cut out pressure, a pressure switch triggers causing the compressor motor and pump to shut off.

As you use compressed air for blasting or running an air tool, the pressure in the air tank drops. Once the pressure drops to the predetermined cut-in pressure, the pressure switch activates again. The motor and compressor pump assembly start running again to produce compressed air. At this point you often need to stop blasting or using the tool to let the compressor “catch up” and refill. Once it does, you begin using air again and the cycle repeats.

Notice the compressor tank simply stores compressed air. It is only one of the 3 main parts of the compressor/ It is the least important of the three when it comes to performance and air output. The heart of a compressor is the pump and motor. They are what produce the compressed air that fills the tank.

Doesn’t a Large Tank Mean a Powerful Compressor?

Not always. You can bolt a huge tank to a small compressor. You can also bolt a huge compressor pump and motor on a tiny air tank. Air tank size tells us absolutely nothing about the air compressor itself or how much air it can produce.

Generally speaking, a new air compressor with a large tank should be associated with a higher output compressor head than its smaller-tanked counterpart. For instance, a large vertical 80 gallon compressor is probably going to have a higher output compressor compared to a portable 20 gallon tank unit. That is a very broad generalization and isn’t always the case. If you’re purchasing a used unit from a private party, it is anybody’s guess. People cobble together some crazy setups. That’s why purchasing an air compressor based predominately on air tank size can be a bad idea.

Let’s go back to our example from the introduction. Shopping for an air compressor based mainly on tank size is similar to shopping for a new car based solely on fuel tank size or the number of doors. Imagine you walk into a dealership and tell the staff you’re in the market for a new ride. The car salesperson tells you they have the perfect car for you. It has a 12 gallon gas tank, 2 doors and costs this much. Do you want it? Is it the right car for you?

You don’t have nearly enough information to make a decision. What size is the engine? There’s a huge performance difference between a 4 cylinder econobox and a supercharged V8. Both can have 2 doors and 12 gallon fuel tanks. When buying an air compressor there are many more important things to consider than how many gallons of compressed air the tank can store.

It is much more important to ensure you’re getting a compressor pump with as large of an airflow output as your budget and power source permit. If you purchase a compressor with an airflow output CFM that can keep up with your needs, tank size becomes much less important.

What does a Large Compressor Air Tank Do?

A larger air tank allows a longer time between compressor cycles. It does not reduce the total time the compressor will be running. For a given air pressure and volume, the air compressor will be running the same amount of time overall.

One common misconception is a compressor with a large tank will have a shorter run time. Some people think upgrading their compressor with a larger tank will decrease the duration of time their compressor runs. It doesn’t. A larger tank does not mean a compressor will be running less time overall. That larger tank simply means your compressor will cycle on and off less frequently.

Imagine we bolt two identical compressor pump and motor assemblies to different tank sizes. We build one compressor with a 28 gallon tank and the other with an 80 gallon tank. Both compressors will run the same amount of time overall when doing the same task. The compressor with the 28 gallon tank will just cycle off and on much more frequently to get the job done.

It’s a very simplistic point of view, but consider the air produced as a simple volume of air. In our theoretical comparison we’re comparing compressors with absolutely identical pump heads and motors producing and consuming the same volume of air. Since both compressor pumps are identical, they produce air at the same rate. Let’s say 12 cubic feet per minute. If we’re doing the same job, air consumption is identical. The only difference in this scenario is the air tank the compressor is bolted to.

The compressor with the large air tank takes longer to deplete than a smaller one. The compressor empties slower allowing more time between cycles. When the compressor does turn on, the 80 gallon tank naturally takes longer to fill compared to the smaller tank.

Obviously, a 28 gallon compressor tank is going to fill and be emptied much faster than the 80 gallon tank in our example. This compressor will cycle on more frequently. However, the time to fill the tank will be much faster.

If you double your air tank size you might decrease the number of times the compressor cycles on and off by one half. However, the duration of each cycle might be doubled since it takes longer to fill the larger tank.

