Add A Compressor

This question arrived recently at the Ask page of this website.

I have written about this issue a number of times, and thought I would consolidate the various writings on one page for the benefit of those wondering if they should add a compressor.

Here is the latest question:

What's the safest and most reliable way to connect two electric air compressors ( add a compressor ) in order to run an air tool that requires more air (i.e. higher SCFM output)?

I saw a previous answer that suggested that:

1. both compressors would lead into the same air main, and it might be helpful to have that main lead into another receiver before pulling air to the application

2. that in the lines from each compressor, I would install a check valve that allows outflow only. That way, if one compressor is running behind on recharge, the other one's output won't flow into the other compressor's receiver.

On another web site though I saw a suggestion that the tanks on both compressors should be directly connected. So that confused me somewhat. Perhaps that approach is more applicable to vertical compressors with very large tanks.

Anyway, if the suggested approach in the first answer is safe etc, I'd appreciate a bit more detail on what the most practical way is to connect the air hose from the two compressors into a main line, including preferred location for installing check valves.

Since I currently have quick connect couplings on the Makita, I was thinking that there's probably some kind of T-fitting or manifold that one could jerry rig.

Thanks.

Response

Combining two compressors becomes a bit more complex than simply adding another air tank because the second compressor, too, has a pressure switch and possibly different cut-in and cut-out pressure settings.

If you simply were adding a tank, then the two (or three, or four) tanks would enlarge the reservoir of the one compressor, meaning it would run longer to fill the larger reservoir, but then you would have more pre-compressed air to draw on when running an application.

Duty Cycle

When you add a tank, the primary concern is the existing compressor's duty cycle.

The reason folks want to add another compressor instead of just another air tank to their air supply is to augment the compressed air flow.

One smaller compressor, though it can deliver the pressure needed for the air tool or air fixture, is not be big enough to ensure a continuous flow of compressed air at that required pressure to keep the application running satisfactorily.

So, we either upsize the existing compressor to a larger and more expensive model, or we decide to add another compressor to the circuit, to solve the flow problem.

Rule Of Thumb

The rule of thumb for compressor productivity is that each horsepower of electric motor size can deliver about 3-4 CFM of compressed air at 90 PSI.

If you are running a 10 HP compressor, it will theoretically generate around 40 CFM of compressed air at 90 PSI.

If your air tool requires 80 CFM of compressed air at 90 PSI, then you won't be able to run that air tool very long before the compressor tank(s) are emptied, and the compressor is unable to supply enough air.