Answer to sTEm–at-Work Puzzle #49: Valve Selection Documentation

This puzzle continues to push students to read data presentations that have multiple plots. The graphic has three
common data response shapes and each has its own mathematical model (formula, equation).  The puzzle story emphasizes the slope concept. 

The performance of  Value PF-137 follows the classic “y= mx + b” linear model. The presence (absence) of a constant slope value is the point to emphasize with students.  As the valve is opened a "linear" response to flow will occur.  By contrast, the performance of  Valve PF-121 is not linear.  If appropriate, the equation for this curve can be discussed with your class. However, it is visually clear that initially opening the valve a lot (40% for example) does not allow 40% of full fluid flow through the valve to occur.  Since the technician wants to have a low flow of acid initially be mixed with the water in the tank, Valve PF-121 only allows about 10% of full flow when the valve is 40% open. Thus, from valve selection shown below, the tech would pick Valve PF-121.
Question: The Tech installed Valve PF-137. Yes or NO

Answer: NO