Small Air Storage Tank vs. Large Air Storage Tank

When considering tank size, small and large tanks offer their own unique advantages and drawbacks. Let’s take a closer look.

Small Tank:

• Fills quickly.
• Gets depleted faster than a larger tank.
• More frequent cycling
• Shorter Fill Duration
• Better for low consumption tools that require a small amount of air in short bursts. For example, a 4-8 gallon tank is probably fine for an airbrush or a small brad nailer.

Advantages of a Small Compressor Tank

• Fills quickly
• More portable
• Takes up less space
• Slightly easier to drain

Disadvantages of a Small Air Compressor Tank

• Small tank capacity gets depleted very quickly.
• A smaller tank typically isn’t suitable at all for air tools that demand a lot of airflow or long run duration. For example: abrasive blasting, sanders, die grinders,
• A small tank is typically paired with a low output compressor pump which means frequent cycling. This can lead to premature wear of the motor and pump.
• More frequent cycle means less time to cool. This can lead to hotter air and excess air moisture in underpowered units.

Large Tank:

• Longer Fill Times
• Gets depleted more slowly than a smaller tank
• Less frequent cycling
• Longer Fill Duration
• Better suited for high flow tools and projects requiring a large sustained air supply.

Advantages of a Larger Air Tank

• Larger reserve of pressurized air means you can work longer before the compressor kicks on to refill
• Longer cycle time may keep air cooler and less prone to excess moisture
• Less frequently cycling may extend the life of the compressor motor

Disadvantages of Large Air Compressor Tank

• Takes longer to fill
• Much less portable (Some are stationary and not portable at all.)
• Require more space due to larger size
• Slightly more difficult to drain if you’ve got a manual drain valve at the bottom of a low vertical tank.

Why are larger tank compressors more difficult to drain? They don’t have to be, but the more affordable models usually are unless you upgrade them with a few modifications. The drain valve is typically a simple drain valve located at the bottom or lowest point of the air tank. On a smaller portable compressor you can lift or tilt the compressor up to help ease access. This isn’t possible on a large compressor weighing hundreds of pounds. If all you’ve got is a simple drain petcock on the bottom of a vertical standing 80 gallon tank, you’ll need to bend or kneel down on the floor to open the valve. Automatic drains and modifications are possible to make draining moisture from the tank much easier.

CFM is More Important Than How Many Gallons the Air Tank Is!

Our discussion of air tank sizing helps illustrate how important air compressor CFM output is. On your typical affordable reciprocating air compressor, compressor cycles are controlled by the pressure switch. This switch reacts to the air pressure in the tank. This switch has a preset cut in and cut off pressure that tells the air compressor when to cycle on and off.

Ideally, you need an air compressor that can output compressed air above the rate you’re consuming. Producing more CFM than you need allows the compressor to fill the air tank while blasting or using an air tool. The more your compressor’s airflow output capacity’s CFM output exceeds your needs, the better.

If you’re consuming air at the same rate, or faster, than your air compressor produces it you’ll never fill the air tank with pressurized air to the point the compressor shuts off. The compressor will never be able to fill the tank and cycle off until you stop using air and let it fill. If a compressor isn’t rated for continuous non stop duty it will prematurely fail in this scenario.

How Many Gallons Should an Air Compressor Be for Blasting?

Now for the real question. How many gallons do I need to sandblast? This is one of those questions that is difficult or impossible to answer without more information. We hate to beat a dead horse, but airflow output capacity of the compressor pump connected to the air tank is most important. Don’t worry we do have some recommendations.

Bigger is typically better. Assuming you’re looking at a compressor with adequate CFM output to meet your blasting needs, get the biggest compressor tank you can fit and afford.

In an ideal world, your air tank should be greater than the amount of air required for your pneumatic tool application. That’s good advice and all but blasting demands a lot of airflow. We live in the real world. Budget, space and product availability all come into play.

