I think most of us know that 3/8th inch air hose is supposed to be better than ¼ inch when more power is required for air tools. Although most woodworking does not require air tools that need a high volume of airflow, many of us use air tools for other hobbies.
I'm in a Gas Dynamics class at school and got to thinking exactly how much better is 3/8th inch than ¼ inch and when are the effects noticeable. I determined, from calculations shown below, the theoretical max air flow for ¼ inch is 13.35 CFM and for 3/8th inch, max air flow is 30.05 CFM. These numbers represent the max air flow out of a compressor with the regulator set to 90 PSI assuming no losses to friction or other inefficiencies. (In reality for a 50' hose we could expect roughly 10% loss.)
What does this mean? First if you have a compressor with a high output you immediately restrict your max air flow to 13.35 CFM if you have any quarter inch fittings, hoses or other connections in your set up. Second, you still can benefit from a 3/8th inch hose if your compressor can't output more than 13.35 CFM. If you have a large tank, as long as your output pressure remains above 90 PSI, with a 3/8th inch hose you still can get a flow above 13.35 CFM. Though you will only be able to maintain that flow rate until your tank pressure drops below 90 PSI.
In conclusion if you don't have any tools, or anticipate buying any, that require close to or more than 13.35 CFM it is a safe bet to stick with the standard ¼ inch hose and fittings. But if you need to run bigger impact wrenches or other high flow tools, it would probably be a worthwhile investment to upgrade to 3/8th. I am not familiar with any, but if you had a tool that required a high volume of air flow only for an instant, with a 3/8th inch hose you may be able to get by using an under powered compressor if you have a large enough tank. (How long it would work is a calculation for another day.) These calculations were made assuming isentropic flow, at sea level, with an ambient temperature of 70℉. Again in reality you can assume around a 10% loss. You can calculate other flow rates using the same equation, just substitute in your hose diameter and operating pressure. PS all calculations were done in SI units then converted back to standard.
Let me know what you think or if my math or logic is wrong.
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I'm in a Gas Dynamics class at school and got to thinking exactly how much better is 3/8th inch than ¼ inch and when are the effects noticeable. I determined, from calculations shown below, the theoretical max air flow for ¼ inch is 13.35 CFM and for 3/8th inch, max air flow is 30.05 CFM. These numbers represent the max air flow out of a compressor with the regulator set to 90 PSI assuming no losses to friction or other inefficiencies. (In reality for a 50' hose we could expect roughly 10% loss.)
What does this mean? First if you have a compressor with a high output you immediately restrict your max air flow to 13.35 CFM if you have any quarter inch fittings, hoses or other connections in your set up. Second, you still can benefit from a 3/8th inch hose if your compressor can't output more than 13.35 CFM. If you have a large tank, as long as your output pressure remains above 90 PSI, with a 3/8th inch hose you still can get a flow above 13.35 CFM. Though you will only be able to maintain that flow rate until your tank pressure drops below 90 PSI.
In conclusion if you don't have any tools, or anticipate buying any, that require close to or more than 13.35 CFM it is a safe bet to stick with the standard ¼ inch hose and fittings. But if you need to run bigger impact wrenches or other high flow tools, it would probably be a worthwhile investment to upgrade to 3/8th. I am not familiar with any, but if you had a tool that required a high volume of air flow only for an instant, with a 3/8th inch hose you may be able to get by using an under powered compressor if you have a large enough tank. (How long it would work is a calculation for another day.) These calculations were made assuming isentropic flow, at sea level, with an ambient temperature of 70℉. Again in reality you can assume around a 10% loss. You can calculate other flow rates using the same equation, just substitute in your hose diameter and operating pressure. PS all calculations were done in SI units then converted back to standard.
Let me know what you think or if my math or logic is wrong.
