How To Drain An Air Compressor

image of air compressor drain valve positionProper compressor maintenance is an essential part of increasing the lifespan of your air compressor.

This includes cleaning the external parts of the unit, checking the gauges and valves for any visual defects, as well as air compressor tank draining.

Fortunately, whether you have a smaller 5-gallon compressor or an industrial-sized 60-gallon air compressor, the process of draining the tank is virtually the same.

At ToolTally we’re big on not only helping you get the right tools, but also helping you maintain them. In the following article, we’re going to look at why you need to drain the moisture from your tank, as well as explaining in three simple steps how to do so.

The Issue with Water in Your Compressor tank

When your air compressor pressurizes the surrounding air, the water vapor or humidity can be condensed as water. This water then sits in the bottom of your tank. 

The main issue with having water in your air compressor’s tank is that it can cause the tank to rust from the inside out, weakening the walls. 

This can be extremely dangerous because the tank will still appear to be in good working condition, and it will likely still work properly, however, the structural integrity of the tank will be compromised. 

Notice how this compressor blew out from the bottom where the rust and water collected

Most people assume that this will simply cause a slow air leak once the metal has been rusted through, but as can be seen in this video, a compromised compressor tank could possibly lead to an explosion, which could cause severe and potentially fatal injuries.

There are, of course, less serious issues with having water accumulate in your compressor’s tank. For example, water and/or rust could potentially travel from the tank, into the air hose, causing damage to the air tools you’re using.

With large compressors that shops use, there is typically an external device that serves as an air regulator, air dryer and sometimes even sends oil into the air line. It is tempting to expect this external air dryer to handle all of the moisture. However, on days with a high relative humidity, it is possible for even the dryer to become overwhelmed. Bleeding the water out of the air tank preserves the entire system and lengthens the lifespan of all your air tools

Furthermore, the amount of water in the tank could affect its capacity. Therefore, the pressure gauge could give you a false reading, which could be dangerous, especially if it’s reading a lower internal pressure when it is, in fact, already above its capacity.

When you empty the tank, it lets your tank start off at the factory setting of pressure and makes your compressor more energy efficient since it doesn’t have to overcome the water pressure.

image of older rusted air compressor

How To Drain Your Air Compressor

As you can see, water inside your compressor’s air tank is no laughing matter. So, how can you avoid this annoying issue?

Below, you’ll find the three steps that are involved in properly draining your air compressor tank.

Step 1
The very first thing you’re going to want to do is to ensure that the compressor is turned off.

While this can be done by simply making sure the switch is turned to the off position, we recommend that you also unplug the unit to ensure that it’s in a zero-energy state and poses no threat to you while working on it.

Step 2
The next thing you’re going to do is reduce the tank’s internal pressure to somewhere below 10 PSI.

For this, there should be a ring on the tank’s safety valve, which can be pulled to release pressure. It’s a good idea to deflect the air by using your free hand, while the other hand pulls on the release valve. Do this until the tank in emptied.

We recommend wearing eye protection while doing this since the release of pressure could cause debris to fly into your eyes.

Step 3
Next, you’re going to need to locate the tank drain valve. This should be situated somewhere on the bottom of the tank.

Once located, open the drain valve, which will allow any internal moisture to escape. It’s a good idea to tilt the tank to ensure that all moisture has a chance to drain out.

When the tank is fully drained, you’re free to close the valve and begin using your compressor as normal.

image of compressor covered in dust

Frequently Asked Questions

Below, you’ll find some of the most commonly asked questions surrounding moisture in your compressor’s air tank.

Why is there a drain on my air compressor?

All air compressors are fitted with a small water drain to allow any moisture that accumulates inside the tank to be drained out. On gas-powered air compressors, it also allows you an easy way to bleed out pressure to make it easier for the engine to start. 

Can I Run My Air Compressor With The Drain Open?

There are very few reasons why you would run to run the air compressor for a long period of time with the drain open. 

