Air Compressor Auxiliary Tank Setup – Increase Your Cfm Capacity
An auxiliary tank increases the total volume of compressed air available, allowing tools to run longer before the motor kicks in and providing a buffer for high-demand tasks. To set it up, connect the primary compressor to the secondary tank using a high-flow hose and ensure both tanks have dedicated moisture drains and safety relief valves.
This configuration effectively doubles or triples your air storage, reducing “cycling” wear on your motor and providing more consistent pressure for painting or sanding.
You have likely experienced the frustration of a small compressor constantly cycling on and off while you are trying to finish a project. Whether you are running a DA sander on a cabinet door or using a spray gun for a smooth finish, running out of “breath” mid-stroke is a major workflow killer.
Adding a reserve tank is the most cost-effective way to give your shop the air capacity of a much larger industrial unit without the massive price tag. Mastering your air compressor auxiliary tank setup allows you to tackle high-demand tasks that would otherwise stall a standard pancake or small portable compressor.
In this guide, we will walk through the plumbing, safety protocols, and material selections needed to expand your air capacity. We will ensure your system remains safe, efficient, and moisture-free so you can focus on the craft rather than the equipment.
Understanding the Basics of an Air Compressor Auxiliary Tank Setup
Before we start turning wrenches, it is vital to understand what an auxiliary tank actually does for your shop. Many DIYers assume that adding a tank increases the CFM (Cubic Feet per Minute) output of the pump, but that is a common misconception.
The pump determines how fast air is replenished, but the tank determines how much air you can use before the pressure drops. By expanding your storage, you create a buffer that allows you to use tools with a higher CFM requirement than your pump can technically produce in real-time.
Think of it like a water tower; the pump may only fill it slowly, but when you open the valve, you get a massive burst of volume. This is the core benefit of a proper air compressor auxiliary tank setup in a home workshop or garage environment.
The Difference Between PSI and CFM
Pressure, measured in PSI (Pounds per Square Inch), is the force of the air, while CFM is the volume of air moving through the line. Most air tools require a specific CFM to operate correctly over a sustained period.
An auxiliary tank allows you to store a larger volume of high-pressure air so that high-CFM tools, like impact wrenches or sanders, don’t deplete the system in five seconds. This keeps the pressure steady and prevents the tool from losing power during critical cuts or finishes.
Choosing the Right Secondary Tank
You can purchase dedicated “air pigs” or portable air tanks specifically designed for this purpose. Alternatively, some woodworkers use a retired compressor tank, provided it has been inspected for rust and structural integrity.
Never use an old water heater or a propane tank for compressed air storage. These vessels are not rated for the high-pressure cycles of an air system and can become deadly shrapnel if they fail under load.
Why Your Workshop Needs More Air Volume
If you are primarily using a nail gun for trim work, you probably do not need an extra tank. However, as you move into metalworking, automotive repair, or fine woodworking finishes, the demand for air grows exponentially.
A larger air volume reduces the duty cycle of your compressor motor. Most hobbyist compressors are not designed to run 100% of the time; they need “rest” periods to cool down, or they risk burning out the capacitor or seizing the piston.
By increasing the storage capacity, the motor runs for longer stretches but stays off for much longer periods. This thermal management is key to making a budget-friendly compressor last for a decade rather than a single season.
Better Moisture Management
Compressed air generates heat, and heat holds moisture. When air sits in a large auxiliary tank, it has more time to cool down, which causes the water vapor to condense and fall to the bottom of the tank.
This acts as a natural “pre-filter” for your air lines. By the time the air reaches your paint gun or plasma cutter, it is significantly drier than if it had come straight from the hot pump of a small compressor.
Consistent Pressure for Spraying
If you are spraying lacquer or enamel, a dipping pressure gauge is your worst enemy. A small tank causes the pressure to fluctuate as the motor kicks in, leading to orange peel or uneven coats.
The extra volume of an auxiliary tank provides a “cushion” that keeps the pressure at the regulator rock-steady. This professional-level consistency is why many metalworkers and painters prioritize this upgrade early in their shop build.
Essential Tools and Materials for the Job
To do this right, you need more than just a spare hose. You want to minimize flow restriction so that the air can move freely between the primary and secondary tanks without a bottleneck.
Standard 1/4-inch fittings are common, but if you are looking for maximum performance, consider stepping up to 3/8-inch or even 1/2-inch lines for the main bridge between the tanks. This ensures the auxiliary tank can “feed” the primary line as fast as the tool demands it.
- High-Flow Couplers: Use V-style or European high-flow fittings to reduce air turbulence.
- Braided Lead-in Hose: A 3-foot to 6-foot rubber or hybrid hose is better than PVC for absorbing vibration.
- Tee Fittings: Brass or stainless steel tees to split the line at the primary compressor.
- Manual Drain Valves: Upgrade the “petcock” drains to ball valves for easier moisture removal.
- Safety Relief Valve: A must-have for every tank to prevent over-pressurization.
Selecting the Right Sealants
Do not rely on cheap plastic tape for these connections. Use a high-quality PTFE thread sealant or a dedicated pipe dope rated for pneumatic systems.
Leaks in an air system are not just annoying; they cause your compressor to run while you are not even in the shop. A single pinhole leak can cost you dollars in electricity and hours of unnecessary motor wear over a month.
Step-by-Step Installation Guide
Now that you have your materials, let’s walk through the actual assembly. Completing your air compressor auxiliary tank setup involves plumbing the tanks in “parallel” so they act as one large reservoir.
