advantage to turning down a 2 stage air compressor?

[metalmagpie]

I've been monkeying with compressors this year, and am almost done putting one together. It is a 2 stage 4 cylinder Champion. I read somewhere that if I change the range on my pressure switch from e.g. 120-175 to 90-120 that I can actually get more cfm out of it. I don't really need the higher pressure for anything. My biggest demand applications are a blasting cabinet and a needle gun.

Trying to think the question through analytically breaks my brain. There has been enough BS written about air compressors that I don't really trust anyone's white paper. What is the actual truth - can I get more cfm out of my compressor if I run it at lower pressure? After all, if you look at air pump ratings they say things like 11 cfm @ 90psi or 8 cfm @ 120 psi - it does seem as though running it at higher pressure results in lower CFM.

metalmagpie

 

[isb cornbinder]

Go on-line and find the manufacturer's page. Look for the specifications. If you have some trouble, call the customer help line. I never ask for help on a forum. The risks are high that there will be many conflicting answers.
If your compressor is not worn out the CFM should always be close to the same out-put. It is possible for the RPM of the compressor to reduce as it is loaded. It takes more energy to push 175 psi than 125psi. When the pressure in the tank is higher the compressor must work harder to move air into the tank.
Try to match your compressor to the available power supply. This could be your limiting factor.
I have an INGERSOL T30. I have noticed the compressor slow a little as the pressure builds up. No worry.

 

[larry_g]

Flow volumn times pressure equals the energy delivered. What your specs are saying is that if you measure your flow at a given pressure that the pump will deliver that flow at that pressure. Ifyou relly are conserned about CFM's then buy a window fan. They have a lot of flow but no pressure to speak of. For blasting you want power not necessarly flow and power is a product of pressure and flow.

lg
no neat sig line

 

[05snopro440]

I could buy that higher pressure would give you higher flow except that the air line and tool is the restriction of the flow.

My 55-gallon compressor has a 90-120 switch and it runs my sandblast cabinet, air sander, air impact, etc. just fine. In my case I'm sometimes regulating my pressure down for my tools anyways, so I don't see the advantage to running higher pressure in the tank.

You'll also use more power if you're compressing the air to a higher pressure than you actually need.

If 90-120 is sufficient for what you're running that sounds like the better option to me.

 

[TRWham]

Remember that compressor flow is measured on the suction side at atmospheric pressure. A reciprocating compressor will produce more net intake volume at lower discharge pressure because of the re-expansion of compressed air trapped in the clearance volume of the cylinder (all of the space between the piston and bore and in the valves and ports). Some of the piston stroke is spent re-expanding that air rather than drawing new air into the cylinder to be compressed, and the higher the discharge pressure, the more that trapped air must be expanded before the pump can draw in more air.

That is all assuming you are pumping everything up to your cut-out pressure all the time. When you are actually using a compressor and it is running below the cut-out pressure as it tries to keep up with demand, then it is running at the current tank pressure regardless of your pressure switch setting, so you cannot really gain more capacity by setting the cut-out lower.

 

[metalmagpie]

I can see this is fairly new ground for some of you all. I suggest you have a look at this:

https://fluidairedynamics.com/blogs/articles/how-can-i-get-more-cfm-from-my-air-compressor

It talks about ways to get more usable CFM out of your system, and their #1 trick is to turn down the pressure.

metalmagpie

 

[finn]

I can see this is fairly new ground for some of you all. I suggest you have a look at this:

https://fluidairedynamics.com/blogs/articles/how-can-i-get-more-cfm-from-my-air-compressor

It talks about ways to get more usable CFM out of your system, and their #1 trick is to turn down the pressure.

metalmagpie

I think they’re just saying to regulate your air pressure to whatever is actually required to run your tools, which is why you have a regulator in the first place. If your blast cabinet /gun is rated at 90 psi, set your regulator to 90 psi, not 175 psi.

Dialing your compressor down means you don’t store as much air reserve in your tank, so the compressor will turn on sooner.

 

[larry_g]

Your article talks about industrial air systems. What it says to me is that IF you can run the plant at a lower pressure then do so and it will save you money. But the last section says

But what if you want to get more CFM out of your existing air compressor without lowering plant PSI? Is it possible? Well, yes…but not without making significant modifications to the system. You can’t just change some settings to increase CFM beyond the maximum the system is rated for. Getting additional CFM out of your compressor will require upgrading the compressor pump and motor - that is, adding more horsepower to the compressor. This is a major expense for a large industrial air compressor: essentially, you’re rebuilding the compressor to turn it into one with a higher CFM rating.

So if you want more power then your going to have to go to a bigger compressor.

lg
no neat sig line