Add Another Air Tank

Why add another air tank to your air compressor? What are the ramifications?

This is page two of an article about I need more air! Page one about I Need More Air is here. Page one begins our discussion about the benefits of adding another air tank.

If an air tool draws more air than the air compressor can deliver even when running full out the supply and pressure of compressed air to the air tool will decrease to the point where the air tool will not do the job it was designed to do.

Adding another tank might resolve that.

Add another air tank

When you add another air tank, when you are not using compressed air, your air compressor will run and fill both tanks – the one that came with the compressor and the one you have just added.

This means that the air compressor motor will run longer before reaching cut out pressure and stopping. The compressor pump is now filling a larger volume.

Note that you must make sure that your air compressor will handle the increased run time. If the duty cycle of the air compressor is too low – that’s the maximum run time allowable to avoid compressor overheating – then adding a tank may make your compressor run too long at any one time, and that may damage the compressor motor.

The manuals for the lower cost DIY air compressors may not even show you what your compressor duty cycle is. If your air compressor manual does not indicate the duty cycle of your brand and model, then our rule of thumb is that your air compressor should only run for a maximum of ten consecutive minutes. If it needs to run longer to fill the tanks, the we shut it down and let it cool for fifteen minutes before running the compressor again. After the compressor motor has cooled down, we will run the compressor again for the maximum ten minutes or until both tanks are full to the cut out pressure setting and the compressor stops automatically, whichever comes first.

Having the extra tank, means that you now will have a  much larger reservoir of pre-compressed air to use when you next run your higher demand air tool.Just watch out for compressor overheating.

Plumbing your new air tank

You can use one similar to the “air pig” shown in the image.

Portable compressed air tankPlumbing would need to be modified so that air from the compressor pump would flow both into the main tank on the compressor and this new tank at the same time.

Plumbed this way the one pressure switch on the air compressor would monitor the pressure in both tanks and shut the air compressor off when the pressure reached in both tanks reached the normal cut out setting of the original compressor and tank.

To add a tank to your DIY type air compressor, the simplest way is to add a tee to the tank. See the sketch below.

How to add an air tank

  1. The first air line is plugged into the discharge coupler on the compressor
  2. The other end of that air line has a coupler
  3. Plug that air line coupler onto the connector on the secondary tank
  4. Since the coupler on the other side of the Tee on the portable tank is checked, air will not flow out until a mating connector is inserted into the coupler on the secondary tank
  5. When you need air at the job, plug a second air line into the discharge coupler on the secondary tank, and air from both compressor tank and secondary tank will flow down the line to your air tool

Place Second Air Tank Near Job

Another benefit of having a secondary tank is that the secondary tank can be placed nearer the job site more easily.

To use an air nailer for shingles on a roof for example,  it would be so much more convenient to leave the heavy air compressor at ground level, run an air line from it up to the secondary portable tank on the roof, and then run an air line from the secondary tank to the nail gun. More convenient to move around and more air supply closer to the nail gun are significant benefits.

If you add another air tank to your air compressor, you will be able to use higher demand air tools for a longer period of time. If, however, the air supply and pressure diminishes still, and your air tool starts to wind down, then stop, take a break, and let the air tanks come back up to cut out pressure.

Just be mindful of the duty cycle.


  1. Thanasis says:

    I have a Werther TC-108 Special compressor with an 1.5liter air tank. I want to add a second tank in order to achieve higher air brushing times without the need of turning on again the compressor. Is it possible to auto switch to the second air tank when the 1.5L gets full? What kind of materials I’ll need and the second air tank how much pressure must withstand ? Thanks

    Bar 3.8/psi 55
    L/min 23/cfm 0.74

    • willyr says:

      The information on the page explains the process of adding a second tank, Thanassis. I don’t know what you mean by “auto switch”? If the discharge coupling is connected to the second tank, and you are drawing air from the second tank, as you draw air, more will flow from the compressor tank until such time as the compressor tank drops to the cut in pressure, and the compressor will start. Any tanks you use must be rated to withstand higher pressures than the maximum pressure the compressor can deliver.