- Depressurize Everything: Turn off the power and bleed all air from the primary compressor and the auxiliary tank before starting.
- Install the Tee: Remove the main discharge coupler from your compressor and install a brass tee. One side will go to your tool hose, and the other will go to the auxiliary tank.
- Connect the Bridge Line: Run your high-flow hose from the tee to the inlet port of the secondary tank. If the secondary tank doesn’t have an inlet, use another tee at its main port.
- Add a Check Valve (Optional): Some pros install a one-way check valve so that air can flow into the auxiliary tank but won’t back-feed if the primary tank is disconnected.
- Seal and Tighten: Apply sealant to all threads and tighten with a wrench. Do not over-tighten brass fittings, as they can crack under excessive torque.
Once everything is connected, close all drain valves and flip the switch. Listen closely for the “hiss” of leaks. Use a spray bottle with soapy water to check every joint; bubbles will reveal even the smallest air escape.
Positioning the Tanks
Keep the auxiliary tank on a flat, stable surface. If it is a vertical tank, ensure it is bolted down or secured to a wall stud. Compressed air tanks are heavy, and a tip-over could shear off a brass fitting, turning the tank into a rocket.
If possible, place the auxiliary tank in a cooler part of the shop. The temperature differential helps the moisture drop out of the air more effectively, keeping your lines dry and your tools rust-free.
Safety Considerations and Pressure Management
Safety is the most critical part of any pressurized system. You are essentially building a pressure vessel, and you must treat it with respect. Every tank in the system must have its own dedicated safety relief valve (pop-off valve).
If the pressure switch on your primary compressor fails, the motor will keep pumping until something gives. Without a relief valve, the tank could rupture. Check the PSI rating on these valves to ensure they match the lower-rated tank in your system.
For example, if your compressor is rated for 150 PSI but your auxiliary tank is only rated for 125 PSI, you must set the system to stay below 125 PSI or use a regulator between them. Always build to the “weakest link” in the chain for safety.
Inspecting for Tank Corrosion
Water is the enemy of steel. Over time, moisture sitting at the bottom of a tank will cause internal pitting. This thins the metal from the inside out, making it impossible to see the danger from the exterior.
If you are using a second-hand tank, use a borescope or a bright light to inspect the interior through the drain port. If you see large flakes of rust or deep pits, discard the tank immediately. It is not worth the risk of an explosive failure.
Pressure Testing the System
After the initial air compressor auxiliary tank setup, do a “leak down” test. Fill the system to max pressure, note the gauge reading, and leave it overnight with the power off.
If the gauge drops more than a few PSI by morning, you have a leak. Finding and fixing these leaks early will save your compressor motor from short-cycling during the night and waking up the whole house.
Troubleshooting Common Issues
Even with a perfect setup, you might run into some performance hiccups. The most common complaint is that the compressor takes “too long” to fill. This is normal; you have doubled your volume, so the fill time will also double.
If the motor is struggling to start, you may have too much “head pressure” on the pump. Ensure your compressor’s unloader valve is working correctly. This valve releases the air trapped in the line between the pump and the tank so the motor can start without resistance.
Another issue is “slugs” of water reaching your tools. If this happens, your auxiliary tank is likely full of water. You must drain your tanks after every use. Installing an automatic electronic drain valve can solve this problem for busy shops.
Dealing with Pressure Drop
If your gauge says 100 PSI but your tool feels weak, you are experiencing pressure drop. This is usually caused by using 1/4-inch “skinny” hoses or restrictive quick-connects.
Switch to 3/8-inch ID (Internal Diameter) hoses for your main runs. The difference in performance for air-hungry tools like impact wrenches or grinders is night and day. Volume is just as important as pressure.
Frequently Asked Questions About Air Compressor Auxiliary Tank Setup
Can I connect two different brands of compressors together?
Yes, but it is complicated. If you connect two powered compressors, their pressure switches will fight each other. It is much easier to use one compressor as the primary pump and the second one (turned off) as a simple auxiliary storage tank.
How much extra volume do I really need?
For most DIYers, doubling your capacity is plenty. If you have a 20-gallon compressor, adding a 10 or 20-gallon auxiliary tank provides a massive boost in performance for almost any handheld air tool.
Do I need a regulator on the auxiliary tank?
You only need one regulator for the entire system, usually located at the exit point of the primary compressor. However, if your auxiliary tank has a lower PSI rating than your compressor, you must install a regulator before the air enters that tank to protect it.
Is it safe to leave the tanks pressurized?
While tanks are designed to hold pressure, it is best practice to drain them at the end of the day. This removes corrosive moisture and ensures that a failed hose won’t result in the compressor running all night in an empty shop.
Does a longer hose act as an auxiliary tank?
Technically, yes, but very poorly. A 50-foot hose holds a tiny amount of air compared to a tank. Relying on hose length actually increases pressure drop due to friction, which is the opposite of what you want.
Final Thoughts on Expanding Your Air Capacity
Building an air compressor auxiliary tank setup is one of those “wish I did this sooner” projects. It transforms a loud, struggling small-shop compressor into a capable system that can handle professional-grade tools and finishes.
By following the safety steps—inspecting your tanks, using the right fittings, and installing relief valves—you create a reliable resource for your woodworking, metalworking, and automotive projects. Remember that consistent volume is the secret to high-quality work with pneumatic tools.
Take the time to plumb your lines correctly and commit to a regular maintenance schedule of draining moisture. Your tools will run smoother, your motor will last longer, and your shop will finally have the “lungs” it needs to keep up with your creativity. Now, get out there and build something great!
