While contemplating compressed air problems over a pizza lunch, an air auditor started doing some quick calculations concerning the size of his pie and the relative cost. He found he could get a 6-in. pizza for 5 dollars but if he went with an 8-in. size, he would only have to pay 7 dollars. Using the formula for the area of a circle he found that for only 40% more cost he could get 78% more pizza … what a deal!
It struck him that similar, but more powerful, principles work for compressed air piping size relating to pressure loss. For example, looking at the pressure loss table here, we can see for a 100-hp 400 cfm compressor, the pressure loss per 1,000 feet of 2-in. piping, the most common size applied on this compressor size is 12.1 psi. But if we install a 3-in. pipe instead, we find that the pressure loss is reduced to only 1.5 psi per 1000 feet — lower by a factor of 8!
Similar relationships apply for other pipe sizes and flows, there is a huge reduction in pressure loss when going to the next size larger.
When installing compressed air piping, this should be a consideration to help reduce pressure loss. For every 2-psi reduction in discharge pressure on a 100-hp compressor there will be a one percent reduction in loaded power consumption. This would be equivalent to about one horsepower, resulting in savings worth roughly $750 per year for a compressor running full time at 10 cents per kWh.
The principle is the same no matter the piping material, black iron, steel, copper or aluminum — upsizing these pipes usually costs slightly more, but the benefits pay back year after year in reduced electrical costs due to lower pressure.
Best practices piping systems have less than 2-psi pressure drop across the full piping distribution system, not including air dryer, filter and down drop end use piping. To achieve this usually involves larger piping.
Filed Under: Pneumatic Tips