      • Thanasis says:

        I want to connect and use both tanks to the same compressor. So i will use a 1/8 T connector. By saying “auto switch” I mean a valve (if there is any) to automatically stop the air from the air tank.

        • I’m trying to understand why this is important? If you have air running to both tanks from the same compressor, with a check valve in each line from the tank before it gets to the Tee, the compressor will still run the same length of time as if it were filling two separate tanks? What is the need to isolate one tank with an “automatic valve”? Yes, you can do it, provided you have power and a signal, or perhaps with air logic devices, but how come this is necessary, please?

  2. Joshua Strauss says:

    Okay so I have 2 compressors both 30-40gal. Compressor a had bad motor good tank. Compressor b has good motor and tank.

    If I take compressor b line from motor and put a tee coupler with a line going to tank a and b and the two going into shut off regulator, and then put my quick connect on compressor a, I will have doubled my capacity, correct?

    • If by capacity you mean available pre-compressed air, when both tanks are full, and the compressor is off, then yes. Of course, the motor and pump and compressor B will run twice as long to fill the two tanks.

  3. In my effort to add a tank, i want to tee off just before the check valve threaded into the tank.

    What i am finding is that while it is a compression fitting, the discharge line is NOT a true 3/8″ or 1/2″ line, and the nut is 3/8″ PIPE threads!

    So, based on the pic i included with this question, how would i still be able to use a compression fitting tee for both the discharge line AND the Auxiliary tank line AND thread the third tee opening onto the check valve inlet?

    • Is the threaded port to the left is the metal air line from the pump to the tank, and the larger threaded boss at the bottom of your photo is threaded into the tank? And you need one more line to pull air from the tank to a secondary tank? I wouldn’t install it here, it were me. I’d install a Tee at the port for the discharge coupler, removing the coupler, installing a tee there, reinstalling the coupler on one leg, and the additional air line to the new tank on the other. That line should have a one-way valve in it.

  4. I have a porter cable pancake 6 gal for jobs on site. But I want a bigger and more powerful compressor in my basement workshop that will be static.

    Somebody gave me a porter cable compressor 20gal 135psi 5.3cfm@90psi with a cracked tank. The compressor is almost brand new(he didn’t drain the tank and wasn’t using it often).

    And I have an other porter cable 6gal pancake which the compressor is busted.

    My question is is it possible to build a station in my workshop using 2 portable 10 gal tank with my 6gal pancake tank plugged on my compressor who was on the 20gal tank. That would give me 26 gal. I’d use it for nail gun and spray paint etc wich I guess would be plenty enough.

  5. raymond cowell says:

    will my compressor run less by doing this with a smaller compressor to larger tank

    • Raymond, there is no “free energy”. If you connect a small air compressor to a larger air tank than came with it, then the small air compressor will have to run longer to fill that larger tank. The larger the tank, the longer the small compressor will have to run. If the new tank is too large, that threatens the small air compressor, as it may surpass its duty cycle, and that may damage the compressor. On the other hand, if you can fill the larger tank with a small compressor, and give the small compressor lots of time to cool before it runs again, then you will have a larger reservoir of compressed air to draw from for your air tool. Whether you can fill that larger tank with your small air compressor will depend on make and model of compressor, and size of the tank.

  6. So i have an old twin tank compressor with the motor shot. I ripped the motor off and ran a line in from the compressor at the bottom and a line out at the top to the gun. The piggy back tank is in series with the compressor. That probably will not give me the desired affect will it? What i need to do is cap off the bottom and then put a tee at the top for air in and out so it can use the same pressure switch? Or should it work the way i have it set up?

    • The way to install a second tank is as it’s recommended here: // . If you have problems with that, please advise. We certainly do NOT recommend taking a feed from the bottom of a compressor tank, as you will get a great deal of water and sludge along with the compressed air.

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