Your question is essentially about the best way of combining air compressors to increase flow. That subject merits its own page. If you are considering combining air compressors to increase compressed air flow to your tools, you will want to read this page.
Here is the gist of your question which I have edited only slightly to make it easier to follow:
“I have a 1.8hp 26 gallon cheap compressor with low cfm 4 @90psi; 6@40psi. I’m looking to purchase another 1.8hp with same specs operating on separate 15-20 amp breakers. My thought on joining them is by a (T) fitting and using HVLP 1/4 fittings and 3/8 hose from the compressors forward expecting pressure drop of roughly 12 psi from each compressor.
Can I run one at 102 psi (90) for 4 CFM and the other at 52 psi (40) for 6 cfm to= 10cfm? Or should they both run at same psi for a slightly lower CFM? I’m only looking to increase CFM and maintain 90 working psi for most of my tools.
I do understand that the tanks are smaller and will deplete faster, so I may add a separate air tank without a motor just for extra air. I’m trying to avoid buying a larger system to have to add 240 breaker etc and save some cash in the short term.
My goal is to run a 10 CFM sand blast cabinet to its working potential. Sorry for the long post, trying to be detailed in my question and give an accurate description of my goal. Thanks for any future help.”
Combining Air Compressors To Increase Flow
A lot of good points and issues raised in your question. Thanks for that. Let’s see if I can clarify combining air compressors to increase flow for you.
When an air compressor reaches cut out pressure and stops, the tank has a certain volume of air trapped in it at the cut out pressure. Let’s use 150 PSI as an example.
150 PSI on the regulator
If your air tool is using air at 150 PSI, that tank pressure will drop very quickly to the compressor cut in pressure setting, and the compressor will start. If the air consumption is greater than the compressor can generate, the 150 PSI will degrade rapidly, essentially to 0 PSI, as the compressor hasn’t the capacity to pump air into the tank as fast as it’s coming out.
The other issue affecting the pressure to the air tool is the amount of air, or the CFM that the air tool needs to run. The higher the demand of that air tool, the harder it will be for the compressor to keep up with the pressure and demand of the air tool. If the air compressor is too small, demand will exceed supply, and the air pressure will drop.
90 PSI on the regulator
If we dial the regulator setting down to 90 PSI from the original 150 PSI, the air compressor can still only generate the same amount of air going into the tank, yet since we are now using it at a lower pressure, and we have a reservoir of higher pressure air in the tank, it will take longer for the tank pressure to drop, the compressor will have more time to try to keep the air pressure in the tank up, and we perceive that our compressor can deliver more air at the lower pressure than at the high.
Nope. The compressor pump is a fixed output device, and when it is running, it is delivering the same amount of air into the tank all the time, regardless of the regulator setting.
We can only control flow and the pressure at use
In order to extend the pre-compressed air supply in the tank, and to try to allow the compressor more time to keep up the tank pressure, we can dial the regulator setting down to the lowest pressure at which the air tool works. This maximizes the life of the air in the compressor tank while, at the same time, throttling the speed with which the air exits the compressor tank.
If the air tool works satisfactorily then, dial the pressure down further, to the point where the air tool operates at the lowest possible pressure.
This will maximize the life of the air in the compressor tank, and allow more time for the compressor to keep filling as air is used.
Yet, if the air tool – even with the supply pressure dialed down as far as it can go – still demands more CFM at that lower pressure than the compressor pump can deliver, the pressure to the air tool will continue to drop until there is not sufficient air to run the tool properly.
At this point you have a few options.
Adding another air tank
Adding another air tank will increase the amount of air that is pre-compressed, once the air compressor has reached cut put pressure and stops.
The downside of this is that the compressor will have to work longer to fill the multiple tanks. That may create issues with the compressor motor and pump overheating, leading to breakdown or sooner, rather than later, maintenance issues.
Also, once air is being consumed by the air tool again, regardless of how many tanks of air are at full pressure, unless the total volume of all of those tanks has more air than the air tool will use during the work sessions, once again, demand for air by the air tool will outstrip the capacity of the single compressor pump to deliver air, and the air pressure will drop to the point where the air tool will not work.
Combining Air Compressors To Increase Flow – Page Two. if you have just landed on this page, we are talking about getting more air flow to an air tool. If you care to review this article from the beginning, page one of Combining Air Compressors To Increase Flow is here.
If the ability of the compressor pump on a compressor is insufficient to keep up the air flow necessary for the air tool, and as discussed, adding another air tank will not solve the problem, another solution is combining air compressor to increase flow.
Add up the compressor CFM
The two compressors referred to by the original questioner can deliver 4 CFM at 90 PSI each. By combining the two compressors, the two could deliver a flow of 8 CFM at 90 PSI.
The real question is, is 8 CFM at 90 PSI sufficient flow for the application? The original poster says “My goal is to run a 10 CFM sand blast cabinet to its working potential.”
Sorry then, the answer is no. Combining the two 1.8 HP compressors can give a combined output of 8 CFM at 90 PSI, and if the sand blast cabinet needs 10 CFM at 90 PSI, these two air compressors, even if combined, will not provide enough air.
Compressor output is often theoretical?
Another issue that would concern me about combining these two compressors to try to get a higher flow is that the output from each, the 4 CFM at 90 PSI, is – at best – theoretical.
We are all familiar with the mileage estimates for our cars. If the car manufacturer tells us we’ll get 35 miles to the gallon on such and such a model, we’ll often nod sagely, and say to ourselves, “that means 25 MPG” in the real world.
It is the same for air compressors. What they claim you will get as output flow may be inflated, or theoretical only,l and may not actually be reproducible in the real world.
Expect to get less output than advertised to reduce making a bad decision about the right air compressor for the job.
240 Volt compressor supply?
The goal of the original poster is to get two compressors that, together, will give sufficient flow at 90 PSI for the 8 CFM required by the air tool. That is doable, but not with 1.8 HP compressors.
The rule of thumb is that a user should be able to get 2-4 CFM of air at 90 PSI for each HP of electric motor size.
Since the electric motor is converting electrical supply into compressed air, 120 Volts can only provide so much power to a compressor motor. If the pump is larger than a certain size, and in my books that’s about 2.5 HP, having 120 volts as the power supply to the compressor motor limits the output.
To get lots of air for the air tools, you need a bigger compressor pump. That means a bigger compressor motor to run that bigger pump. That means you need more available power to be converted into compressed air, and that means 240 Volts is the power supply of choice for a compressor to supply high demand air tools, not 120 VAC.
But I just need 8 CFM!
That being the case, sure, you can combine two air compressors to increase the flow. You just have to make sure that the two, combined, has the real flow necessary for the air tool. Here’s how to put two air compressors together.