Eliminating Pressure Problems in Compressed Air Systems

A couple of key principles must be considered if we want to understand and control the operating costs of your compressed air system. First, compressors pump air, they do not make pressure. The system creates the back pressure which the compressors must pump against. When the compressor delivers more air than the demand requires, the pressure rises and of course, the reverse is also true. Secondly, any component or application which forces the pressure to be higher than necessary creates wasted energy in the system. This waste is not linear to the increase in pressure but can be exponential for many reasons. However, the main contributors are artificial demand and the size of the compressors in the system. In our experience, 25-30% of the horsepower on line in most systems is due to unnecessarily high system pressure. Therefore, if we identify and correct the applications that are driving the requirement for higher system pressure, we can turn off compressors. This is not to say that there aren't problems and opportunities in the compressor room, but the production department's requirements for pressure will normally out-weigh any available compressor control refinements. The key benefit which must be communicated to production is that the application will no longer be sensitive to system pressure. It becomes more reliable and repetitive, which increases quality and productivity. Determine Where the Inefficiency Lies The simplest way to determine which applications are driving the system pressure is to ask the compressor operators which applications are the most sensitive to pressure fluctuations. The compressor operators usually receive a phone call from production personnel if a compressed air application is not performing correctly. Talking to the production personnel who call identifies the application which is not performing reliably. Unfortunately, the phone call often generates an adjustment in the compressor operating arrangement or pressure until the application performs acceptably. This is a minimum acceptable standards approach which does not look at the process to determine what may have changed. Instead, it compensates for all problems with increased system pressure. For example, if a filter clogs up or a leak occurs at the point of use on a critical application, higher pressure for the entire system will be required to provide the same pressure to the application. Therefore, the pressure required is determined by the cumulative delta pressures in the system added to the actual pressure required at the inlet to the device - called the article pressure. Diagram #1 depicts an actual system pressure profile and is typical of most systems we audit. When a profile is presented in this manner it is easier to determine where the greatest pressure losses are located and how to improve the performance of an application.