Are you constantly waiting for your air tank to refill during heavy-duty projects? Or perhaps you’re worried about downtime if your primary compressor fails during a critical job? You are not alone. Many professional mechanics and woodworkers face the limitation of single-unit airflow (CFM). The solution lies in learning how to plumb 2 air compressors to run together.
By connecting two units in parallel, you effectively double your available airflow and create a redundant system that keeps your shop running even if one unit needs maintenance. This guide will walk you through the exact plumbing diagram, necessary components, and safety checks to ensure your system runs efficiently and safely. Let’s turn your compressed air setup into a powerhouse.
Why Plumb Two Air Compressors Together?
Before we dive into the nuts and bolts (or rather, pipes and fittings), it is essential to understand why this setup is beneficial. Understanding the mechanics helps you troubleshoot later.
1. Increased CFM (Cubic Feet Per Minute)
The most common reason for a dual setup is airflow. If you use high-demand tools like sandblasters, large impact wrenches, or HVLP spray guns, a single compressor often struggles. By plumbing two compressors together, you add their CFM ratings. For example, two 5 CFM compressors become a 10 CFM system.
2. System Redundancy
In a professional shop, time is money. If your only compressor burns out, work stops. With a parallel setup, if one unit fails, the other can often keep essential tools running while you repair the first.
3. Extended Motor Life
When demand is high, a single compressor runs continuously, leading to heat buildup and wear. Two compressors sharing the load can cycle on and off more reasonably, potentially extending the lifespan of both motors.
Expert Note: According to fluid dynamics principles, connecting tanks in parallel increases volume but requires careful pressure management to ensure both tanks equalize correctly. For more on the physics of gas compression, you can refer to the fundamental concepts on Wikipedia’s Compressed Air page.
Essential Components for Your Dual Setup
You cannot simply hose two compressors together. You need specific components to manage pressure, prevent backflow, and ensure safety. Here is your shopping list:
Check Valves (One-Way Valves):Crucial. These prevent air from one compressor from flowing back into the other when it is not running. Without these, you risk damaging the pump heads.
Union Tees or Manifold Block: To join the output lines cleanly.
Ball Valves: Install these on each compressor’s output line. This allows you to isolate one unit for maintenance without shutting down the entire system.
Pressure Switch (Master/Slave Configuration): Ideally, you want one compressor to kick on at a slightly lower pressure than the other, or use a dedicated dual-compressor controller.
High-Quality Air Hose: Use nylon or polyurethane tubing rated for at least 150 PSI.
Teflon Tape & Pipe Dope: For leak-proof threaded connections.
Step-by-Step Diagram: How to Plumb 2 Air Compressors
While every shop layout is different, the core logic remains the same. We will use a “Common Header” approach, which is the industry standard for reliability.
Step 1: Positioning the Units
Place your two compressors near each other but ensure there is at least 6–12 inches of space between them for ventilation. Heat is the enemy of compressors; poor airflow leads to premature failure.
Step 2: Installing Check Valves
Locate the discharge port (output) on each compressor.
Apply Teflon tape to the threads of the discharge port.
Screw in a Check Valve. Ensure the arrow on the valve points away from the compressor and toward your main air line.
Tighten securely, but do not overtighten plastic fittings.
Step 3: Adding Isolation Ball Valves
Immediately after the check valve, install a Ball Valve.
Why? This allows you to shut off air from Compressor A while Compressor B is still running. This is vital for changing oil, filters, or repairs.
Step 4: Creating the Common Header
Now, you need to join the lines from both compressors.
Use a Union Tee fitting.
Connect the output of Compressor A to one side of the Tee.
Connect the output of Compressor B to the other side of the Tee.
The bottom (or center) of the Tee becomes your Main Output Line that goes to your air dryer, filter, or tool manifold.
Step 5: Pressure Switch Configuration (The “Brain”)
This is where most DIYers fail. If both compressors have identical cut-in/cut-out pressures (e.g., both turn on at 90 PSI and off at 120 PSI), they will “short cycle” or fight each other.
