A couple of months ago I received a call from a PIPE-FLO® customer in Texas. She was a plant engineer in a process plant, and the plant had a spray system where the control valve was experiencing serious cavitation issues since its installment eight years ago. The problems required maintenance every six to nine months, which was scheduled during planned outages.
She had recently attended one of our FLO-Master Training Courses, and she was looking forward to applying PIPE-FLO® to solve a real world problem.
Figure 1. Plant piping system spray header diagram.
The issues with the control valve started shortly after its installation, and the cavitation problems started after the initial system start-up. The plant system was supplying water at 120° F to a spray header. A control valve regulated the flow rate to 600 gpm. After investigating the piping system in operation, it was discovered the control valve was approximately 50% open and was continually cavitating. Based on the control valve’s position and how it was cavitating, management decided to investigate the cause of the cavitation and what could be done to improve the system’s operation.
While the plant maintenance manager was in the process of getting bids to replace the existing spray control valve with one better suited for the application, a review of the plant’s design was underway. After the review of the design documents, plant maintenance discovered the system was originally sized for a process flow rate of 800 gpm to meet future design loads. During the previous eight years of operation, the system operated at a flow rate of 600 gpm to meet the market conditions. There were no current plans to increase the flow rate to the original 800 gpm.
Figure 2. Supplied pump curve of the plant’s current feed pump.
The pump test speed according to the curve is 1750 rpm, but notice the Best Efficiency Point (BEP) flow corresponds to 1,450 gpm. The control valve manufacturer provided the performance data and Cv values for the spray control valve, and the operating data.