When connecting and piping in air compressors, it pays to be careful with piping arrangement to ensure there are no areas of restriction. The pictured piping element is just one example. The installer did a good job in installing a 45° angle entry to the header, which is a great idea for any entry into the piping header. However, the designer did not consider the large amount of air passing through this connection, resulting in a restriction.
The discharge piping size of the compressors is 4 in., quite small for the 4,000-cfm capacity of the compressor. This size is typically supplied because it reduces the cost to build the compressor; the compressor manufacturers assume that the use will properly size compressor room header piping.
Wise system designers recognize this sometimes happens and will upsize system header piping accordingly. But as it is, the design in this system called for a 6-in. Y, but since parts weren’t available, a 4-in. Y was used instead. The result is an 8-psi pressure loss right at this connection. This pressure backed up into the compressors and caused reduced flow, never allowing both compressors to achieve full load and any one time, even though the facility was experiencing low pressure.
It is best to ensure that the velocity of the compressed air at peak flows stays between 20 and 30 feet per second at pressure. In this case optimal design would call for 8- or 10-in. piping for the header.
Don’t have a compressor that size? The same principle applies for smaller systems including yours. Want to calculate pipeline velocity? Check out the calculator in the USDOE MEASUR tool available here: https://www.energy.gov/eere/amo/measur
