CFM and PSI

[Jspool]

 My Iron Kiss 150 lb hammer is installed and running.  I was surprised that it is running well on my 5hp 60 gal, 17cfm compressor.

Naturally, with only 60 gallons of air the compressor cycles relatively early but until pressure runs down the hammer functions quite well.

In hydraulics, psi controls power while gpm effects speed.  Does that correlate to psi and cfm?

I have a 250 gallon tank I can hook up to my compressor, or I can do that and pick up an additional 5hp compressor to double my cfm.

What would be the effect of doubling my cfm on the performance of the hammer? Will it hammer more hits per minute, or will double cfm just fill the air tanks more quickly?

[Jim Coke]

Greetings JS,

What is the recommended operating pressure of your hammer?  Adding a balist tank will not change the performance it would just increase the amount forging time at that pressure. I would not operate the hammer under the recommended pressure. 

Forge on and make beautiful things 

Jim

[swedefiddle]

Merry Almost,

The pressure regulator controls the pressure in the line/tank. The CFM is the amount of air that refills the tank(s), after it is used. Adding Tanks means it take a little longer to drain down with use, but it also takes longer to build-up. Connecting 2 Compressors means the refill time is shortened.

Increasing the regulator pressure will increase some of your Hit pressure. Just got the Hammer installed? Err on the side of caution and get used to the equipment. Keep your fingers connected to your hands. NEVER USE YOUR HAND/FINGERS TO WIPE ANYTHING ON THE DIES!!!!!!!! That is what a brush is for!!! Never use the hammer when you are tired or not focused!!

Neil

 

[Marc1]

There is a relation between the volume of your compressor tank and the flow of the pump. Increasing storage capacity is OK for a one time run but then the pump will not be able to refill in time for a second run. 

If you are running out of air at your normal working pace, you need a bigger compressor, that is a bigger pump and a bigger tank, there is no way around it. A power hammer manufacturer may underestimate the size of the compressor required for commercial reasons, but it is you that must determine how much volume of air you need. 

The CFM of your compressor has no bearing on the performance of your hammer, well, until you run out of air that is ...the pressure does, and as other have said you have to run your hammer at the pressure it is designed to take, not more nor less.  

[Jspool]

Recommended pressure is 125 to 150, but manual says you can turn it down for certain control situations. 

Neil, This is my second hammer, and I still have my digits. As a big boy, I even have a tablesaw and a buffer! Just kidding. Thanks for the reminder.

My 50 pounder doesn’t use much air, so cfm never came into question until I got this one.

[Jspool]

So,  if psi is the most predominant aspect of pneumatics, and cfm just determines how long it take for your compressor to refill, what is the significance of cylinder size (diameter) on an air hammer?  Just lower pressure requirements to achieve the same power?

[Jim Coke]

Greetings JS, 

         Just think of it as .. Pressure is the power of your hammer and the volume of air required to sustain slow or faster operation and maintain the required pressure is CFM .   

Forge on and make beautiful things 

Jim

[Marc1]

3 hours ago, Jspool said:

So,  if psi is the most predominant aspect of pneumatics, and cfm just determines how long it take for your compressor to refill, what is the significance of cylinder size (diameter) on an air hammer?  Just lower pressure requirements to achieve the same power?

if you are talking about your hammer now, think of it when not in motion for a second.

You have 60 gallons of air at 120 PSI in your tank, connected to your hammer piston that has ... say 30 square". That means that for each square inch of surface on your piston there is a downward force of 120 pounds. so 120x30= 3600 lb. That is the power of the stroke ... well sort of because when in motion you also have kinetic energy of the mass of the moving parts so substancially more, but for illustration purposes it will do. There are a series of other very interesting factors in this equation but you get the idea.

If you now have a smaller piston, say only 10 sq", the downward force of your little hammer will be 120x10= 1200 lb plus the rest that will necessarily be less because it is a lighter hammer compensated somehow by a faster stroke but still overall way less. 

You can increase the power of the thump by increasing the pressure setting on your compressor and use in that way more air but you are limited by the build of the hammer and you don't want to abuse it. Put too much pressure in it and it will be like using nitro in your car. 

[Jspool]

Got it. So if I’m operating with a 3.25” bore cylinder now at 135psi, with a 4” cylinder I only need 90 psi to accomplish the same power. (If my math is correct)

An air compressor should need to cycle less at 90psi so that would be my benefit to upgrade the cylinder to 4” (plus the ability to turn it up if I wanted to).

Thanks

[Marc1]

Yes, your maths is right, you will only need 90 psi to produce the same force when all is stationary.

However it will cycle the same not because of pressure but because of volume,  since the volume of air you will use will be larger and the pressure drops as you use air volume. If you had infinite storage, you would have some savings

Your compressor pump may stop earlier because it achieves the pressure quicker but you will be using more air per stroke due to the larger volume of your piston, so I don't see any savings there. 

You can not create energy so energy in you compressor, energy out of your hammer, mutatis mutandis, the difference shouldn't be much at all, yet when it comes to compressors, bigger is always better. 

Can you actually change the piston size like that? I thought it would be an integral part of your hammer. 

Check your hammer's specs. it should tell you the CFM/psi/rpm required. i don't know how much more compressor you need over the requirement of your hammer. The manufacturer should tell you all that. I suppose at a wild guess, 30% more would be a good thing. 

 

[swedefiddle]

Good Morning Jas,

Amount of work is like what Marc said. Surface area of a Piston is, PiR2 (cake R square, Pi R round. LOL) times Air pressure = Lbs. per square inch. Going from a 3 1/2" cylinder to a 4" cylinder so you can run lower pressure is psychological games, not rational machine math. But, you are correct, it can be done. Can, is a question of ability. Then you have to factor in Velocity. Small cylinder with higher pressure will increase velocity, over, larger cylinder with less pressure. Then there is the function of Friction. How many parts have to move, to make the Air Reaction? K.I.S.S..  I run 2 Compressors with 3 Tanks. One compressor adjusted to kick in at a slightly lower pressure. For normal air use (whatever Normal is), one Compressor cycles. When we want to draw more air, the second Compressor kicks in and maintains the working pressure. More Compressors do not mean more Power!!

I wasn't saying you were going to spank yourself in the Dies, Just sometimes with all the horsing around with machinery we forget for a "second", and then it hurts big time.

What could possibly go wrong?? Which thyme??

Neil

[Frosty]

Good explanations, well done Marc, Neil. I have just a bit to add to the PSI vs. CFM descriptions. Think of psi as horsepower and cfm  like mileage.  In Marc's example of the 30"2 piston vs the 10"2 piston the only thing I THINK he forgot to mention was the volume in the cylinder. The 30" cylinder REQUIRES 3x the CFM per stroke over the 10" cylinder. Hits 3x as hard but uses 3x the air. Yes?

Another good reason to use a larger reservoir tank is psi. As the volume is used the pressure falls, use half the air in the tank and the psi is 1/2. Multiple compressors to a large reservoir tank is a good solution. Heck if you're in a high wind area set up a wid powered compressor or two with an electric backup. Hmmm?

Frosty The Lucky.