Compressor 1 (Primary): Set cut-in at 90 PSI, cut-out at 120 PSI.
Compressor 2 (Secondary): Set cut-in at 85 PSI, cut-out at 120 PSI.
Result: Compressor 2 starts first. If demand is high and pressure drops further, Compressor 1 kicks in. When pressure hits 120 PSI, both stop.
Option B: Dedicated Dual Controller (Professional Method) For optimal efficiency, install an external pressure switch that controls both units via relays. This ensures perfect alternation and load balancing.
Visualizing the Flow
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Critical Safety Checks Before Startup
Never skip this phase. Compressed air stores significant energy and can be dangerous if mishandled.
Leak Test: Close all ball valves. Turn on Compressor A. Listen for hissing at the connections. Use a soapy water solution on joints; bubbles indicate leaks.
Check Valve Verification: With both compressors off and tanks pressurized, close the ball valve on Compressor A. Open the drain on Compressor A. If air rushes out from Compressor B’s line, your check valve is installed backward or is faulty.
Electrical Load: Ensure your circuit breaker can handle the starting amperage of both compressors if they were to start simultaneously (though staggered settings prevent this). Most 20-gallon compressors require a dedicated 20A circuit each.
Troubleshooting Common Issues
Even with a perfect diagram, issues can arise. Here is how to fix them.
Issue
Possible Cause
Solution
One compressor never turns on
Pressure settings are too far apart.
Adjust the cut-in pressure of the secondary unit closer to the primary.
Air leaks from the idle compressor
Faulty or missing check valve.
Replace the check valve immediately.
Motors overheat
Poor ventilation or continuous duty.
Increase spacing between units; check for air leaks in tools.
Pressure fluctuates wildly
Tank size mismatch.
Try to use compressors with similar tank sizes for smoother operation.
FAQ: Frequently Asked Questions
1. Can I connect two air compressors with different tank sizes?
Yes, you can. However, the larger tank will act as a buffer, causing the smaller compressor to cycle more frequently. It is best to stagger the pressure settings so the larger unit handles the baseline load and the smaller unit kicks in during peak demand.
2. Do I need a check valve for each compressor?
Absolutely. This is non-negotiable. Without check valves, air from the pressurized tank of the running compressor will flow back into the unpowered compressor’s pump head. This can cause the motor to spin backward, damage pistons, or prevent the idle compressor from starting due to back-pressure.
3. Will plumbing two compressors together double my PSI?
No. Connecting compressors in parallel increases CFM (volume), not PSI (pressure). The maximum pressure will be determined by the highest cut-out setting of your pressure switches (usually 120–150 PSI). To increase PSI, you would need a booster pump, not a parallel setup.
4. Can I use different brands of compressors?
Yes, brand does not matter as long as the fittings are compatible (usually NPT threads in the US). However, try to match the voltage and phase (e.g., both 110V or both 220V) to simplify your electrical wiring.
5. How do I drain moisture from a dual system?
Each compressor tank has its own drain valve. You must drain both tanks regularly. Moisture does not travel freely between tanks if check valves are installed correctly. Consider installing an automatic drain timer on each unit for convenience.
6. Is it better to series or parallel plumb compressors?
For almost all workshop applications, parallel is the correct choice. Series plumbing (output of one into the input of another) is used only for specialized high-pressure applications and requires specific multi-stage compressors. Parallel plumbing increases volume (CFM), which is what most tools need.
Conclusion
Learning how to plumb 2 air compressors to run together is a game-changer for any serious DIYer or professional. By following the diagram outlined above—specifically focusing on check valves, isolation ball valves, and staggered pressure settings—you can build a robust, high-CFM air system that rivals industrial setups.
Remember, safety is paramount. Double-check your connections, test for leaks, and ensure your electrical circuits can handle the load. Once set up, you’ll enjoy uninterrupted airflow, reduced wait times, and the peace of mind that comes with system redundancy.
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