I've found that those cheap compressors like the one you're using as an example from Amazon, don't really spec the CFM at the outlet, but the SCFM at the breather. It's really confusing, because they're indicating the air consumption of the compressor when outputting air at some pressure (normally 90 PSIG)...
Thanks for the comment Oscar. Yup, some industrial compressors rated in SCFM too. The one selected as an example in my lecture uses 4 CFM @ 90 psig, but you are correct about the hobby compressors. Some are rated in SCFM where it is understood that the inlet pressure is 14.7 psia or 0 psig. My understanding is the rating of compressor is the maximum operating parameter. Although some are rated in CFM, most compressors have a CFM at a set pressure. You can tell it’s a higher quality compressor if it has two ratings in CFM at different pressures. All flowrate ratings are valid maximum operating parameters. It’s just a matter of doing the math to see what the flow is at whatever your operating pressure is. Having two ratings, typically one higher and one lower value gives you a ballpark range that allows you to select a compressor without doing all the math which I discussed in this lecture. It’s funny how the cheaper ones give a rating in SCFM which requires a detailed understanding of the math to figure out if it works for you, and the higher quality ones, typically used by those who can do that math, are rated in a way where the math isn’t really required. 🙂
Hello Sir, that was so helpful. i am just confused about SCFM. you mentioned SCFM as inlet volume of air which i read in other articles that SCFM is cfm at standard condition 14.7 psia and about 70 farenhite. van you please explain .
On a complex plant we had a compressor sized at 300kW for given conditions yet later in the detailed stage the same vendor calculates 400kW what must have changed, would the ambient air temperature if changed from 49C to 42C make that kind of difference or would the system have changed?
I don't know the details of the system, but it seems as though you're also not aware if the system changed. Therefore, I cannot be said for sure if it was due to a system change without knowing more about the system itself. With that said, it could most definitely be that the system has changed and that possibly someone added some actuators or maybe the loans themselves changed or the operational parameters in some manner of the pneumatic system changed, such as actuator speed. All of those are possible and can explain why thew compressor would have consumer more power. You mentioned that the temperature changed from a hotter temperature to a colder temperature. In this case, if the system parameters had not changed, the compressor would consume less power. This is because it takes more energy to compress warmer air than it does to compress cooler air. Might be happy to advise you further if I could get some more details of specific changes that you may have considered change the power consumption.
I've found that those cheap compressors like the one you're using as an example from Amazon, don't really spec the CFM at the outlet, but the SCFM at the breather. It's really confusing, because they're indicating the air consumption of the compressor when outputting air at some pressure (normally 90 PSIG)...
Thanks for the comment Oscar.
Yup, some industrial compressors rated in SCFM too. The one selected as an example in my lecture uses 4 CFM @ 90 psig, but you are correct about the hobby compressors. Some are rated in SCFM where it is understood that the inlet pressure is 14.7 psia or 0 psig. My understanding is the rating of compressor is the maximum operating parameter. Although some are rated in CFM, most compressors have a CFM at a set pressure. You can tell it’s a higher quality compressor if it has two ratings in CFM at different pressures.
All flowrate ratings are valid maximum operating parameters. It’s just a matter of doing the math to see what the flow is at whatever your operating pressure is. Having two ratings, typically one higher and one lower value gives you a ballpark range that allows you to select a compressor without doing all the math which I discussed in this lecture.
It’s funny how the cheaper ones give a rating in SCFM which requires a detailed understanding of the math to figure out if it works for you, and the higher quality ones, typically used by those who can do that math, are rated in a way where the math isn’t really required. 🙂
please how to select a compressor for liquifaction of a 1000kh/h of boil of ethylen gas.
please tell how to calculate the time required to fill the tank in 1 minute
Hello Sir, that was so helpful. i am just confused about SCFM. you mentioned SCFM as inlet volume of air which i read in other articles that SCFM is cfm at standard condition 14.7 psia and about 70 farenhite.
van you please explain .
Pls tell m we, how calculat compressor select
On a complex plant we had a compressor sized at 300kW for given conditions yet later in the detailed stage the same vendor calculates 400kW what must have changed, would the ambient air temperature if changed from 49C to 42C make that kind of difference or would the system have changed?
I don't know the details of the system, but it seems as though you're also not aware if the system changed. Therefore, I cannot be said for sure if it was due to a system change without knowing more about the system itself.
With that said, it could most definitely be that the system has changed and that possibly someone added some actuators or maybe the loans themselves changed or the operational parameters in some manner of the pneumatic system changed, such as actuator speed. All of those are possible and can explain why thew compressor would have consumer more power.
You mentioned that the temperature changed from a hotter temperature to a colder temperature. In this case, if the system parameters had not changed, the compressor would consume less power. This is because it takes more energy to compress warmer air than it does to compress cooler air.
Might be happy to advise you further if I could get some more details of specific changes that you may have considered change the power consumption.