Sorry, I didn't "show my work" as I didn't know how much background you have on the topic. In short, we want to know how much air your compressor holds at full pressure (150psi), and how much it holds at the pressure you have the regulator set at to run your air hammer (100? 110?) so we can subtract the difference and figure out how much air you will consume before the tank pressure drops below the regulated pressure. To get your total air storage at 150 PSI:
- Determine the volume of your tank in cubic feet: You have a 30 gallon tank. Assuming those are US liquid gallons, there are 7.48052 gallons in 1 cubic foot. So we divide 30 by 7.48052 to get 4.01 rounded to 4.
- Use Boyle's Law to determine the amount of air you can store in those 4 cubic feet at an given pressure: Boyle's law states that a gas's pressure (that is, the pressure it exerts on it's container) is inversely proportional to the volume assuming the actual amount of gas (molecules) and the temperature remain constant. You are going to experience some temperature change, but not enough to really impact the outcome. Using some algebra/substitutions and some overall simplification, we arrive at a very useful formula for comparing the pressure/volume variables in two different scenarios which can be expressed as P1V1=P2V2. In other words, as long as everything else is held constant, the product of a given pressure and volume in a system remains the same as any other combination of pressure and volume.
Our goal is to determine the volume of atmospheric pressure air (pulled in through the compressor's inlet) that will be squeezed into your compressor tank once your tank pressure reads 150 PSI. We know 3 out of the 4 variables we need, and we can solve for the 4th. we have:
- P1 (atmospheric pressure) which we will assume is 14.7 PSI at sea level. If you live in the mountains, this will be slightly different.
-V1 (volume of atmospheric pressure air) - this is what we're trying to calculate.
-P2 (final pressure) is 150 PSI
-V2 (final volume) is the 4 cubic feet we calculated previously for your compressor's tank.
So P1(14.7) x V1(X) = P2(150) x V2(4) or 600/14.7 which equals 40.82. Now that you know how it works, you can use the calculator I mentioned before to get the same results by just plugging in your variables.
So no you know you are compressing 40.82 cubic feet of atmospheric air into your tank at 150 PSI. If you do this exact same thing over again but instead use the lower pressure at which you want to set your regulator for P2, you will get a lower volume. For example, using 110PSI, you will get 29.93 cubic feet. The difference between these two numbers (40.82 - 29.93 = 10.89) is the volume of air in cubic feet that is flowing out of the tank, through the hose and through your tool from the time you squeeze the trigger until the tank pressure reaches the regulated pressure. If you know your rate of consumption (estimated CFM of the tool), you can calculate the time it will take to flow that much air. If your tool happened to consume air at a rate of exactly 10.89 CFM, it would take exactly 1 minute. If your tool consumes air at double that rate (21.78 CFM), it would take half the time (30 seconds) and so on. To make this math easier, you can use the CFM and Pump Up calculator (specifically, the pump up calculator) on the Airgastech website. Note that if you plug in the correct numbers, you will get a "negative" time since you are actually "pumping down" rather than up.