There is a rule of thumb for sizing a compressor air tank. Like many general rules of thumb, you’ll see about 10 different variations. We’ve settled on our favorite which is based on about 12 years of experience. First, make sure you’ve got adequate CFM output for your blasting needs. Then we recommend your air compressor’s tank capacity in gallons be 6 to 10 times the CFM airflow output.

The absolute least airflow output we recommend attempting to blast with is 10 cfm. You can blast with less. It just takes forever. It is hard on the compressor and it isn’t any fun. We’ll stick with our 10 cfm bare minimum recommendation.

Using our rule of thumb above for sizing an air tank, that puts our recommended air tank size at 60 – 100 gallons.

Bigger is usually better, but 80 gallons or so is realistically all the average do it yourselfer is going to achieve with a typical consumer grade air compressor ready to go within normal budgets. Compressors with larger tanks are available, but they aren’t as common, or as affordable to the average do it yourselfer. Would a 100 or 120 gallon tank be better? Maybe. Is it worth extra cost, effort to obtain, or lost pace? That’s a personal choice. The answer is often no.

What about that Harbor Freight blast cabinet? Do I really need that 60 or 80 gallon tank? Don’t I only need 30 gallons for my blast cabinet? If you take a look at the Central Pneumatic brand blast cabinets sold at Harbor Freight they have a decal on them or the packaging discussing compressor tank size. We’ve provided an example in Figure 1 below.

They essentially don’t recommend a compressor under 30 gallons. Although it is a stupid way to approach sizing an air compressor for a blast cabinet, we do understand why they took this approach. We also agree with their assessment but for less direct reasoning.

By now you know air tank capacity isn’t very useful when discussing compressor performance. We believe Central Pneumatic is taking an indirect approach to recommending the amount of airflow you need for their blast cabinet guns. They’re doing it with gallons instead of airflow output in CFM. Why? It is easier. The tank capacity in gallons is usually pretty apparent and readily accessible to consumers and retailers. Finding the specs on an air compressor’s true airflow output is often a little trickier. The manufacturer is relying on compressor generalizations we mentioned earlier to help make things easier.

Compressors with a tank larger than 30 gallons are likely going to have higher output compressor pump heads. This makes them more suitable for blasting. Any readily available compressor with a 30 gallon or smaller tank is almost always going to have a low output 110V compressor attached to it. This may work for short blasting bursts but isn’t recommending for abrasive blasting.

Conclusion:

We’ve covered a lot here so let’s recap. Here are the 3 main takeaways from this article:

• Air flow output in CFM or SCFM is the most important factor to consider when choosing an air compressor for your blast cabinet.
• Air tank size in gallons should be 6 to 10 times the airflow output (CFM) of the air compressor. (A compressor with an output of 10 cfm should have a 60 – 100 gallon air tank.)
• When considering air tank capacity, we recommend a 60 to 80-gallon air tank or bigger for blasting.

Bigger is typically better, but 60 to 80 gallons is typically the the largest range of air tank sizes you’ll find in most consumer or homeowner grade air compressors. Blasting with a smaller air tank is possible but if you’re using an underpowered compressor it is is ill-advised.

Remember, a larger compressor air tank simply offers a larger reserve buffer of air. Compared to a smaller air tank, this allows you to use your blast cabinet or air tool for longer before the pressure drops and the compressor turns on. Once the pressure drops to the cut in pressure, the air compressor turns on and refills. The larger tank takes longer to refill compared to a smaller tank. A larger tank decreases the frequency of cycles but increases cycle duration. With everything else equal, the overall time a compressor spends producing a set volume of compressed air stays about the same regardless of tank size.

By now you’re probably realizing choosing the right air compressor for your blast cabinet is a little more complex than comparing gallons of tank capacity. You’ll need to match a unit with your air flow output needs, electrical power requirements and much more. Fortunately, we’ve got your back! This post is part of a series of articles we wrote to help sort it all out. Check out our “10 Key Factors to Consider” air compressor post for a great crash course to get started!