A large industrial user installed a pressure/flow controller in its system to regulate the plant pressure to a constant level. The lower plant pressure reduces the extra flow (called artificial demand) that is caused by running production machinery at a higher pressure than is needed. The lower the flow, the lower the electricity bill. Flow reduction is roughly 1% for every 1 psi in lower pressure.
The pressure/flow controller had been operating successfully at 85 psi for a long period of time. But during a period of time, some mechanical problems appeared in one of their production machines. The manufacturer was called in and proclaimed the machines needed to run at higher pressure — even though the production had operated successfully at lower pressure for months. For this reason, the pressure/flow controller pressure was jacked up by 6 psi.
Fortunately, the system was being monitored by measuring instruments. The staff went back and analyzed when the machines had the problems and found that a number of transient events had occurred that forced the plant pressure to very low levels. They could see that this occurrence had caused the production problems, not the lower average pressure due to the pressure/flow controller. They could also see that the higher pressure level did not hold over the long term. Because the plant was now demanding more flow, the average pressure was actually lower at the critical production machine than before, caused by higher than desired plant flow, but with no production complaints. The electrical operating costs during this period were also higher.
They concluded that setting the pressure/flow controller higher was a placebo effect; it made production happy because they could see the higher setting pressure on the pressure/flow controller digital display, but really caused no additional benefit to the pressure level. The lower setting was returned and compressed air production returned to normal.
This exercise shows that it is important to have system monitoring in place — the data is very useful in troubleshooting strange events!