Running with the drain open prevents your compressor for building pressure and can — if done for too long — cause the compressor to burn out.

Some folks will run their tanks with the drain partially cracked. This is especially handy when trying to paint a car or power a sandblaster. In each of these scenarios, you are going to run the air compressor a little more, and water can be harmful to the project. Slightly opening the drain can allow that water to run off while you work and provide you with a more dry source of air. 

Working with the drain slightly opened is not a replacement for using an air dryer. 

Should I store my compressor with the drain open?

There is no right or wrong answer to this question, but there are staunch opinions on both sides of the camp. 

As long as you are frequently draining the tank, then you are doing what needs to be done in order to prevent the tank from rusting. 

While storing it with the drain valve open does provide the best chance for any residual water to drain out, it also makes it possible for spiders and other creepy crawlies to move into the tank. That dust and dirt that they bring in can get into your airlines and cause problems.

I’m in the camp that thinks you should drain the tank out, and then close it up once most of the water is out. 

One thing that is funny, is when someone forgets that they left the drain valve open, and they can’t figure out why their compressor isn’t airing up. Now that is funny as shit. 

Where does the water come from and how much water will my tank generate?

As you know, whenever air is compressed inside a tank, the pressure will increase. But when there is a significant amount of moisture in the incoming air, the pressure will cause this vapor to condense, which will cause water droplets to form inside the compressor’s air tank.

Generally, the longer a compressor is run, the more moisture will have time to accumulate inside the tank.

Do I need to drain my air compressor tank?

Yes!

By allowing water build up inside your compressor’s air tank, the metal will eventually begin to rust, which can cause damage to the tank’s structural integrity.

At best, this will cause the tank to leak. However, it could also cause the tank to explode when under pressure, causing severe and potentially fatal injuries.wa

How often should I drain my air compressor tank?

There is no need to drain your tank at every single use, however, we recommend that your tank be drained once every couple of days if it’s used daily. 

If you drain it once a week, you should be doing everything that is needed to prevent major rust. 

On the other hand, if you only use your air compressor every now and again, it’s best to drain the tank after every time it’s used.

Always remember that leaving moisture in the tank can cause it to rust from the inside out. In other words, moisture will cause damage that’s not visible from the outside.

If the shop is closing up for the weekend or a holiday, it makes sense to drain the tank to prevent any standing moisture. 

Where is the Compressor tank drain located?

All air compressors are fitted with an external drain valve. These are typically located on the bottom of the tank to easily allow moisture to escape once the valve is opened. 

Do you need to tilt your compressor when draining?

Depending on where the drain valve is located, you may or may not need to tilt the tank to drain it properly.

On smaller units (perhaps with a 6 gallon tank or smaller), we recommend tilting it to ensure that the moisture from both ends of the tank have a chance to escape through the drain valve.

Otherwise, the escaping air and pressure will get most of the water out 

Automatic Tank Drains

Having an automatic tank drain can be very beneficial, especially if your compressor is used for larger industrial applications where you might be too busy to drain the compressor tank with timed water purges.

Mainly, an automatic tank drain allows accumulated moisture to escape with each burst of compressed air, instead of needing to drain the tank manually. Not only does this allow the moisture to escape, but it also prevents rust particles from being able to get into your tank’s filtration system.

This translates to less maintenance, as well as longer filter and compressor lifespans and higher quality compressed air for the power tools that you use.

Zijia 1/2" Automatic Tank Drain

image of automatic tank drain

From Zijia Tools comes their ½” automatic tank drain. It has an L-shaped structure and is equipped with a ball-valve filter and adjustable drain valve.

The unit is extremely handy and is an AC 110V two-way, direct-acting auto drain that will automatically ensure that your air compressor is kept free of moisture at all times.

In other words, you’ll no longer need to worry about moisture building up inside of your air compressor: the Zijia ½” automatic tank drain will do all the work for you! and help extend the life of your expensive air compressor.